IRG 12-40583_R_USTA_2012_wood in life.pdf

7/27/2019 IRG 12-40583_R_USTA_2012_wood in life.pdf

1/24

Proceedings IRG Annual Meeting (ISSN 2000-8953)

2012 The International Research Group on Wood Protection

IRG/WP 12-40583

THE INTERNATIONAL RESEARCH GROUP ON WOOD PROTECTION

Section 4 Processes and properties

WOOD: its importance in our life

Ilker Usta

Hacettepe University Department of Industrial Engineering

06532 Beytepe Ankara, Turkey

Paper prepared for the 43rdAnnual MeetingKuala Lumpur, Malaysia

6-10 May 2012

IRG SECRETARIAT

Box 5609

SE114 86 Stockholm

Sweden

www.irg-wp.org

Disclaimer

The opinions expressed in this document are those of the author(s) andare not necessarily the opinions or policy of the IRG Organization.


2/24

WOOD: its importance in our life

Ilker Usta

Hacettepe UniversityDepartment of Industrial Engineering 06532 Beytepe

Ankara, [email protected]

ABSTRACT

As it is described by Hoadley (1980) and Tsoumis (1991), wood is an organic material yieldedby trees which increase in diameter by the formation of new woody layers which envelop theentire stem. Wood has served man since he appeared on Earth (as a fuel and/or as a constructionmaterial for making houses, tools, weapons, furniture, packaging, paper, and artworks). It isimportant to appreciate the extent to which our civilization has evolved with a dependence uponwood due to its numerous properties and characteristic qualities. Although wood is stillcontinuing to be the main raw material for a large number of products, the other materials (suchas metals, cement, plastics, etc.) became popular in recent days regarding to the growth of theworld population and the change of the firms preferences on the production theory to carry outthe efficient competitiveness in either domestic or global market.

Nowadays, almost all the companies aim toincrease their income by the manufacturing ofthe demanded goods in the absolute fastest waywhich should be the easier and the cheaperapplication for merchandising. In this

phenomenia, wood may not be primarilyselective material even the design of indoordecorations requires the wooden construction.

However, this fiction should be essentiallychanged for our future life. Because, its aestheticappearences and its natural behaviour, wood isone of the environmentally friendly materialsand it could supply either constructional orconvertional requirements to create a greatnumber of products.

This article therefore aimed to show some explanations on why wood is important in our life.

This article is a review of literature about the natural materials with an emphasis on the structuralbehaviour, and is written as an introduction to wood for anyone who interests to the field ofconstruction. The information provided from the various books, articles and web sites have beencombined in a suitable organisation for preparation the monolithic manuscript. In order to keep

the integrity of the main text, citations were identified with a code number through the paper andthey were presented in detail on the references section.

The sections were prepared based on the following sub-headings:

WOOD: prologueWOOD: organic material comes from treesWOOD: it is a miracleWOOD: vulnerable behaviour based on the deteriorationWOOD: problems in wood constructionWOOD: treatment against biodegradationWOOD: epilogue

Keywords: wood, wood material, wood construction, vulnerable behavior of wood


3/24

WOOD: prologue

The following references were used in the preparation of this section: 1,2,3,4,5,6,7.

1 en.wikipedia.org/wiki/Tree2 Hoadly, R.B. 1980. Understanding wood (Acraftman`s guide to wood technology). The

Taunton Press, Inc., London.

3 Tsoumis, G.T. 1991. Science and technology ofwood (Structure, properties, utilisation). Van

Nostrand Reinhold, New York.

4 en.wikipedia.org/wiki/Wood5 en.wikipedia.org/wiki/Timber6 en.wikipedia.org/wiki/Lumber7 www.matbase.com/material/wood

Tree that has many secondary branches supported clear of the ground on a single main stem (ortrunk with clear apical dominance) is a resource of our life, symbol of goodness and

plentifulness, witness of history, home of many lives based on the ultra/micro-organismas. In

this context, tree is the greatest miracle of creator to human and people have used it in variousapplications for many thousands of years. Wood is one of these. [1;4]

Wood has served man since he appeared on Earth, and it has decisively contributed to hissurvival and to the development of civilization due to its numerous properties and characteristicqualities. It is important to appreciate the extent to which our civilization has evolved with adependence upon wood. Since prehistoric times, wood has been essentially used for many

purposes (primarily as a fuel and/or as a construction material for making houses, tools,weapons, furniture, packaging, paper, and artworks because of its beauty. Wood is stillcontinuing to be the main raw material for a large number of products, although othercompetitive materials (such as metals, cement, plastics, etc.) are available in recent days. After

harvesting in the forest, the wood is converted into a great number of products by sawing,slicing, gluing, chipping, pulping, modification by impregnation with chemicals or chemical

processing. Products of primary industrial processing include poles, posts, lumber, laminatedwood, veneer, plywood, particleboard, fiberboard, pulp and paper. These are made into productsfor final use such as furniture or indoor goods and various types of the wooden constructions. [2]

Wood is the hard, tough substance that forms the trunk of trees, and it has played an importantrole in the human life. Our ancestors easily discovered the wood as a useful and valuable rawmaterial due to its natural features, nuances of its structural behaviour, functions, workabilitycharacters and aesthetic property. Wood had been used for thousands of years as fuel andconstruction material for centuries, and maintain its importance even today. [7]

Wood has a long history of being used as fuel,which continues to this day, mostly in rural areasof the world. Hardwood is preferred oversoftwood because it creates less smoke and

burns longer. Adding a woodstove or fireplaceto a home is often felt to add ambiance andwarmth. Wood has been an importantconstruction material since humans began

building shelters, houses and boats. Nearly allboats were made out of wood until the late 19thcentury, and wood remain in common use todayin boat construction. [4] In buildings made ofother materials, wood will still be found as a

supporting material in either indoor or outdoorconditions, especially in roof construction, ininterior doors and their frames, and as exteriorcladding. [4]

New domestic housing in many parts of theworld today is commonly made from timber-framed construction. Engineered wood productsare becoming a bigger part of the constructionindustry. They may be used in both residentialand commercial buildings as structural andaesthetic materials. [5]


4/24

Wood used in construction includes productssuch as glued laminated timber (glulam),laminated veneer lumber (LVL), parallam and I-

joists. On the one hand these allow the use ofsmaller pieces, and on the other hand allow

bigger spans. They may also be selected forspecific projects such as public swimming poolsor ice rinks where the wood will not deterioratein the presence of certain chemicals. Theseengineered wood products prove to be moreenvironmentally friendly, and sometimescheaper, than building materials such as steel orconcrete. [5]

Wood to be used for construction work iscommonly known as lumber (usually refers to

felled trees). Lumber or timber is wood that isused in any of its stages from felling throughreadiness for use as structural material forconstruction, or wood pulp for paper production.The distinction between the two terms isdiscussed in detail elsewhere in the literature.For instance, in the United Kingdom andAustralia, "timber" is a term also used for sawnwood products (that is, boards), whereasgenerally in the United States and Canada, the

product of timber cut into boards is referred to aslumber. In this context, both terms representwood material that is supplied either rough(requiring additional cutting and shaping) orfinished (planed and cut to standardized widthand depth specified in centimeters). [5;6]

The term Timber could be explained in different aspects as follows: [5;6]Wood suitable for building or other engineering works is called timberWhen it forms a part of a living tree, it is called standing timber

When the tree has been felled, it is called rough timberWhen it has been sawn to various market forms such as beams, battens, planks etc, it is called converted timber

In the strict sense, wood is a natural composite of cellulose fibers which are strong in tension,and is embedded in a matrix of lignin which resists compression. Wood, therefore, may refer toother plant materials with comparable properties, and to constructional materials such as metal orsteel. Following properties of wood are also things to consider for its usage in construction:durability, cost, design flexibility and maintenance. [1]

Wood unsuitable for construction in its nativeform may be broken down mechanically (intofibers or chips) or chemically (into cellulose)and used as a raw material for other buildingmaterials such as chipboard, engineered wood,hardboard, medium-density fiberboard (MDF),oriented strand board (OSB). Such woodderivatives are widely used: wood fibers are animportant component of most paper, andcellulose is used as a component of some

synthetic materials. Wood derivatives can alsobe used for kinds of flooring, for examplelaminate flooring. [3]

Wood may also refer to material engineeredfrom wood (i.e. wood chips or wood fiber). Sucha material is called the composite wood; itincludes a range of derivative wood productswhich are manufactured by binding together thestrands, particles, fibers, or veneers of wood(together with adhesives to form compositematerials). Medium-density fibreboard (MDF), a

product of woods, is also used as a cheap

alternative to traditional woods. Wood is alsocommonly used as shuttering material to formthe mould into which concrete is poured duringreinforced concrete construction. [3]

Composite wood products (which are sometimescalled the engineered wood products) are madefrom the same hardwoods and softwoods used tomanufacture lumber. Composite wood productsare engineered to precise design specifications

which are tested to meet national or internationalstandards. [3]

Sawmill scraps and other wood waste can beused for engineered wood composed of wood

particles or fibers, but whole logs are usuallyused for veneers, such as plywood. Plywood isoften called the original engineered wood

product because it was one of the first to bemade by bonding together cut or refashioned

pieces of wood to form a larger and integralcomposite unit stronger and stiffer than the sum

of its parts. [3]


5/24

WOOD: organic material comes from trees

The following references were used in the preparation of this section: 3,4,7,8,9,11.

