DMRB VOLUME 2 SECTION 4 PART 3 - BA 85/04 - … · concrete highway structures and those in...

May 2004

DESIGN MANUAL FOR ROADS AND BRIDGES

VOLUME 2 HIGHWAY STRUCTURES:DESIGN(SUBSTRUCTURES ANDSPECIAL STRUCTURES)MATERIALS

SECTION 4 PAINTS AND OTHERPROTECTIVE COATINGS

PART 3

BA 85/04

COATINGS FOR CONCRETE HIGHWAYSTRUCTURES AND ANCILLARYSTRUCTURES

SUMMARY

This Advice Note covers the use of coatings on newconcrete highway structures and those in service, andancillary structures such as service buildings.

INSTRUCTIONS FOR USE

This Advice Note is to be incorporated in the Manual.

1. This document supersedes BE 8/75.

2. Remove Contents pages for Volume 2, datedFebruary 2004.

3. Insert new Contents pages for Volume 2, datedMay 2004.

4. Insert BA 85/04 into Volume 2, Section 4, Part 3.

5. Please archive this sheet as appropriate.

Note: A quarterly index with a full set of VolumeContents Pages is available separately from TheStationery Office Ltd.

BA 85/04

Coatings for Concrete HighwayStructures and Ancillary Structures

Summary: This Advice Note covers the use of coatings on new concrete highwaystructures and those in service, and ancillary structures such as servicebuildings.


THE HIGHWAYS AGENCY

SCOTTISH EXECUTIVE

WELSH ASSEMBLY GOVERNMENTLLYWODRAETH CYNULLIAD CYMRU

THE DEPARTMENT FOR REGIONAL DEVELOPMENTNORTHERN IRELAND

Volume 2 Section 4Part 3 BA 85/04

May 2004

REGISTRATION OF AMENDMENTS

Amend Page No Signature & Date of Amend Page No Signature & Date ofNo incorporation of No incorporation of

amendments amendments

Registration of Amendments

VOLUME 2 HIGHWAY STRUCTURES:DESIGN(SUBSTRUCTURES ANDSPECIAL STRUCTURES)MATERIALS

SECTION 4 PAINTS AND OTHERPROTECTIVE COATINGS

PART 3

BA 85/04

COATINGS FOR CONCRETE HIGHWAYSTRUCTURES AND ANCILLARYSTRUCTURES

Contents

Chapter

1. Introduction

2. Guidance

3. References

4. Enquiries

Appendix A Surface Coatings Technology


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May 2004 1/1

Chapter 1Introduction

1. INTRODUCTION

1.1 This Advice Note supersedes BE8/75, which iswithdrawn.

Purpose and scope

1.2 The Advice Note comprises guidance on the useof surface coatings on concrete highway structures. Italso deals with coatings to be applied to the internal andexternal surfaces of ancillary structures, such as servicebuildings. Appendix A consists of a review oftechnology and practice outlining the basic principles ofcoatings technology, and describes how the constituentscan be combined to produce the wide variety of paintsand other treatments that are commonly used todecorate and protect cement-based substrates. It alsodeals with substrate characteristics that are relevant tocoating performance, and how they affect coatingselection. Finally a synopsis of the current best practiceguidance for the specification of coatings for concreteand associated substrates is given.

Implementation

1.3 This Advice Note is to be implemented forthwithfor all schemes currently being prepared provided that,in the opinion of the Overseeing Organisation, thiswould not result in significant additional expense ordelay progress. Design and Maintenance Organisationsshould confirm its application to particular schemeswith the Overseeing Organisation, and include withintechnical approval procedures and Approval inPrinciple documentation where appropriate.


Chapter 2Guidance

2. GUIDANCE

General issues and policy

2.1 Overseeing Organisations receive numerousproposals to paint or coat concrete structures. Thereasons for this are many and varied: cosmetic (as partof refurbishment and regeneration schemes on existingand new structures), decorative (murals), protective (toprovide enhanced durability or as part of measures tomitigate graffiti) and to address technical issues such asimproved light reflectance and cleaning properties inspecialist structures such as tunnels.

2.2 Previous guidance given in BE8/75 advised thatin general concrete should not be painted, primarilybecause:

• inspection may be hampered;

• structural defects may be obscured;

• additional maintenance liability may be incurred- recoating and cleaning;

• coating performance was not generally verysatisfactory;

• limited service life of paints and coatings;

• painted surfaces tended to appear dirty andshabby after a short period;

• monitoring of remedial treatments may behampered.

