Moisture Problems, Helpful Hints and Moisture Meters.

Contents: page

Common Moisture Problems...... 1Why Moisture Problems Occur.. 1Shrinking and Warping.............. 1The Perfect Board.................... 2A Cure? Prevention!................. 2Common Causes for Porblems 2Moisture Meters....................... 2Helpful Hints........... ............... 3Finding the Right Moisture ........ 4Concrete ................................ 4Relative Humidity Table ........... 4

Year Rings: Each board has a unique year ring pattern (grain),dependent upon its position in the log.

Shrinkage and warpage vary with wood moisture and with thearrangement of year rings. See also “The Perfect Board” page 2and “Selecting a Wood Species” page 3.

Shrinkage: Whenever wood below Fiber Saturation Point loosesmoisture, it shrinks. By actually measuring the shrinkage in a blockof wood, it has been found that shrinkage is not uniformly the samein all directions, but differs with the grain. Tangential shrinkagealong the year rings is twice as much as radial shrinkage acrossthe year rings. The different shrinkage factors within the sameboard cause warpage by pulling the board in different directions.

1a 1b

1a) Arrows indicate radial shrinkage1b) Arrows indicate tangential shrinkage

1c) Quarter sawn board with straightyear rings parallel to the edges

1c

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Wood is an ideal raw mate-rial: long lasting, sturdy, easy toshape, join together or glue andcontinuously renewed. Above all,wood is beautiful. Everybody likesits durability, texture, looks, touch,color and unique design. Wood is used in many differentapplications - from structuralbuilding components to hard-wood flooring, from furniture totoys for kids, from cabinets tomusical instruments.

The challenge of utilizing woodstarts with choosing the right wood. If wood is not right for theapplication, the best machining and excellence in workmanship can-not guarantee a high quality product. Wood species, grade andmoisture content determine quality and usefulness of wood.

Common Moisture Problems are...

A chair with loose joints or a cabinet door that will not close. Abutcher-block table with a big crack down the middle or a veneeredsurface that shows surface checks. Edge banding applications wherethe glue line fails. A jewelry box with crooked joints and bent out ofshape or cupped or crowned floors and foggy finishes.

Hardwood Floors present a special challenge. Small moistureproblems in floor planks, subfloor and the concrete underneath canadd up to big defects - plank by plank .

Moisture defects are irreversible. Immense stress within the woodpermanently deforms or destroys the structure of the wood (crack-ing, checking, warping, honeycombing).

Why Moisture Problems Occur

Wood is not a homogeneous material, but structured by yearrings, which form a series of more or less concentric cylinders.These cylinders consist of irregular tubes that transport nutrientsand support the tree. Interaction with Air: When wood absorbs or looses moisture be-low the Fiber Saturation Point (28%-35%), the tubes expand orcontract, causing wood to swell or shrink. To make matters worseshrinking and swelling is often accompanied by warping. Shrink-ing does not occur lengthwise along the tubes.

Changes in the wood moisture content occur until an equilib-rium with the surrounding air has been reached. At that point theequilibrium moisture content (EMC) of air is the same as the woodmoisture content (MC).

If wood pieces with different moisture contents were placed fora long time in a constant climate of 700F and 35% relative humidity,all wood would end up with a moisture content of 6% independentof the wood species or the initial moisture content.

Since 700F and 35% - 45% relative humidity represent normalin-home conditions, hardwood floors and furniture built with a mois-ture content of 6-8% is dimensionally stable, see chart on page 4.

Shrinking and Warping

Shrinkage between 18% and 6% in Red Oak.At the beginning of the test both pieces ( 1 1/4” x 4”) had thesame size and the same moisture content of 18%. The upperpiece dried down to 6%, whereas the lower piece was kept at the18% moisture level.

Printed by Lignomat USA Ltd August 08 C

Warpage: In most cases shrinking is accompanied by warping.Warpage deforms boards by cupping, crowning, bowing, twisting ora combination of all four.

2a

2b

2a) Twisting: Curved diagonally across the board2b) Bowing: Curved along the length of the board2c) Cupping: Curveddownwards along the width of the board

Crowning: Curved upwards along the width of the board

2c

The drawings above indicate the main deformations of a board. Forinstance, when a wood floor gets excessively wet the floor planksabsorb extra moisture and swell. Since there is not much room toexpand problems become obvious very fast.

1c)quarter sawn boards

1a,b)assymetric boards

The Perfect Board....Has straight year rings parallel to its edges. See page 1, quartersawn board fig. 1c. When changes in moisture occur, these boardsswell or shrink the least and do not warp. Ideal for solid applica-tions, where humidity and temperature changes year around suchas entrance ways.