3 Tsoumis, G.T. 1991. Science and technologyof wood (Structure, properties, utilisation).Van Nostrand Reinhold, New York.

4 en.wikipedia.org/wiki/Wood7 http://www.matbase.com/material/wood/

8 www.aboutcivil.com/Properties%20of%20Wood%20and%20Timber.html

9 www.aboutcivil.com/Wood%20as%20construction%20material.html

11 www.askfactmaster.com/Wood

Wood is an organic material yielded by trees which increase in diameter by the formation

(between the existing wood and the inner bark) of new woody layers which envelop the entirestem, living branches, and roots. Technically this is known as secondary growth (or secondaryxylem in the stems of trees and other woody plants); it is the result of cell division in the vascularcambium, a lateral meristem, and subsequent expansion of the new cells. In a living tree, thesecondary xylem transfers water and nutrients to the leaves and other growing tissues, and has asupport function, enabling woody plants to reach large sizes or to stand up for themselves. [3]

The markings, called grain, found on all types ofwood, are caused by the structure of wood.Wood consists essentially of fine cellular tubes,which carry water and dissolved minerals fromthe roots to the leaves and which are arrangedmore or less vertically within the trunk. Thisusually forms straight-grained lumber. Manytypes of wood have prominent growth rings.Only a thin layer entirely surrounding the trunkgrows, this called the cambium. In most trees,the wood formed early in season is lighter ofcolour than wood growing later in the year. Newconcentric sheaths are formed around the trunkof a tree each year, the year markings. As a treegrows older the central portion of the trunk,which is called heartwood, dies completely. [7]

Wood is commonly classified as eitherhardwood or softwood. The wood from conifers(e.g. pine) is called softwood, and the woodfrom broad-leaved trees (e.g. oak) is calledhardwood. This classification is sometimesmisleading, as some hardwoods (e.g. balsa) areactually softer than most softwoods, andconversely, some softwoods (e.g. yew) areharder than most hardwoods. Additionally,woods from different types of trees havedifferent colors and grain densities. Because ofthese differences, and the fact that some woodstake longer to grow than others, wood fromdifferent kinds of trees have different qualitiesand values. For example; while mahogany is adark and dense hardwood which is excellent for

fine furniture crafting, balsa is light and soft, andalmost spongelike making it useful for modelbuilding. [11]

Physical properties of wood: The principle physical properties of wood are strength, hardness,stiffness and density. Dense types of wood are usually hard and strong. The term strength coversa number of different properties. Strength varies greatly with seasoning and with the direction ofthe grain; wood is much stronger when cut along the grain than when cut across it. Toughness isa measure of strength against sudden, repeated stress. Wood is naturally very durable. If notattacked by living things, it can last for hundreds or even for thousands of years. The most

important threat for wood are fungi that cause so-called dry rot. The heartwood of a few speciesis naturally resistant to these fungi. Other types of natural resistance to various of other types of


6/24

attack have been discovered in other species. These types are usually very aromatic. It issuspected that they are protected by the resins and other chemicals they contain. Wood may needto be preserved by protecting it chemically against deterioration. [8]

Shrinkage: Wood also shrinks as it dries, orswells as it picks up moisture, with concomitantwarpage potential. Critical in this process is thefiber saturation point, the point (about 25 %moisture content on oven-dry basis) belowwhich the hollow center of the cell has lost itsfluid contents, the cell walls begin to dry andshrink, and wood strength begins to increase.The swelling and shrinkage processes arereversible and approximately linear betweenfiber saturation point and 0 % MC. Wood decayor fungal stain do not occur when the MC is

below 20 %. There is no practical way toprevent moisture change in wood; most woodfinishes and coatings only slow the processdown. Thus, vapor barriers, adequate ventilation,exclusion of water from wood, or preservativetreatment are absolutely essential in woodconstruction. [8]

Specific gravity: Generally, specific gravity (itis synonomously used here as a density) and themajor strength properties of wood are directly

related. Specific gravity usually is usedstructural species ranges from roughly 0,30 to0,90 gcm-3. Higher allowable design values areassigned to those pieces having narrower growthrings (more rings per inch) or more denselatewood per growth ring and hence, higherspecific gravity. [8]

Moisture content: Undoubtedly, woodsreaction to moisture provides more problemsthan any other factor in its use. Wood ishygroscopic; that is, it picks up or gives offmoisture to equalize with the relative humidityand temperature in the atmosphere. As it doesso, it changes in strength; bending strength canincrease by about 50 % in going from green to amoisture content (MC) found in wood membersin a residential structure, for example. [8]

Thermal properties and temperature effects:Although wood is an excellent heat insulator, itsstrength and other properties are affectedadversely by exposure for extended periods totemperatures above about 100F (38C). Thecombination of high relative humidity or MCand high temperatures, as in unventilated atticareas, can have serious effects on roof sheathingmaterials and structural elements over and abovethe potential for attack by decay organisms.Simple remedies and caution usually preventany problems. At temperatures above 220F

(104C), wood takes on a thermoplasticbehavior. This characteristic, which is rarelyencountered in normal construction, is anadvantage in the manufacture of somereconstituted board products, where hightemperatures and pressures are utilized. [8]

Wood defects: The major problems that arise in wood use may be attributed either to the effectsof grain distortions (cell orientation or alignment), to the effects of excess moisture, or to defects

that occur as a result of the drying process. The following specific defects of wood materialtaken into account in the grading of lumber products.[9]

Knots: Knots are areas of the trunk in which thebase of a branch is embedded. When the wood issawed into planks, knots become clear assomewhat circular discontinuities orirregularities in the grain structure. The result ofcutting across a branch in lumber manufacture.If the branch is cut perpendicular to its axis, theknot is round or oblong and presents a miniatureaspect of a tree with visible growth rings. Knotsmay be live (cut through a living branch withintact tissue) or dead (cut through a dead branch

stub with loose bark, usually resulting in aknothole). If the saw is oriented so as to cutalong the length of a branch, the knot is greatlyelongated and is termed a spike knot. Knots aregenerally undesirable in lumber from thestandpoint of appearance and their negativeinfluence on the strength of the wood. Due to theobvious grain distortion around knots, they areareas of severe strength reduction. The lumbergrading process takes this into account byclassifying lumber grade by knot size, number,


7/24

type, and location within the member. Knotslocated along the edge of a piece are, forexample, restricted in size more than are knotslocated along the centerline of the member. [9]

Splits and cracks: Separations of the wood cellsalong the grain, most often the result of dryingstresses as the wood shrinks. Cracks are small,whereas splits extend completely through thethickness of a piece. Splits at the ends of themember, particularly along the central portion ofa beam, are limited in grading. [9]

Slope of grain: A deviation of cell orientationfrom the longitudinal axis of the member. Slopeof grain (of the wood) may be a natural

phenomenon wherein the grain is at some angleto the tree axis (termed spiral grain), or it may bethe result of sawing the member non-parallel tothe tree axis.Slope of grain has a negative effectupon wood strength properties. For example, aslope of 1:20 has minimal effect, but a slope of1:6 reduces strength to about 40% in bendingand to about 55% in compression parallel to the

grain. Tensile strength (of the wood material) iseven more adversely affected. [9]

Shake: A lengthwise separation of the wood,which usually occurs between or through theannual growth rings. Shakes are limited ingrading since they present a plane of greatlyreduced shear strength. Shake may occur as aresult of severe wind that bends a tree to producean internal shear failure, or as a result ofsubsequent rough handling of the tree or its

products. [9]

Wane: Lack of wood. Wane occurs whenever aboard is sawn so as to intersect the periphery of

the tree, resulting in one edge or portion of anedge of a board being rounded or including bark.Limited amounts of wane are permitted,depending upon lumber grade. The effect ofwane on wood strength or nailing surface isobvious. [9]

WOOD: it is a miracle

The following references were used in the preparation of this section: 8,10,11,12,13,14,15,16.