2.3 The philosophy behind BE8/75 is stillappropriate, and although there have been manyadvances in coating technology in the interim period,the current guidance is that in general it is not advisableto utilise coatings on external exposed concrete surfacesof highway structures. The use of paints or any otherapplied coatings for coverage of concrete surfaces onhighway structures will only be permitted inexceptional circumstances, and should be supported bytechnical justification, whole life costing andassessment of risks, based on a developed and agreedmanagement strategy for the structure. Where they arejustified and are to be adopted by agreement with theOverseeing Organisation, Appendix A of this AdviceNote provides some technical guidance to assist withthe preparation of a specification for the coatings.

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owever, where necessary, specialist technical advicehould also be sought from suppliers and manufacturersf coatings, and reference made to coating data sheets.

.4 A smooth dense concrete surface with compliantover to steel reinforcement enhances durability,ithout the need to resort to coatings, other than the

ppropriate use of a pore lining impregnant, inggressive environments where structural elements areubject to deicing salt spray or in marine environments.Surface protection using a pore lining impregnant isot specifically dealt with in this Advice Note -eference should be made to BD43 and the MCHWolume 1 Specification for Highway Works and the

elated Volume 2 Notes for Guidance). Concrete is besteft with a natural smooth defect free ‘as struck’ finishno further surface treatment after removal of thehuttering), albeit that in some situations specialoncrete surface treatment finishes may be required andan be used. Contrasts can be provided by the use ofoulding, features and textures in the concrete surface

o give areas of light and shade or by using differentggregates and cements. Further advice is available inhe ‘Appearance of Bridges and other Highwaytructures’ produced by Highways Agency andublished by HMSO.

.5 The main circumstances where coatings may beonsidered and used are as follows:

anti-graffiti coatings (as part of a managementstrategy to deal with specific graffiti problems onnew or existing structures);

(Although detailed policies on graffiti will varybetween Overseeing Organisations, generalrequirements will be to remove obscene,blasphemous or offensive graffiti as soon aspracticable after it has been observed. Howeverdiscretion is required in the handling and timingof the removal of other graffiti. Non-contentiousgraffiti should be removed, to meet set levels ofservice or intervals prescribed or agreed inparticular contracts, or in combination with otherwork where appropriate. Where graffiti ispersistent or widespread in environmentallysensitive areas, consideration should be given todifferent options, other than by frequent removalor obliteration. Possible strategies are initiativesinvolving local schools, Neighbourhood Watch,

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Chapter 2Guidance

local councils, and the Police. Physical measuresinclude the use of anti-graffiti coatings, specialcleaning materials, gritblasting, and the provisionof alternative surfaces such as tiling, and murals.Care must be taken to ensure compatibility ofapplied materials and cleaning techniques, withthe concrete substrate, and to avoid surfacedeterioration. The remedial action should notencourage further graffiti, eg Overpainting withlight coloured coatings is often seen as providinga ‘new blank canvas’. It may be appropriate insome circumstances where a coating or mural hasbeen applied to also use an anti-graffiti coating.More information is provided in ‘Appearance ofbridges and other Highway Structures’).

• anti-carbonation coatings (in association withspecific remedial treatment such aselectrochemical chloride removal, or wherecarbonation has been identified as a specific andsignificant risk);

• tunnel finishes (tunnel walls or tunnel approacheswhere light reflectance and suitability for usewith washing detergents are prime considerations- whilst the principles of coatings are dealt within this Advice Note more specific requirementsare included in the Tunnel Specification andrelated Notes for Guidance Volume 5 MCHW,BD78 and BA72);

• buried concrete surfaces;

• other inaccessible surfaces subject to potentialwater and deicing salt damage such as ends ofdecks and ballast walls;

• environmental schemes including the use ofmurals in subways or on retaining walls (othertreatments such as tiling could also beconsidered). In this case a careful study will berequired to assess the potential aesthetic andsocial benefits, as against technicalconsiderations and costs, including futuremaintenance liabilities;

• specialist applications such as anti-climb andanti-bill posting coatings.

2.6 Where coatings are considered they should beassessed in whole life cost terms as well as bydevelopment of a technical specification, to meet thedesign requirements. They should be reviewed as partof the developed management strategy for the structureconcerned.

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2.7 The guidance in this Advice Note applies both tonew construction and in-service structures. Howeverwhere consideration is being given to the application ofcoatings on in-service structures, the existing conditionof the structure must be assessed. Key issues to beaddressed are the identification of the cause of any pre-existing defects in the concrete, their method ofrectification, desired service life, costs and appearance.Coatings are only one of a number of remedial optionsavailable, either used alone or in combination withother techniques and materials.