Trees grow crooked and year rings are often distorted. Thesenatural irregularities make it hard to find the “perfect tree”. In addi

tion, only a small number of quarter sawn boards can be cut out ofa tree. Therefore, quarter sawn boards are rare and expensive.

Moisture Defects: Is there a Cure or only Prevention?Everybody who has lived in a home with hardwood floors

knows that small cracks appear and disappear with the changesof the seasons. Caused mainly by changes in relative humidityoutside these minor changes can be avoided with controlledambient conditions inside.

If floor planks are not dry at the time of installation or ab-sorbed extra moisture later on, the floor will show real defects. Insome cases the floor can be repaired by resanding and refinish-ing, but only after it has been confirmed that the floor is dry now.

If the defects are so severe that permanent damage to thestructure of the wood has occured, there is no cure. The floorhas to be replaced. Therefore, moisture problems have to beavoided before they occur. Make sure the floor is dry before instal-lation. One wrong board can be enough to ruin a floor, and you endup with a lot of disappointment and complaints.

Common Causes for Moisture Problems in Wood Floors- Floor Planks were not dry at the time of installation- Subfloor was too wet- Existing or new concrete floor was not dry enough- Water spills or leaks- Ambient conditions see graph on last page

Moisture MetersThe main criteria when selecting a moisture meter is moisturerange (dry or green wood) and measuring depth (thin or thickboards). Two types of meters are available, with pins and withoutpins. In general pin meters are more versatile, they are also moreaccurate when measuring differences between surface and coremoisture. Pinless meters are convenient and leave no pin holes.however for a finished floor a pinless meter may be your only op-tion.

Popular, low cost mini-Ligno E/D

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Using the Pin Meter: mini-Ligno DX/C with Electrode E12The mini-Ligno DX/C can be accurately adjusted for measuringdifferent woods by selecting one of 20 wood groups. A chart comeswith each meter listing domestic and tropical wood species andthe corresponding wood groups. The DX/C comes with integralpins and can be used without the electrode. Just press the pins inthe wood and obtain a measurement.

For a more thorough check measure the endgrain on a freshcut. The meter measures a small area and thus can be used todetect differences between core and surface. The meter is alsosuited to measure subfloors.

The Slide Hammer Electrode allows easier penetration of thewood and allows checking an existing subfloor without removingthe floor planks. As you hammer the insulated pins of the Elec-trode E12 through the floor and subfloor you can see if moistureproblems are coming from above or below the floor.

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Professional Meter Package D-2M: DX/C with E12

Using the Pinless Meter: Ligno-Scanner SDAll of Lignomats Scanners give true moisture reading in percentand can be set to read any wood with a specific gravity between 0.3and 1.0. Lignomat supplies a wood species chart that lists thesettings for many domestic and tropical wood species. In addi-tion, the Internet supplies specific gravity values for most species.

Ligno-Scanner SD: This unique meter with its two selectablemeasuring depths of 1/4” or 3/4” is very useful for the floor installer1/4” : -check waterborne finishes between applications

-check surface layer of engineered floors-check flooring close to the surface-check thin floor strips

3/4”: -check floor planks for average dryness-check engineered or bamboo floors by comparing to a drysample and determine a setting for future reference

-check subfloors

Ligno-Scanner SD

Helpful Hints

Buying Flooring: Upon delivery, check the moisture contentwith a moisture meter. In case the floor does not have the expectedmoisture content, notify the supplier promptly. If you wait too long,the supplier may not accept the claim.

Selecting a Wood Species: Not all woods shrink the same.Teak, Mahogany, Cedar, Sugar Pine, Mesquite and Redwood aredimensionally stable woods. Oak, Beech and Hickory shrink con-siderably more, see photo on page1. Unfortunately, more shrink-ing is always accompanied by more warping. In entrance-ways orkitchens and bathrooms, it may be advisable to choose more stablefloor planks of a higher grade to avoid problems.One rule applies to all floor boards: The more parallel the grainruns to the edges of the board, the less shrinkage and warpagecan be expected. ( See page 2, The Perfect Board.)

Expertise: Follow the NWFA Installation Instructions. And yourexpertise, the right material and the right tools should guarantee afloor with lasting beauty.

Proper Storage: All floor planks must be stored in a closed-inarea with a controlled climate. If stored in a damp place, the drywood will pick up moisture from the air.

Lignomat offers Thermo-Hygrometersto measure relative humidity and tempera-ture in a warehouse, workshop or otherstorage areas. Thermo-Hygrometers arealso useful to check conditions inside yourhome, office or showroom.

A complete diagram of the relation-ship between-Temperature-Relative Humdity andEMC is available from Lignomat. For apartial chart see page 4.

At 700F and 35% relative humidity the EMC is 7% - ideal conditions.

At 850F and 75% relative humidity the EMC is 14% - moist summer.