8 http://www.aboutcivil.com/Properties%20of%20Wood%20and%20Timber.html

10 findarticles.com/p/articles/mi_m3575/is_1281_213/ai_111268372/

11 www.askfactmaster.com/Wood

12 ezinearticles.com/?Wooden-Deck-Boards---5-Reasons-Why-Wood-is-the-Best-Material-For-Decking&id=4441832

13 www.askfactmaster.com/Five_Elements14 en.wikipedia.org/wiki/Dendrochronology15 en.wikipedia.org/wiki/Radiocarbon_dating16 http://www.essayclub.com/term-

papers/Wooden-Chopsticks/2719.html

Our existence on the planet is ecologically intimately bound to the life of trees. For instance,trees in forests have the ability to hold the large amount of carbon dioxide and through

photosynthesis they absorb carbon dioxide and release the oxygen into the atmosphere. Theeffect of forests on the atmosphere is undoubted, yet their role as the lungs of the world issometimes exaggerated. Natural forests are close to environmental equilibrium: allowing forgrowth and decay, their net wood increment is negligible, and so is their contribution to the

balance of oxygen and carbon dioxide in the atmosphere. Indeed, it is sometimes argued bymarket-orientated ecologists that grassland prairie has just about the same properties inrelationship to climate as natural forest. [10]

Global warming and greenhouse effects arecaused by human activities which includes

defrostation. Defrostation is one of the manycauses and results for climate change. In this


8/24

case, decayed or damaged trees by fires releasethose carbon that reacts with the oxygen in theair which then creates carbon dioxide.Therefore, this increases greenhouse gases andresult in speeding up global warming. Whenclimate changes rapidly, hazards such as forestfires are increased. Then this becomes cycle ofdeforestation where forest being cut and burneddown. [16]

The consequences are not only climate change,but that includes the unbalanced bio-organisms,

the decreased resources and quantity of water,the destruction of habitats for animals andinsects and erosion of soil.Trees in forests thatused to absorb carbon dioxide then release theminto to the atmosphere during the biological lifecycle, provide us with a safe environment withthe added benefits of natural beauty.Additionally, they also support to many mill andlumber cooperations, and the logging business asa main raw material. The forests in all over theworld must be saved and regulate carefully sincethey are prominent to the biodiversities andhuman beings. [16]

As it comes from tree, wood is a natural material that stores carbon and also has many practicalpurposes that enrich our lives. Wood add functionality to our lives with the benefits of carbonneutrality, beauty, warmth and security. [11]

Wood has a natural charm: There is softness and warmth found in wood that makes it uniqueto all other building materials. Not only the staining or painting the timber to express our tastesand style, but the feel and texture of wood adds to its beauty. Wood can look rugged orcontemporary and everything in between. Outdoor living is more comfortable with the charm ofwood around us. Well-designed wood structures are comfortable to live in all year round nomatter where you are. [8;12]

A particular feature of timber is the flexibility ofdesign forms and finishes that can be used. Thisflexibility also extends to the ease with which

existing buildings can be added to or modified tosuit changing circumstances. User friendlyversatile timber gives building designers creativefreedom providing homeowners with flexibledesign choices. [8;12]

Timber is simply the best building material forbuilders, designers and homeowners and can beused to construct the homes we love, structures

we admire and warehouses, commercialbuildings and other structures. The timber framemethod of building gives designers flexibility in

both layout and external appearance. High levelsof thermal insulation are incorporated within theconstruction, reducing heating costs andconserving energy. [8;12]

Wood is easy to work with: This means that wooden objects can be designed and built with ourlifestyle and tastes in mind. Because of its flexibility, professional contractors can create the

perfect outdoor living room for us using wood material. Wood is generally lightweight and easy

to cut, shape and adapt to suit our project's needs. Treated wood comes in a wide variety of pre-cut sizes and can be pieced together to build a unique structure that looks fabulous. [8;12]

Increasingly specialist timber frame and trussmanufacturers use high tech prefabricationenabling accurate and speedy installation.Recyclable timber is a forgiving material thatcan be easily disassembled and reworked. Ifdemolition or deconstruction of a wooden

building is necessary, many wood-basedproducts can be recycled or reused. [8;12]

Timber trusses and frames, factory fabricatedfrom sawn timber and toothed metal plateconnectors, have come to dominate roofconstruction for small buildings such as housesand large industrial buildings where clear spansup to 50 metres are required. Timber trussescompete with other roof structural systems oncost, high performance, versatility and readyavailability, supported by design software

packages supplied by the plate manufacturers tothe fabricators. [8;12]


9/24

Wood is strong and lightweight: Wood is strong, light and reliable making timber constructionsimpler and safer than steel or concrete construction. A comparison with steel and concreteshows that radiata pine structural timber, for example, has a strength for weight ratio 20 percenthigher than structural steel and four to five times better than unreinforced concrete incompression. People have been building with wood for thousands of years. When properly

constructed, a wood structure will last for generations and continue to look beautiful. Withtreated wood material, durability and strength are enhanced and weather and insects won't harmit. Framing and railings built with wood are strong and dependable as well, with differentdimensions and style options available. The lightweight structures possible in wood confer flow-on advantages in terms of reduced foundation costs, reduced earthquake loading and easiertransport. Building components and complete constructions are simple and safe to erect, andcheaper to deconstruct or reuse at the end of a buildings useful life. [8;12].

Wood is safe: Wood has low toxicity and therefore requires no special safety precautions towork with it, other than normal protection from dusts and splinters. Wood frame constructionrequires little in the way of heavy lifting equipment making building sites safer work places.

Wood being non-conductive has obvious benefits in terms of electrical safety. It is important toexpress that modern timber construction has increased fire resistance due to incombustiblelinings protecting light frames.Though, would is chemically inert as compared to other materials

but is affected by some acids and bases. Some species have proven very useful for foodcontainers (berry boxes and crates) because they are nontoxic and impart no taste to the foodscontained therein. Wood structures have also found widespread use as storage facilities for saltand fertilizer chemicals. [8;12]

Wood is durable: Good detailing, coating and maintenance ensure that timber structures last forlifetimes. Although many buildings become obsolete and are demolished long before the end oftheir natural lives, timber buildings correctly designed and maintained can have an indefinite life.The key to long life is protection from weather, insect attack and decay, through well-establisheddesign detailing, surface coating systems, selection of durable species, and preservativetreatment processes. In all countries of the world, and Australia is no exception, historic timber

buildings testify to these principles. [8;12]

In termite-prone areas, all buildings arevulnerable to termite attack of contents, so

protection is needed regardless of constructionmaterials. Protection systems rely on physical orchemical barriers, or both, and theireffectiveness depends on the quality of the

design, construction, inspection andmaintenance. The risk of termite attack should

be assessed after consulting with local buildingauthorities and an appropriate termitemanagement system should be implemented.[8;12]

The system may include physical or chemicalbarriers or in higher risk areas, a termite resistanttreated timber or naturally termite resistantframe may also be chosen. In any case anymanagement system should include regularinspection to ensure that barriers have not been

breached. It is therefore critical that the systemtype and inspection schedule are understood byall future householders. Importantly, termites arean integral part of the ecology of Australia,however, with awareness, planning and usingcost effective systems, they can be effectivelymanaged. [8;12]

Wood is cost effective: Wood is an economical choice. Price is often a tipping point in homerenovations. The good news is that wood material is economical when compared to otherexterior grade building materials. Not only is the product cost effective, but installation charge

tending to be lower based on the handling and flexibility of wood. Wood is also readily availablein a wide variety of sizes and dimensions, making it easy to build a custom project with in stock


10/24

materials. Comparative studies of the economics of different wall framing systems indicate that,in terms of direct building expenses, timber frames are consistently the most cost-effectivesolution. There are many factors to consider when comparing the economics of differentconstruction systems including the complexity of the layout, site, builder experience, and relativematerial prices at the time of building. However, comparative studies of the economics of

different wall framing systems indicate that, in terms of direct building expenses, timber framesare consistently the most cost-effective solution. In the medium to long term, the forecasts for theAustralian wood supply indicate a stable and growing supply. This means that prices for framingtimber are likely to be more stable for builders in the long term.However, this price stability isquestionable for materials such as steel, which consume considerable amounts of fossil fuels intheir manufacture. The smelting of steel is heavily reliant on the continued availability of cheapsources of fossil fuels, a scenario which is becoming highly uncertain in an increasingly energyand security conscious world. [8;12].