Performance criteria

2.8 In specifying a coating for concrete, keyconsiderations will be the suitability of the proposedmaterial for application on concrete, durability, effecton the performance characteristics of the concrete,performance characteristics of the coating, appearance,maintainability, costs, application constraints, andhealth and safety issues. These topics are discussed inmore detail in Appendix A.

2.9 When specifying coatings it is essential to ensurethat the physical, chemical and electrochemicalcondition of the substrate material, and theenvironmental conditions for the coating application areappropriate. Some general guidance is given inAppendix A, however as there is a wide range ofmaterials available, used for different purposes, it isusually necessary to seek specialist advice from anexperienced materials consultant, or directly fromcoating suppliers. Where necessary detailed technicalspecifications should be consulted and research datasought. On larger schemes trials would be prudent andare strongly recommended, and also where appearanceand performance are critical. Additional testing mayalso be required to assess the performance of proposedcoatings.

2.10 Many coatings provide some form of physicalbarrier, which prevents ingress of chlorides and carbondioxide, and allows concrete to breathe, and reduces itsmoisture content. In addition to economic requirementssuch as ease of application, ease of overcoating andlong service life, the main selection criteria for coatingscan be summarised as follows:

• chemical resistance (eg to salt);

• diffusion resistance (eg to water, CO2, O2,chloride ions);

• weathering resistance (eg to UV light, variabletemperature and humidity, water);

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Chapter 2Guidance

• resistance to expansive forces (eg to freezing andthawing, alkali aggregate reaction);

• aesthetic appearance;

• crack bridging ability;

• adhesion strength;

• abrasion resistance.

Appearance

2.11 Where a coating has been agreed, considerationshould be given to the final appearance. This willdepend on the purpose of the coating, the location ofthe structure and its environment. Colour and texturemay be issues to be addressed and whether a matt orglossy finish is required. Further guidance on thesubject is available in the reference document ‘Theappearance of bridges’. Trials to assess the appearanceof the coating insitu on the structure may be required.

Anti-graffiti coatings

2.12 Unless there is a proven or anticipated problemwith vandalism and graffiti, it is still preferable to avoidthe use of coatings wherever possible. As indicated in2.5 above, and if there are no other options, anti-graffitimeasures including the use of coatings may benecessary. In selecting a suitable coating care must betaken. Appendix A section A12 indicates that somematerials, particularly permanent coatings based onurethane may alter the appearance of the concretesurface, and so should only be considered whereappearance is not critical. So called ‘sacrificialcoatings’, often wax based, are removed or partiallyremoved when cleaning and removing graffiti, andtherefore incur additional liabilities for cleaning andrenewal of the materials in the future. They generallyhave less visual impact and are preferred whereappearance matters.

2.13 Issues to be considered are the need to makespecial arrangements for the procurement of servicesfor graffiti removal and coating replacement, and thetechnical and health and safety aspects of the use ofsolvents and other cleaning materials and the need forcompatibility of materials. If extensive use of anti-graffiti coatings is to be made, and particularly whereappearance is important it is worth undertaking a trial,to assess appearance and performance of the materialwhen subject to graffiti. Combination materials mayalso become available which will address the

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requirement for pore-lining impregnants and provide ananti-graffiti capability.

2.14 In many United Kingdom locations, in areasprone to graffiti, community schemes have been set up,often involving schools and local artists to producemurals on retaining walls and subways. This has oftenbeen carried out in the design of new schemes, but hasalso been applied to in-service structures. The emphasishas usually been on the design aspects rather than thechoice of materials, but both are important. Designswhich have large blocks of colour, particularly lightcolours, may still be the target of graffiti. Persistentgraffiti may also deface good designs, unless the sourceof the problem is addressed, or unless an anti-graffiticoating is used as well. Also some paints used formurals have not proved durable and far from enhancinga neighbourhood, present a shabby appearance. Muralsdo present some difficulties in terms of maintenance ofthe mural itself, and inspection and repair of theconcrete substrate.

Anti-carbonation coatings

2.15 Anti-carbonation coatings are usually only usedin association with specialised remedial treatments suchas electrochemical chloride removal, or if concretedeterioration by carbonation is likely or has occurred.The latter is a relatively rare occurrence on highwaystructures. Some generalised guidance on anti-carbonation coatings is given at Appendix A clauseA13.