At 320F and 20% relative humidity the EMC is 5% - dry winter.

Finding the Right Moisture ContentThe graphs on this page show that the moisture content dependsupon the climate in a region. There are big differences in averagerelative humidity and temperature between the high desert in Colo-rado and the moist, tropical climate in Florida.

To determine what is the right moisture content for your floor,measure the moisture in furniture and floors that have been in-stalled in your house or office “forever”. These old pieces havereached the Equilibrium Moisture Content with the surrounding air.

Are you concerned about climate changes throughout the year?Measure the same floor section in your home, shop or office onceevery month. After 12 months you have a series of moisture valuesthat reflect seasonal changes. You may be amazed how little thewood moisture changes inside your home.

ConcreteAfter studying the NWFA Installation Manual, the first myth that

will be erased is, that a non-invasive scan meter can be used todetermine if the concrete is dry enough to put a wood floor down.All experts agree, that resistance and surface electrical imped-ance meters should not be used for that purpose.

We recommend the RH method following ASTM F-2170 forchecking the concrete. The RH method measures moisture notonly at the surface but in the “core” of the concrete. It is a knownfact that in wood the surface dries out faster, while the core stillholds a lot of moisture. The same is true for concrete slabs thatare most often 4 or more inches thick.The RH method measures the moisture evaporation comingfrom the core of the concrete. This moisture evaporation will even-tually reach the surface. If too much moisture is emitted from theconcrete, the subfloor and the hardwood floor will absorb mois-ture and swell up. You may have to remove the floor, let the con-crete, the subfloor and the floor planks dry out and reinstall thefloor. Imagine all that extra work. It seems a small effort andexpense to use the RH method to check the dryness of a con-crete floor before installing the hardwood planks.

Measuring Concrete using Lignomat’s RH BluePeg

A well-designed, user-friendly system (ASTM-F2170)Once the RH BluePeg Sensors are installed and acclimated,

remove the cap, plug in the rugged, fail-proof 3.5mm connectorand read relative humidity and temperature from the DuoTec meterin your hand. Readings are immediately available, because themeter recognizes the connected sensor and indicates the valueswith the first push of the “READ” key.

After the tests are finished, the RH BluePeg Sensor can beeasily removed and re-used again.

RH BluePeg sensors can be used with the following meters:Ligno-Tec RH: only RH measurement

Ligno-DuoTec BW: RH plus pinless meter for concrete and woodLigno-VersaTec: RH plus pin and pinless meter

Relative Humidity, Temperature and EMC Chart (from the US Dept of Agriculture “Wood Handbook, Wood as an Engineering Material”)

Humidity recommendations range from 30%-50% in a building. Temperature recommendations range from 600F - 800F in a building.If you stay within the recommendation the amount of expansion and contraction is limited.

Relative HumidityTemp. 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 98

30 1.4 2.6 3.7 4.6 5.5 6.3 7.1 7.8 8.7 9.5 10.4 11.3 12.4 13.5 14.9 16.5 18.5 21.0 24.3 26.940 1.4 2.6 3.7 4.6 5.5 6.3 7.1 7.8 8.7 9.5 10.4 11.3 12.4 13.5 14.9 16.5 18.5 21.0 24.3 26.950 1.4 2.6 3.6 4.6 5.5 6.3 7.1 7.9 8.7 9.5 10.3 11.2 12.3 13.4 14.8 16.4 18.4 20.9 24.3 26.960 1.3 2.5 3.6 4.6 5.4 6.2 7.0 7.8 8.6 9.4 10.2 11.1 12.1 13.3 14.6 16.2 18.2 20.7 24.1 26.870 1.3 2.5 3.5 4.5 5.4 6.2 6.9 7.7 8.5 9.2 10.1 11.0 12.0 13.1 14.4 16.0 17.9 20.5 23.9 26.680 1.3 2.4 3.5 4.4 5.3 6.1 6.8 7.6 8.3 9.1 9.9 10.8 11.7 12.9 14.2 15.7 17.7 20.2 23.6 26.390 1.2 2.3 3.4 4.3 5.1 5.9 6.7 7.4 8.1 8.9 9.7 10.5 11.5 12.6 13.9 15.4 17.3 19.8 23.3 26.0

100 1.2 2.3 3.3 4.2 5.0 5.8 6.5 7.2 7.9 8.7 9.5 10.3 11.2 12.3 13.6 15.1 17.0 19.5 22.9 25.6

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RH BluePeg Sensor BluePeg in Sleevewith Cap

Easy-fit CableConnection to read

Lignomat USA Ltd. P.O. Box 30145 Portland, OR 97294 USA Tel: 800-227-2105 FAX: 503-255-1430 E-Mail: sales@lignomat.com www.lignomat.com