Wood is an environmentally friendly: Wood is the most environmentally responsible buildingmaterial. Wood has low production energy requirements and is a net carbon absorber. Using

wood harvested from sustainable forests makes building with wood an eco-friendly choice.Choosing treated wood that will last for a lifetime also means that you won't need to replace the

product, cutting down on waste. Wood is a natural material, making it an excellent choice forsustainable building. Wood is a renewable resource. Well-managed forests produce timber on asustained continuous basis, with minimal adverse effects on soil and water values. Whetherwood is chosen for its durability or flexibility, looks or low price, wood is the preferred rawmaterial for many homeowners around the globe. [8;12]

Wood is one of the five elements: In Chinese philosophy, things in nature can be classified intofive types: metal, wood, earth, water, fire. In Chinese philosophy, everything we know or thinkof as reality is a symbol, and a reflection of the heavens, so by understanding the macrocosmicrelationship of things we can understand these same relationship on a smaller scale: in the body,in personal astrology, or in politics. [13]

These five elements are therefore not just the materials that the names refer to, but rathermetaphors and symbols for describing how things interact and relate to each other: [13]

Woodis the element of growth and creativity, associated with the spring. It is a masculine element with adark side of anger and depression.

Water is a feminine, flowing element associated with patience and quiet strength, but it can also generatefear with its power.

Fire is a dynamic, masculine element which moves upwards, and it is associated with joy and luck. Whenfire goes bad, it brings about hate.

Earth balances feminine and masculine elements with a tendency to conserve, consolidate, andstrengthen. Anxiety and disquiet are associated with earth imbalances.

Metalis feminine with a contracting energy and the ability to conduct and control emotion. The negativeassociation with metal is grief.

These elements are utilized in several schools ofChinese thought, including feng shui, traditional

philosophy, astrology, traditional Chinesemedicine, and martial arts. Philosophers dedicate

their lives to researching these elements and

their interactions in the hope of learningmore about the intricate and carefully


11/24

balanced systems which make up the universe.[13]

Thinking about the five elements in thetraditional Western sense of elements can beconfusing, because the Chinese view the fiveelements as constantly shifting entities whichcoexist in a cyclical cycle of change and

progression. According to Chinese philosophy,an imbalance in this cycle can lead to problems.Things like feng shui and traditional Chinesemedicine are supposed to identify elementalimbalances and correct or prevent them to keep

people happy and healthy. Chinese philosophydescribes both a production cycle and a controlcycle acting upon the elements: [13]

In the production cycle:[13]

Wood produces FireFire produces Earth

Earth produces MetalMetal produces Water

Water produces Wood

In thecontrolcycle:[13]

Wood controls EarthEarth controls Water

Water controls FireFire controls Metal

Metal controls Wood

The production cycle outlines a pentagon andthe control chain outlines a five pointed star.These interactions and relationships form a

framework for different schools of philosophy.The interaction of five elements becomes a toolthat helps Chinese scholars sort out observationsand empirical data. Based on observations ofhow things interact, things are classified into oneof the five elements so that they fit into theobserved pattern. Then one can draw high levelconclusions or predictions based on the elementtypes. [13]

The five elements feed each other and they canalso consume each other. In the cycle ofgeneration, wood feeds fire which creates earth

in the form of ash, and earth bears metal whichcollects water to nourish wood. In the cycle ofconsumption or overcoming, wood parts earthwhich absorbs water, quenching fire to meltmetal, which chops wood. When these fiveelements or wu xing are in a state of balance, theflow of energy between the elements is smoothand cyclical, rather than static or discordant. [13]

These elements are only a small part of a much larger framework of ideas within Chinese

philosophy. In addition to interacting with each other, the five elements also interact with thingslike locations, people, periods of time, shapes, and colors. Understanding the full complexity ofChinese philosophy as it relates to things like astronomy, tai chi, or acupuncture is usually left tothe experts, although you may hear people making a casual remark so and so has a lot of woodin a reference to the five elements and their associated traits. [13]

Wood is one of the devices of the proxies suggesting the climate patterns of the past: Inmany types of wood, dendrochronology or tree-ring dating (which is the scientific method ofdating based on the analysis of patterns of tree-rings) can date the time at which tree rings wereformed to the exact calendar year. The year-to-year variation in tree-ring widths and isotopic

abundances also gives clues to the prevailing climate at that time. To make inferences aboutwhen a wooden object was created based on the estimated age of organic remains from


12/24

archaeological sites, some wood species can be dated by carbon dating (which is a radiometricdating method that uses the naturally occurring radioisotope carbon-14 to determine the age ofcarbonaceous materials up to about 58,000 to 62,000 years). [14;15].

WOOD: vulnerable behaviour based on the deterioration

The following references were used in the preparation of this section:3,17,18,19,20.

3 Tsoumis, G.T. 1991. Science and technologyof wood (Structure, properties, utilisation).Van Nostrand Reinhold, New York.

17 Eaton E.R.A, and Hale, M.D.C. 1993.Wood: decay, pests and protection.Chapman and Hall Ltd., London.

18 en.wikipedia.org/wiki/Ultraviolet19 informationbible.com/article-how-to-

protect-furniture-at-home-in-hot-summer-78498.html

20 en.wikipedia.org/wiki/Mothball

Wood is biodegradable subject to deterioration by natural agents. In other words, while wood

kept under favorable conditions apparently lasts indefinitely, the most of the wood species arevulnerable which is likely to become endangered unless the circumstances threatening itssurvival and reproduction improve. The principal destroyers of wood are decay, caused byfungus, and attack by a number of animal organisms of which termites, carpenter ants, grubs of awide variety of beetles, teredo, and limnoria are the principal offenders. In addition, fire annuallycauses widespread destruction of wood structures. Decay will not occur if wood is kept wellventilated and air-dry or, conversely, if it is kept continuously submerged so that air isexcluded.[3]

Wood involves moisture because it comes from trees where the cell structure contains excessivewater that makes wood wet. Wood is satisfactory in its natural condition if the moisture available

be dried down to a level consistent with the environment. When wood is used in a location whereits moisture content can range above 20%, wood-inhabiting fungi will probably take upresidence. Termites and carpenter-ant infestations also are encouraged by high moisture content,and some insects are troublesome even in dry wood.[17]

Wood decay is a deterioration of wood by primarily enzymatic activities of microorganisms. Forpractical purposes, fungi are the only agents of wood decay. There are other kinds ofdeterioration, by insects, marine animals, and ultraviolet light (which is electromagneticradiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range10 nm (nanometer) to 400 nm, and energies from 3eV (electron volt) to 124 eV).[18]

Decay: Decay, caused by wood-destroyingfungi, is precluded from wood use except forcertain species in lower grades because thestrength-reducing effects of fungal attack arequite significant even before visible evidence(wood discoloration, punkiness) appears. [3;17]It is important to note that decay organismsrequire moisture to live and grow; hence, the

presence of active decay or mold implies accessto a source of moisture. Moist wood will alwaysdecay, unless the wood is preservative-treated oris of a very durable species. [3;17]

Insect attack: Insect attack may range fromsmall blemishes that do not affect strength tolarge voids or extensive damage in the wood asthe result of termite or other insect infestation.Insect attack is usually treated as equivalent tothe effect of similarly sized knotholes. Mosttermites in the United States are subterraneanand require contact with the soil. The drywoodand dampwood termites found along thesouthern fringes of the country and along thewest coast, however, do not require direct soilcontact and are more difficult to control. Teredo,limnoria, and other water-borne wood destroyersare found only in salt or brackish waters.