Tunnels

2.16 When selecting coatings for use within concretetunnels the key criteria is the ease of cleaning and thecolour and reflectivity to enhance the tunnel lighting.Impermeability to aggressive agents is also importantand thought should also be given to the type ofdetergents to be used for tunnel cleaning operations.Areas of the tunnel walls extending to not less than 4metres above the carriageway level shall be of aconsistent light colour and have a reflectance of not lessthan 0.6 (the method of measurement of reflectance isgiven in MCHW Volume 5). Above the light area shallbe a consistent dark colour. It is also necessary todemonstrate that the surface finish will avoid problemsof excessive specular reflection or ‘glare’ due to thereflection of daylight, vehicle lights, or illuminatedsigns. Smooth finishes are preferable, as texturedsurfaces may not be suitable as they will tend to retaindirt.

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Chapter 2Guidance

Buried concrete surfaces

2.17 Buried concrete surfaces, or faces of walls belowground, or in contact with soil or groundwater shouldreceive a waterproof coating before backfilling - referto Appendix A clause A11. Straight run bituminous andtar based compounds are generally effective, economicand durable. In the past bituminous emulsions havebeen used, but may be susceptible to failure in damp,wet or cold conditions. The acceptable materials mustbe carefully applied in accordance with themanufacturer’s recommendations, generally with aprimer and two coats, to provide a defect free surfacewithout holidays. These coatings should comply withMCHW1 Clause 2004 and be applied in accordancewith Clause 2006. Similar coatings may also berequired in inaccessible areas of bridges, which may besubject to water and other contaminants, such asbearing shelves, deck ends and ballast walls.

2.18 Where concrete is at risk of attack fromcontaminants in the ground or from sulfates, specialistadvice should be sought and reference made to BRESpecial Digest SD1 ‘Concrete in aggressive ground’.The Digest gives guidance on Protective Measures to beapplied to different mixes of concrete in varying groundconditions, including the use of waterproofing coatings.

Box sections

2.19 Generally it is not necessary to coat accessibleinterior surfaces of concrete box sections such asbeams, tanks and cellular abutments. It is moreimportant to provide a stable and benign environment,and consideration needs to be given to the provision ofadequate ventilation and drainage. If a coating isrequired then the use of a pore lining impregnant ispreferred.

Concrete in contact with water

2.20 Unless there is a specific chemical problem, thenconcrete in contact with above ground non-potablewater will generally not require the use of a coating.The emphasis should be on the use of good design anddetailing of the concrete surfaces and drainage,materials selection and good construction techniques toensure durability. Routine maintenance is alsoimportant. Where a coating is deemed necessary,specialist advice must be sought and contact made withand approval sought from the relevant responsible waterauthorities.

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ther applications

.21 There may be other specialised applicationshich require the use of a coating on concrete. Theyill need to be assessed on their merit, based on therinciples and guidance in this Advice Note. In mostses they will require detailed discussions with theanufacturer or supplier, and examination of researchidence to ensure their suitability in meeting the

erformance requirements, and in achieving the desiredurability.

ther substrates

.22 Although this Advice Note deals specifically withe application of coatings on concrete, many of the

rinciples relate to other substrates, such as masonry,rickwork and other cement based finishes. Appendix Arovides some general advice, but it is recommendedat guidance is sought from specialists or suppliers.

istoric structures

.23 Where a coating is to be used on the concreterface of a historic structure, and particularly if it is

sted or scheduled, the relevant planning and heritagethorities should be consulted, and any necessaryprovals obtained. Appearance and colour will beportant, as will be the respect to the historic fabric of

e structure, and the selection of appropriate coatingaterial and its compatibility with the substrate.

uildings

.24 This Advice Note is not intended to provideuidance in relation to the use of coatings on theternal and external surfaces of buildings, although thechnical guidance provided in Appendix A may assist the formulation of the requirements.

ompatibility with impregnants

.25 Where silane or another pore-lining impregnantas been used, and a coating is also proposed, then itould be ensured that there is compatibility betweene materials. It is particularly important to assess thate vapour transmissibility and hydrophobic properties

f the impregnant are not adversely affected orpaired, and that the performance of the coating,

articularly long term adhesion, is effective. Anyaintenance of the coating should not adversely affecte impregnant.