13/24

Various wood species vary in natural durabilityand resistance to decay and insect attack. Thesapwood of all species is relatively vulnerable;only the heart wood can be considered to beresistant. [3;17]

Ultraviolet light: Ultraviolet (UV) light isfound in sunlight and is emitted by electric arcsand classified as non-ionizing radiation, it cancause chemical reactions and causes manysubstances to glow or fluoresce.[18]

Many polymers used in consumer products aredegraded by UV light, and need addition of UVabsorbers to inhibit attack, especially if the

products are exposed to sunlight. The problemappears as discoloration or fading, cracking, and,

sometimes, total product disintegration ifcracking has proceeded sufficiently. The rate of

attack increases with exposure time and sunlightintensity. It is known as UV degradation, and isone form of polymer degradation. [18]

In addition, many pigments and dyes absorb UVand change colour, so paintings and textiles mayneed extra protection both from sunlight andfluorescent bulbs (two common sources of UVradiation). Old and antique paintings such aswatercolour paintings, for example, usually must

be placed away from direct sunlight. Commonwindow glass provides some protection byabsorbing some of the harmful UV, but valuableartifacts need extra shielding. Many museums

place black curtains over watercolour paintingsand ancient textiles, for example. Sincewatercolours can have very low pigment levels,

they need extra protection from UV light. [18]

As wood is vulnerable material, product (which is manufactured from wood) requires the care,attention, and rigor necessary to be confident that such goods will not fail. For example; strongdirect sunlight, frequent temperature changes caused by switching air conditioning and excessivedry or humid environment will cause damage to the wood furniture. It will have phenomenon ofdeformation, cracking and bulging. Especially the traditional mahogany furniture with largenumbers of carved patterns is easier to expand with heat and contract with cold, because it

basically has not been dealt on moisture content. No matter the furniture is made of solid wood

or compound materials, they should be protected from damages caused by weather and humidchanges and strong sunlight. People are recommended to adjust the placement of furniture. Theyshould be placed far away from air conditioning and direct sunlight. In the afternoon with intensesunshine, it is better to pull the curtain. In addition, coating a layer of wax on edges of drawerand sliding door could prevent the difficult opening and closing caused by swelling. Put somemothballs (chemical pesticide) in humid areas to prevent the insect effectively, if storing clothingand other articles susceptible to damage from mold or moth larvae (especially common clothesmoths like Tineola bisselliella).[19;20]

WOOD: problems in wood construction

The following references were used in the preparation of this section:9.

9 www.aboutcivil.com/Wood%20as%20construction%20material.html

Wood and wood products are relatively simple engineering materials, but the conception, design,and construction process is fraught with problems and places to err. In using wood in its manyforms and with its unique inherent characteristics, there are problem areas which seem to present

easily overlooked pitfalls. As gentle reminders for caution, some of these areas are discussedbelow. [9]


14/24

Wood and water do not mix well: Wood is hygroscopic and (unless preservative-treated) rotswhen its moisture content (MC) rises above 20%. It must be protected in some way. [9]

Minor roof leakage often leads to pockets ofdecay, which may not be noticed until severe

decay or actual failure has occurred. Stainedareas on wood siding or at joints may indicatemetal fastener rust associated with a wet spot ordecay in adjoining, supporting members. Inmany cases what appears to be a minor problemends up as major and sometimes extensive repairis required. Improper installation or lack of anadequate vapor barrier can result in seriousdecay in studs within a wall as well as paint peelon exterior surfaces. Ground contact of woodmembers can lead to decay as well as providingready access to wood-deteriorating termites.

Placement of preservative-treated membersbetween the ground and the rest of the structure(as a bottom sill in a residence) is usually a coderequirement. [9]

Timber arches for churches, office buildings,and restaurants are usually affixed to a

foundation by steel supports; if the supports arenot properly installed, they may merely form areceptacle for rain or condensation to collect,enter the wood through capillary action, andinitiate decay. Once decay is discovered, majorrepair is indicated; preservative treatment to adecayed area may prevent further decay, but itwill not restore the strength of the material.Elimination of the causal agent (moisture) is

paramount. Visible decay usually means thatsignificant fungal deterioration has progressedfor 1 to 2 feet (approximately 30.5 to 61.0 cm)

along the grain of a member beyond where it isreadily identifiable. [9]

Pay attention to detail: In an area that has high relative humidity, special precautions should betaken. [9]

A structure that is surrounded by trees or othervegetation or that prevents wind and sun from

drying action, is prone to high humidity nearlyevery day, particularly on a north side. Likewise,if the structure is near a stream or other sourceof moisture, it may have moisture problems.Home siding in this type of atmosphere maywarp or exhibit heavy mildew or fungal stain.Buildings with small (or nonexistent) roofoverhangs are susceptible to similar siding

problems if the siding is improperly installed,allowing water or condensation to enter andaccumulate behind the siding. [9]. Inadequatesealing and painting of a surface can add to the

problem. In a classic example, a three-story

home on a tree-shaded area next to a smallstream and with no roof overhang had poorly

installed siding, which subsequently warped sobadly that numerous pieces fell off of the home.Poor architecture, poor site, poor construction

practice, and poor judgment combined to createa disaster. This type of problem becomesmagnified in commercial structures, where largesurfaces are covered with wood panel productsthat tend to swell in thickness at their joints ifthey are not properly sealed and protected fromunusual moisture environments. If properlyinstalled, these materials provide economical,long-term, excellent service. [9]

Wood is viscoelastic and will creep under load: This has created widespread problems incombination with clogged or inadequate drains on flat roofs. Ponding, with increasing roof joistdeflection, can lead to ultimate roof failure. In situations where floor or ceiling deflection isimportant, a rule of thumb to follow is that increased deflection due to long-term creep may beassumed to be about equal to initial deflection under the design loading. In some cases theoccupants of a building will report that they can hear wood members creaking, particularly undera snow load or ponding action. This is a good indication hat the structure is overstressed andfailure, or increasing creep deformation with impending failure, is imminent. Deflectionmeasurements over a several-week period can often isolate the problem and lead to suitable

reinforcement. [9]


15/24

Repair structural members correctly: Epoxy resin impregnation and other techniques areoften used to repair structural members. These methods are said to be particularly effective inrepairing decayed areas in beams and columns. [9]

Removal of decayed spots and replacement by

epoxy resin is acceptable only if the afflictedmembers are also shielded from the originalcausal agent (excess moisture or insect attack).Likewise, if a wood adhesive must be used as afastener in an exposed area, use a waterproofadhesive; water-resistant or carpenters gluewont do.Although several wood adhesives will

produce a wood-to-wood bond stronger than thewood itself, most of these adhesives areformulated for (and used in) furnituremanufacture, where the wood is dry (about 6 to7% MC) at time of fabrication and is presumed

to be kept that way. [9]

Structural-use adhesives (unless they are

specially formulated epoxy or similar types)may be used where the wood is not above about20% MC. Structural-use adhesives must also begap-fillers; i.e. they must be able to form astrong joint between two pieces of wood that arenot always perfectly flat, close-fitting surfaces.In addition, the adhesive should be waterproof.The most common and readily availableadhesive that meets these criteria is a phenol-resorcinol-formaldehyde adhesive, a catalyzed,dark purple-colored adhesive which is admirablysuited to the task. [9]

Protect materials at the job site: Wood, which is subjected to be used as a constructionalmaterial, should be protected from damages caused by weather and humid changes until it isconstructed properly. Wood materials at the job site under excessively humid conditionsneed totake extra precautions, because wood and water do not mix.Failure to do so has caused plywoodand other panel products to become wet through exposure to rain so that they delaminate, warpseverely, or swell in thickness to the point of needing to be discarded. [9]

Lumber piled on the ground for several days or

more, particularly in hot, humid weather, willpick up moisture and warp or acquire surfacefungi and stain.This does not harm the wood ifit is subsequently dried again, but it does renderit esthetically unfit for exposed use. [9]

Make sure that panel products, such as plywood,

OSB, or flakeboard are kept under roof prior toinstallation. Stacked on the ground or subjectedto several weeks of rainy weather, not only willthese panels warp, but they may lose theirstructural integrity over time. [9]

Take time to know what species and grades of lumber you require, and then inspect it:

Engineers and architects tend to order the lumber grade indicated by mathematical calculations;carpenters use what is provided to them. Unlike times past, no one seems to be ultimatelyresponsible for appropriate quality until a problem arises and expensive rework is needed. [9]

Case in point: a No. 2 grade (American Lumber Standard Committee)2-by (which is tacitly presumed tobe used in conjunction with other structural members to form an integrated structure) is not satisfactoryfor use as scaffolding plank or to serve a similar, critical function on the job site where it is subjected tolarge loads independent of neighboring planks. [9]

Inspect the wood quality based on the tree growth: As the old saying goes, an ounce ofprevention is worth a pound of cure. Be aware of wood and within-grade variability due to theuniqueness of tree growth and wood defects. [9]

It is often wise to screen lumber to cull outpieces that have unusually wide growth rings orwood that is from an area including the pith(center) of the tree.This material often tends to

shrink along its length as much as ten times thenormal amount due to an inherently highmicrofibrillar angle in growth rings close to the

pith. [9]


16/24

In truss manufacture this has resulted in thelower chords of some trusses in a home (lowerchords in winter being warmer and drier) toshorten as they dry, while the top chords do notchange MC as much. The result is that the trusswill bow upward, separating by as much as aninch (2.54 cm) from interior partitions (verydisconcerting to the inhabitants and very

difficult to cure). A good component fabricatoris aware of this phenomenon and will buyhigher-quality material to at least minimize the

potential problem. Conversely, avoid theexpensive, cover all the bases approach ofordering only the top grade of the strongestspecies available. [9]

Inspect all timber connections during erection: Check on proper plate fasteners on trusses andparallel chord beams after installation; plates should have sufficient teeth fully embedded intoeach adjoining member. [9]

Occasionally in a very dense piece the metalteeth will bend over rather than penetrate intothe wood properly. A somewhat similar problemarises if wood frames or trusses are not handled

properly during erection; avoid undue out-of-plane bending in a truss during transport orerection since this will not only highly stress thelumber but may also partially remove the platesholding the members together. [9]Bolted connections must be retightened atregular intervals for about a year after erectionto take up any slack due to subsequent lumber

drying and shrinkage.Perhaps one of the majorcauses of disaster is the lack of adequate bracingduring frame erection. This is a particularlyfamiliar scenario on do-it-yourself projects, such

as by church groups or unskilled erection crews.Thin, 2-by lumber is inherently unstable in longlengths; design manuals and warning labels onlumber or product shipments testify to this, yetthe warnings are continually disregarded.Unfortunately, the engineer, designer, orarchitect and materials supplier often are madeto share the resulting financial responsibility. [9]

Be aware of woods orthotropicity: A large slope of grain around a knot or a knot strategically

poorly placed can seriously alter bending or compressive strength and are even more limiting intension members. Allowable design values for tension parallel to the grain are dictated by anASTM (American Society for Testing and Materials) standard (i.e. as being 55% of allowable

bending values because test results have indicated that slope of grain or other defects greatlyreduce tensile properties). Different orthotropic shrinkage values, due to grain deviations orimproper fastening of dissimilar wood planes, can lead to warpage and subsequent shifts in load-induced stresses. Care must be taken when using multiple fasteners (bolts, split rings, etc.) toavoid end splits as wood changes MC, particularly if the members are large and only partiallydried at the time of installation. [9]

When installing a deep beam that is end-supported by a heavy steel strap hanger, it is often best

to fasten the beam to the hanger by a single bolt, installed near the lower edge of the beam. Thiswill provide the necessary restraint against lateral movement, whereas multiple bolts placed in avertical row will prevent the beam from normal shrinkage in place and often induce splits in theends of the beam as the beam tries to shrink and swell with changes in relative humidity. Notonly are the end splits unsightly, but they also reduce the horizontal shear strength of the beam ata critical point. In addition, if the beam has several vertically aligned bolts and subsequentlyshrinks, the bolts will become the sole support of the beam independent of the strap hanger, asshrinkage lifts the beam free of the supporting strap hanger. [9]

Use metal joist hangers and other fastening devices (they add strength and efficiency in

construction to a job): Toe-nailing the end of a joist may restrain it from lateral movement, but

it does little to prevent it from over turning if there is no stabilizing decking. Erection stresses


17/24

caused by carpenters and erection crews standing or working on partially completed frameworkare a leading cause of member failure and job site injury. [9]

In renovating old structures, as long as decay isnot present, the old members can be reused.

However, because large sawn timbers tend tocrack as they dry in place over a period of time,the members must be regraded by a qualifiedgrader. [9]

The dried wood (usually well below 19% MC)has increased considerably in strength, perhaps

counter balancing the decrease in strength due todeep checking and/or splitting. End splits oversupports should be carefully checked for

potential shear failure. [9]

Wood and fire pose a unique situation: Wood burns, but in larger sizes (i.e. 15 cm (6 inch) andlarger) the outer shell of wood burns slowly and (as the wood turns to charcoal) the wood

becomes insulated and ceases to support combustion.Once the fire has been extinguished, thewood members can be removed, planed free of char, and reused, but at a reduced sectionmodulus. Smaller members can also be fire retardanttreated to the degree that they will notsupport combustion. However, treating companies should be consulted in regard to any possiblestrength-reducing effects due to the treatment, particularly where such members are to besubjected to poorly ventilated areas of high temperature and high relative humidity, as in atticspaces. In recent years newly developed fire retardant treatments have reacted with wood whenin a high temperaturehigh relative humidity environment to seriously deteriorate the wood intreated plywood or truss members. These chemicals, presumably withdrawn from themarketplace, act slowly over time, but have contributed to structural failure in the attics ofnumerous condominium-type buildings. [9]

Preventive measures where such problems maybe anticipated include the addition ofthermostatically controlled forced-air venting(the easiest and probably most effective

measure). The addition of an insulation layer tothe underside of the roof to reduce the amount ofheat accumulation in the attic due to radiant heatabsorption from the sun. The installation of avapor barrier on the floor of the attic to reducethe amount of water vapor from the underlyingliving units. [9]

In using preservative-treated wood, it is alwaysbest (certainly so when dealing with largermembers) to make all cuts to length, bore holes,

cut notches, etc., prior to treatment. Depth ofpreservative treatment in larger members isusually not complete, and exposure of untreatedmaterial through cutting may invite decay.Determination of the depth of penetration of a

preservative by noting a color change in thewood is hazardous; penetration may be more orless than is apparent to the eye. Deep checkingas a large member dries will often exposeuntreated wood to fungal organisms or insects.

Periodic treatment by brushing preservative intoexposed cracks is highly recommended. [9]

This is particularly true for log hometype

construction. Modern log home constructionutilizes partially seasoned materials with shapedsections, which not only increase the insulativequality of the homes but also tend to balance, orrelieve, shrinkage forces to reduce cracking.Treated or raised nonwood foundations arerecommended. [9]

Wood is an excellent construction material,tested and used effectively over the years for a

myriad (an unspecified large quantity) ofstructural applications provided one takes thetime to understand its strengths and weaknessesand to pay appropriate attention to detail.Knowing species and lumber gradecharacteristics and how a member is to be used,not only in a structure but also during erection,can go a long way toward trouble-freeconstruction. [9]


18/24

WOOD: treatment against biodegradation

The following references were used in the preparation of this section:2,17,21,22,23,24,25.

2 Hoadley, R.B. 1980. Understanding wood(A craftman`s guide to wood technology).

The Taunton Press, Inc., London.

17 Eaton E.R.A, and Hale, M.D.C. 1993.Wood: decay, pests and protection.Chapman and Hall Ltd., London.

21 www.aboutcivil.com/Decay%20and%20preservation%20of%20wood%20timber.html

22 en.wikipedia.org/wiki/Wood_preservation

23 Hiziroglu, S. 2009. Basics of pressuretreatment of wood. Oklahoma State

University, Oklahoma CooperativeExtension Fact Sheets, Natural ResourceEcology and Management, NREM-5047.(http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2531/NREM5047web%20color.pdf).

24 en.wikipedia.org/wiki/Sodium_tetraborate25 en.wikipedia.org/wiki/Boron

Although environmentally friendly and renewable wood material has been used extensively inindustry, it poses major problems when exposed to fungi, insect and termite activity.Biodegradation of wood is accomplished in part by insects and marine borers, but the greatestdegree of deterioration is the work of wood-inhabiting fungi. Wood is usually deteriorated byfungi (white rot, brown rot, dry rot, soft rot fungi), insects (termites, beetles, carpenter ants),marine borers (molluscans, crustaceans), and a host of other agents. Wood preservation

protecting wood, wood products or timbers from deterioration, decomposition or damage due topest attacks through application of chemical substances. [17]

Certain wood species have heartwood extractives that resist the attack of fungi and are termeddecay-resistant or durable woods, and certain woods have selective resistance to insect attack. In

many cases, however, where conditions favorable to biological deterioration cannot be avoided,and where resistant species are not available, the best alternative may be to treat the wood with asubstance that will give it the desired durability. Such chemicals are called wood preservatives(i.e. this term sometimes includes treatments to make the wood nonflammable, although the termfire-retardant is preferred for such materials).[21]

The ideal preservative would readily penetrate the wood and would be permanent, toxic to fungiand insects, safe to handle, colorless, compatible with coatings and finishes, and of course,inexpensive. No one chemicals has yet been developed that has all of these attributes, but a widearray of chemicals with various advantages have emerged for specific purposes.[21;22]

For all practical purposes only a few nativespecies are truly immune to fungal deterioration,and then, as stated earlier, only the heartwood

portion of the wood is decay-resistant.Availability and economy usually dictate thatwhere decay resistance is required, preservativetreatment is a must. Any structural componentthat is in contact with the ground, subject to

periodic wetting (leakage or rain), or in a high-relative-humidity atmosphere for extended time

periods, may be expected to decay. There areseveral preservatives available; degree of

exposure and the use of the member willindicate which specific preservative to use. In all

cases a pressure treatment is required; diptreating, soaking, or painting the surface with a

preservative solution are only temporarydeterrents at best and are not recommendedwhere structural integrity is required. [21]

The key to using preservatives is penetration.Only areas of the wood that are penetrated by

preservative chemicals will be protected.[22]

A first consideration, then, is choosing the mostpenetrable wood.Generally, sapwood or species

with low extractive content (ironically those thatusually have the least natural decay resistance)


19/24

are the best choice for preservative treatment.Except for very thin pieces, the only way toattain any worthwhile degree of penetration isunder pressure. Commercially, this is done usingcylinders that produce pressures up to about 150

psi, and sometimes also with vacuum treatmentor elevated temperatures.Since such conditionsare beyond the capability of the averagewoodworker, it is usually most logical to buy

commercially treated lumber for use whereconstant moisture problems prevail. [22]

No single preservative is available which canmeet all desirable requirements. Wood

preservatives may be oil-borne, water-based or amixture of different substances. Preservative-treated structural lumber is available in severalgrades, depending upon intended use andretention level. [22]

The life of preservative-treated timber products depends on penetration, retention and degree offixation of preservatives used. The penetration and retention of a preservative, however, dependson the preservation method. The different wood protection methods being used in worlwideeither using pressure or non-pressure (including with washing and coating, brushing, sprayingand dipping, soaking, Boucherie process, hot and cold bath process, diffusion process). [17;22]

Pressure wood treatment: The purpose of wood pressure treatment is to force preservativechemicals deep into the cellular structure of the wood. The chemical acts as a barrier between thewood and biological deterioration agents, so that the service life of the wood can be substantiallyincreased.[23]

Pressure treatment methods are classified intotwo basics groups: full-cell and empty-cell

processes. [23]

In the full-cell method, both cell wall and lumen

are filled with the preservative solution, whilethe objective of empty-cell process is to retain

preservative chemical in only the cell wall.Thefull-cell method is the oldest treatment processand is the best for the highest penetration andretention of preservative. [23]

In the ful-cell process, air inside the wood isremoved by initial vacuum and then empty cellsof woods are filled up with preservativechemical by applying pressure. The full-cellmethod is generally used where a large amount

of preservative is needed for certain applicationssuch as treatment of utility poles, farm fence,

bridge timbers, and pier timbers. This processresults in high retention, but not necessarilydeeper penetration than that of other processes.[23]

Preservative chemicals used for the pressure treatment process can be classified into threegroups: tar oil based, oil-borne, and water-borne preservatives. [23]

Oil-borne preservatives: Creosote and pentachlorophenol (PCP) are the organic oil-basedpreservatives, earlier used for treating of wood poles, piles and railway sleepers. Nowadayscreosote is used only for railway ties. [23]

One of the oldest and most effective treatments,is creosote that is used primarily for treatingutility poles and marine piling. It is often calledcoal tar creosote because of its close relationshipto toluene, benzene, and tar. These materials arecondensed from the distillation of coal as it isconverted to carbon. It is an oil-borne

preservative of high toxicity and is notrecommended where human contact isanticipated. [23]

Creosote penetrates deep into and remains in thewood for a long time. Exposure to creosote may

be harmful to humans and special precautionsshould be taken for handling creosote-treatedwood products. [23]Creosote can be successfully used for farm,fence, and other outdoor building materials.Coaltar creosote has been used commercially to

preserve such things as railroad ties and utility


20/24

poles. However creosote should not be used forthe interior of farm buildings. [23]

An oil borne preservative, pentachlorophenol(PCP) is also widely used to treat wood

products. PCP-treated wood can be used for

commercial interior applications except forlaminated beams or as construction componentwhere a direct ground contact exists. In a typicalapplication, the surface of the treated laminated

beam should be coated with a sealer. [23]

Water-borne preservatives: Arsenic and copper-based preservatives, such as ammoniumcopper zink arsenate (ACZA), ammoniacal copper arsenate (ACA), chromated copper arsenate(CCA), and copper naphthenate are water-borne preservatives which have been used extensively

by the wood processing industry for many years. [17;22;23]

CCA (chromated copper arsenate):Chromated copper arsenate (CCA) is consideredas effective inorganic water-based preservativeand is being used for treating electric wood

poles, anchor logs and corsairs. A number ofarsenic containing treatments are commonlyused. CCA (chromated copper arsenate) is usedwith dimension lumber, particularly withsouthern pine, and ACA (ammoniacal copperarsenate) is also commonly used. Both CCA andACA are waterborne preservatives that are

pressure-impregnated into dry (below fibersaturation point) lumber; the chemicals become

permanently bonded to the wood as the wood

becomes redried after treatment. It is veryimportant to know that until the wood hasbecome dry again after treatment, it is dangerousto handle. Resawn wood that is wet on the insideof the piece, even if it appears dry on theoutside, can produce arsenic poisoning.[17;23]

It is also important to know that even under highimpregnation pressures, the depth of penetrationof the preservative into the wood may beincomplete. Resawing may expose untreatedwood to decay; treatment after cutting or boring

members to final size is recommended. CCAand ACA treatments are commonly used forfoundations, decks, and greenhouses. Dry CCA-treated and ACA-treated lumber is approved forhuman contact use. [17;22;23]

Under no circumstances are wood scraps ofCCA-treated or ACA-treated wood to be burnedin the open air; this will ultimately release

poisonous arsenic and chromium compoundsinto the air. Borate compounds are effectivewood preservatives and are economical and

nontoxic to humans and animals. Unfortunately,they also leach out of the wood rather readily

when subjected to rain or wet conditions.Research on these and other compounds mayresult in a new family of leach-resistant,nontoxic-to-humans preservatives for wood inthe future. [23]

Preservative companies producing CCA, whichis one of the most commonly used preservativeson the market, have requested the cancellation ofthat product for certain uses due to possiblehealth concerns. The Environmental ProtectionAgency in USA has accepted this request and asof December 31, 2003 no wood will be treatedwith CCA for residential uses such as decking,

playground, and constructional purposes.However, CCA will still be used for non-residential application. Similar to PCP andcreosote, arsenic-based chemicals are also

poisonous. Special precautions stated on theconsumers safety information label should befollowed closely. [23]

Chromated copper boron (CCB): Apreservative containing Cr (chromium), Cu(copper), and B (boron) (namely, CCB:chromated copper boron) is another water-borne

preservative, used for indoor use such as forelectric meter boards, wooden packings, doorsand windows, furniture etc. In its formulation, itis considered to be less toxic than the mostwidely used water-borne preservative CCA(because of the absence of arsenic), but it also isconsidered to be less effective because of thehigh leaching of boron. Leaching of preservativecomponents may take place at different ratesdepending of a number of factors, such as thewood species, the surface area exposed, the

preservative retention, and the local

environmental conditions. [22;24]


21/24

In addition, leaching of metals is notproportional to their initial retention in wood.CCB may be as effective as CCA in sites wheretemperate climatic conditions with long dry

periods are dominant. [24]Boron is a chemical compound (with a purechemical substance consisting of two or moredifferent chemical elements) that can beseparated into simpler substances by chemicalreactions. [25]

Borax (also known as sodium borate, sodiumtetraborate, or disodium tetraborate) is animportant boron compound, a mineral and a saltof boric acid. It is usually a white powderconsisting of soft colorless crystals that dissolveeasily in water. Borax has a wide variety of uses.

It is a component of many detergents, cosmetics,and enamel glazes. It is also used to make buffersolutions in biochemistry, as a fire retardant, asan anti-fungal compound for fiberglass, as an

insecticide, as a flux in metallurgy, a texturingagent in cooking, and as a precursor for other

boron compounds. [25]

Boron compounds (such as borax, boric acid,boric oxide and borate salts) are effective woodpreservatives and are supplied under numerousbrand names throughout the world. Boratetreated wood is of low toxicity to humans, anddoes not contain copper or other heavy metals.However, unlike most other preservatives,

borate compounds do not become fixed in thewood and can readily be leached out. Thereforethey should not be used where they will beexposed to rain, water or ground contact. Recentinterest in low toxicity timber for residential use,along with new regulations restricting some

wood preservation agents, has resulted in aresurgence of the use of borate treated wood forfloor beams and internal structural members.[25]

Non-pressure wood treatment: Non-pressure treatments include soaking, dipping and brushapplication. For any use involving contact with the soil or constantly wet or moist conditions,such as fence posts or sills lying on bare ground, nothing less than immersion in preservative forseveral days will be worth the expense and effort. The wood should be at least air-dried tofacilitate penetration and to ensure that no further drying occurs after penetration, which might

open checks and thus expose untreated wood. [2]

Hot and cold baths: Where possible to do so safely, heating the preservative solution willimprove penetration. Heating the wood expands and drives out air from the cell structure; whenallowed to cool, the remaining air contracts, drawing the preservative solution into the cellstructure. Cutting open test pieces indicates the degree of penetration. Chemical indicators areavailable for determining the penetration of colorless materials. [2]

Superficial treatment: Brush and dip methods give only superficial treatment and should berelied upon only where the wood needs surface protection, as with above-ground parts of astructure exposed to intermittent rainfall. Dip treatments (total immersion for a few minutes) will

do a far beter job than brush treatment of reaching vulnerable voids such as bolt holes, deep endchecks, splits and loose knots. Dipping or flooding the surface may give fairly good end

penetration, but side-grain penetration by either method may be as little as 0.8 mm varyingsomewhat according to species. [2]

The most common mistake in using surface treatments is application after rather than before construction.Consider an outdoor structure such as a deck, porch, bench, boardwalk, railing or flower trellis. During arain, water seeps and settles into joints and crevices and is absorbed by the wood, especially intoconcealed end-grain surfaces, such as the bottom ends of vertical posts resting on horizontal surfaces.After the rain, most exposed surfaces, especially side-grain surfaces, dry quickly enough that fungalactivity does not make significant progress. In hidden joints, water is held longer, absorption is prolongedand drying is delayed. The hidden surfaces of joints are therefore the most vulnerable places. These

places are seldom reached by preservative brushed on after construction. For this reason, every effortshould be made to apply preservative to bolt holes, joint surfaces and inside mortises before assembly. In


22/24

nailing exposed horizontal surfaces, such as deck boards or stair treads, nail heads should be driven inflush. Setting nails below the surface exposes end grain and creates a water pocket. [2]

The superficial brush treatment can nevercompensate for poor design. For exteriorapplication, promoting runoff and preventingentrapment of water should be primaryconsiderations. Many modern fungicidal

preservatives are both water-repellent andfungicidal. They are called water-repellent

preservatives anda re-marketed as such. [2]

In combination with good design, brushapplication of these preservatives can be quiteeffective. Remember, however, that no brushed-on preservative will last forever. The chemicalitself eventually leaches out of the wood

becomes diluted or simply degrades afterprolonged exposure to the weather. Thisdeterioration takes place from the exposedsurfaces inward, another reason why depth of

penetration is so important. [2]

WOOD: epilogue

The following references were used in the preparation of this section:2,3,8,11,23,26.

2 Hoadly, R.B. 1980. Understanding wood (Acraftman`s guide to wood technology). TheTaunton Press, Inc., London.

3 Tsoumis, G.T. 1991. Science andtechnology of wood (Structure, properties,utilisation). Van Nostrand Reinhold, NewYork.

8 www.aboutcivil.com/Properties%20of%20Wood%20and%20Timber.html

11 www.askfactmaster.com/Wood23 Hiziroglu, S. 2009. Basics of pressure

treatment of wood. Oklahoma StateUniversity, Oklahoma CooperativeExtension Fact Sheets, Natural ResourceEcology and Management, NREM-5047.(http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2531/NREM5047web%20color.pdf).

26 http://www.kramers.org/whywood.htmlWood is a material found as the primary content of the stems of woody plants, especially trees,

but also shrubs. These perennial plants are characterised by stems that grow outward year afteryear, and that are composed of cellulose and lignin based tissue. Plants that do not produce woodare called herbaceous, i.e. this group of plants includes all annual plants, many perennial plants,and most submerged and floating aquatic plants. The woody tissue is formed by the plant forstructural purposes, and because it is an effective and efficient structural material, it is useful tohumans. Wood is made of cellulose fibers, held together with lignin. Wood that is broken downinto fibers is called pulp, which may then be made into paper. Artists and craftsmen shape and

join pieces of wood with special tools, which is called woodworking or carpentry.[ 11]

Wood is the oldest material used by humans for construction after stone. Despite its complexchemical nature, wood has excellent properties which lend themselves to human use. [8]

Structurally it is easily machinable.Exceptionally strong relative to its weight.A renewable and biodegradable resource.Readily and economically available.Clearly it is a good heat and electrical insulator.Has a natural charm and beauty.

Wood is amenable to fabrication into an infinitevariety of sizes and shapes using simple on-site

building techniques.Originally it has a vulnerable behaviour.Our ancestors used wood as the primary materialthrough the development of civilizations.Due to structural issues, its allure for customer isincreasing importance.


23/24

Wood has been an important construction material since humans began building shelters, andremains in plentiful use today. However, wood has some drawbacks of which the user must beaware. The major problems that arise in wood use may be attributed either to the effects of graindistortions (cell orientation or alignment), to the effects of excess moisture, or to defects thatoccur as a result of the drying process. The specific defects taken into account in the grading of

lumber products include knots, slope of grain, wane, shake, splits and cracks, insect attack, anddecay. [11]

Wood is a natural material and is available inlimited amount. The woodworker finds thatwood is satisfactory in its natural condition formost uses, requiring only that the moisture orsap be dried down to a level consistent with theenvironment. [2]

When cut down and dried, wood is used formany different purposes. [11]

Wood is an excellent renewable buildingmaterial. However, when a wood product is used

in contact with the ground or exposed to highmoisture conditions it may be subjected to

biological and insecticidal deterioration. [3]

As a result of termite or fungi attack, wood frommost species can be destroyed within five toeight years. To extend the service life of wood to20-25 years in moist environmental conditions,it is important to use pressure treatmentmethods.[23]

One of the first things we must remember is to use each wood to its best purpose. Until thiscentury wood was the single greatest material aid and comfort in every century of our ancestorslives. Wood is the most important material contact we have with the entire body of our ancestry.It has been paramount in aiding, comforting and paving the road to civilization.[26]

Wood is the natural material that positively benefits the planet and our relationship to it. Weshould therefore explore as many ways of using it in our daily life as possible.

REFERENCES

1 http://en.wikipedia.org/wiki/Tree2 Hoadley, R.B. 1980. Understanding wood (A craftman`s guide to wood technology). The Taunton

Press, Inc., London.

3 Tsoumis, G.T. 1991. Science and technology of wood (Structure, properties, utilisation). VanNostrand Reinhold, New York.

4 http://en.wikipedia.org/wiki/Wood5 http://en.wikipedia.org/wiki/Timber6 http://en.wikipedia.org/wiki/Lumber7 http://www.matbase.com/material/wood/8 http://www.aboutcivil.com/Properties%20of%20Wood%20and%20Timber.html9 http://www.aboutcivil.com/Wood%20as%20construction%20material.html10 http://findarticles.com/p/articles/mi_m3575/is_1281_213/ai_111268372/11 http://www.askfactmaster.com/Wood12 http://ezinearticles.com/?Wooden-Deck-Boards---5-Reasons-Why-Wood-is-the-Best-Material-

For-Decking&id=4441832

13 http://www.askfactmaster.com/Five_Elements


24/24

14 http://en.wikipedia.org/wiki/Dendrochronology15 http://en.wikipedia.org/wiki/Radiocarbon_dating16 http://www.essayclub.com/term-papers/Wooden-Chopsticks/2719.html17 Eaton E.R.A, and Hale, M.D.C. 1993. Wood: decay, pests and protection. Chapman and Hall

Ltd., London.18 http://en.wikipedia.org/wiki/Ultraviolet19 http://informationbible.com/article-how-to-protect-furniture-at-home-in-hot-summer-78498.html20 http://en.wikipedia.org/wiki/Mothball21 http://www.aboutcivil.com/Decay%20and%20preservation%20of%20wood%20timber.html22 http://en.wikipedia.org/wiki/Wood_preservation23 Hiziroglu, S. 2009. Basics of pressure treatment of wood. Oklahoma State University, Oklahoma

Cooperative Extension Fact Sheets, Natural Resource Ecology and Management, NREM-5047.(http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2531/NREM

5047web%20color.pdf).24 http://en.wikipedia.org/wiki/Sodium_tetraborate25 http://en.wikipedia.org/wiki/Boron26 http://www.kramers.org/whywood.html

IRG 12-40583_R_USTA_2012_wood in life.pdf

Documents

Transcript of IRG 12-40583_R_USTA_2012_wood in life.pdf