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Chapter 2Guidance

Specification

2.26 The use of pore lining impregnants (clause 1709)and buried concrete coatings (clauses 2004/2006) arecovered by the Specification for Highway Works andNotes for Guidance. Specification clauses for anti-graffiti coatings are in preparation, and it is intended toadd these clauses to the published Specification in duecourse. All other coatings are not covered by theSpecification for Highway Works and Notes forGuidance, and will be subject to agreement with theOverseeing Organisation, using departure procedures oras otherwise agreed.

Testing and trials

2.27 Where the use of coatings is being considered itmay be necessary to undertake performance trials toensure that the specification requirements are met. Suchtrials should be described in the specification, andspecific requirements identified.

2.28 Where manufacturer’s data sheets and testinformation are insufficient it may on occasion benecessary to subject the coating material to additionaltesting. These tests must be related to the specificationrequirements, and the tests described in thespecification.

Substrate preparation

2.29 It should be ensured that concrete surfaces towhich coatings are to be applied are dry and free fromcontamination, such as dirt, spillages, salts, leachatesand rust staining, as well as residues of curingmembranes and mould oils. Where required repairs tothe concrete should be carried out. The subsequentlyapplied coating should be compatible with the concretesubstrate and the repair materials used.

Workmanship

2.30 Details of the method and standard of applicationof coatings is generally outside the remit of this AdviceNote, but must be considered in terms of thedevelopment of the specification requirements. Wherepossible the specification should be performance based,but for some specialist materials this is impractical andit will be necessary to produce a method and materialbased specification, on a generic basis to allow as widea range of materials to be offered for selection.

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Health and safety

2.31 Some of the materials referred to in this AdviceNote and Appendix A may be injurious to health ifadequate precautions are not taken. The Appendix onlyrefers to technical suitability and performancerequirements, and in no way absolves the designer,producer, supplier or the contractor from statutoryobligations relating to health and safety at any stage inthe manufacture or use of the coatings.

2.32 A particular consideration will be the need forprotection of the substrate and other structuralcomponents, third parties, the local environment andthe workforce. Environmental considerations may alsoaffect the selection of coatings and the method ofapplication.

Records

2.33 Any structure to which a coating has beenapplied, whether new construction or in service shall beespecially noted in the as-built records and Health andSafety file. The structural elements coated shall berecorded, together with requisite details of the materialsused, manufacturer’s certificates and test data, SafetyData Sheets, source of supply, and details of any inservice requirements or restrictions, such as inspection,testing and replacement

Inspection

2.34 Concrete structural elements that have beencoated should be inspected as part of the normalstructural inspection regime (BD63/BA63). Inspectorsshould be alert to signs of deterioration in the coatingssuch as colour fading, dirt build up, graffiti, physicaldamage, chemical damage, loss of adhesion, cracking,peeling, moisture and leachates, and mould growth etc.Assessment of the continued satisfactory performanceof some coatings may require specialist tests to becarried out.

Maintenance

2.35 Concrete structural elements which have beencoated should be maintained as necessary to ensurecontinued fitness for their intended purpose. Graffitishould be removed in accordance with the prescribedservice levels. Where defects in coatings have beennoted during inspections, maintenance should beplanned and undertaken as soon as practicable, andwould normally be carried out whilst other maintenanceoperations are undertaken.

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Chapter 3References

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3. REFERENCES

Design Manual for Roads and Bridges

DMRB Volume 2 BD 43 Criteria and material for theimpregnation of concrete highway structures

DMRB Volume 2 BE 8/75 Painting of concretehighway structures

DMRB Volume 1 BD 57/BA57 Design for durability

DMRB Volume 3 BD 63/BA63 Inspection of highwaystructures

DMRB Volume 3 BA 72 Maintenance of Road Tunnels

DMRB Volume 2 BD 78 Design of road tunnels

Model Contract Document Highway Works

MCHW Volume 1 Specification for Highway Works forRoads and Bridges

MCHW Volume 2 Notes for Guidance for HighwayWorks for Roads and Bridges

MCHW Volume 5 Specification for Highway TunnelConstruction and Maintenance (Civils Works) (inpreparation)

MCHW Volume 5 Notes for Guidance on Specificationfor Highway Tunnel Construction and Maintenance(Civils Works) (in preparation)

Other references

‘Appearance of Bridges and other Highway Structures’published by HMSO

Concrete Society Report TR50 ‘Guide to surfacetreatments for protection and enhancement of concrete’

BRE Special Digest SD1 ‘Concrete in aggressiveground’


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4. ENQUIRIES

All technical enquiries or comments on this Advice Note should be sent in writing as appropriate to:

Divisional DirectorResearch & Development of Standards DivisionThe Highways AgencySunley TowersPiccadilly Plaza A JONESManchester M1 4BE Divisional Director

Chief Road EngineerScottish ExecutiveVictoria QuayEdinburgh J HOWISONEH6 6QQ Chief Road Engineer

Chief Highway EngineerTransport DirectorateWelsh Assembly GovernmentLlywodraeth Cynulliad CymruCrown Buildings J R REESCardiff Chief Highway EngineerCF10 3NQ Transport Directorate

Director of EngineeringDepartment for Regional DevelopmentRoads ServiceClarence Court10-18 Adelaide Street G W ALLISTERBelfast BT2 8GB Director of Engineering

Chapter 4Enquiries


ATINGS TECHNOLOGY

Appendix ASurface Coatings Technology

APPENDIX A: SURFACE CO

INDEX

A1. Basic principlesA2. Composition of surface coatingsA3. BindersA4. PigmentsA5. SolventsA6. AdditivesA7. Coatings for concrete and masonryA8. Substrate considerations - concreteA9. Substrate considerations - concrete blocks andconcrete bricksA10. Substrate considerations - Portland cementrenderingA11. Below ground considerationsA12. Anti-vandal treatmentsA13. Anti-carbonation coatingsA14. Performance characteristicsA15. Performance assessment of coatings: test methodsA16. Performance specificationsA17. Health and SafetyA18. References

A1. Basic principles

A1.1 Surface coatings comprise an extremely diverserange of product types designed to decorate and/orprotect substrates to which they are applied or toprovide information. They are often known genericallyas “paints”, though strictly this defines a product thatcontains colouring and opacifying materials. Clearcoatings such as varnishes, lacquers and water-repellents are also produced and can be considered tobe non-pigmented “paints”.

A1.2 A wide variety of terms are used to describecoatings products. These are often based on the use towhich they are put, examples being “car finishes”,“marine coatings” and “decorative gloss paints”,descriptors that are so wide as to be meaningless exceptin the most general of terms. Coatings are produced fortwo main sectors: the decorative/trade market and theindustrial market which, in the UK, is splitapproximately 50:50 in terms of volumes produced perannum. Industrial coatings include all those that areapplied by controlled processes or operations, usuallywithin a factory environment. Coatings used inindustrial applications are often based on exceptionallycomplex technologies, generally applied usingsophisticated equipment, and are produced for an

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extremely diverse range of substrates and end-useapplications. Coatings for the decorative/trade marketare applied on site or in-situ to buildings and otherstructures by professional painters and decoratingcontractors (trade) or by the general public (do-it-yourself). These coatings are inherently simpler incomposition, tend to be applied by traditional methodssuch as brush or roller, and are used on a morerestricted range of substrate types than their industrialcounterparts.

A2. Composition of surface coatings

A2.1 Coatings can be considered as composed of apolymeric binder (resin) which is normally dissolved ordispersed in a liquid carrier phase (solvent); a paintcoating will also contain finely dispersed particulatematerials (pigments). These basic constituents wouldform the bulk of the composition, though all coatingscontain minor additives to control and modify theproperties of the final product.

A3. Binders

A3.1 The binders used in coatings are polymericcomplexes which provide integrity to the dried film andbond it to the surface to which it is applied; binders areoften referred to as resins or polymers. A wide varietyof binders are used in the manufacture of coatings and,with some exceptions, these are all organic incomposition. Binders can be divided into two broadgroups of convertible and non-convertible types.Convertible binders are materials that are used in anunpolymerised or partially-polymerised state andwhich, following application, undergo a reaction toform a polymerised (solid) film. Non-convertiblebinders are pre-polymerised materials that are dispersedor dissolved in a carrier solvent; following application,the carrier evaporates to leave a coherent film on thesubstrate surface.

A3.2 Examples of the main types of convertible andnon-convertible binders used in surface coatings,together with an indication of their end-useapplications, are summarised in Table A1.

A3.3 Two other resinous materials are of importancein paint technology although they are not strictlyclassified as polymers, namely bitumens (USA:asphalts) and inorganic silicates.

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Table A1: Binders used in surface coatings

Binder classification and type Composition Application

Convertible

Alkyd polyester-oil complex Main binder in solvent-bornedecorative coatings

Amino eg urea-formaldehyde Industrial coatings

Epoxy diglycidyl ethers of Industrial and some specialised siteepichlorhydrin coatings

Oil eg linseed, soya or tung complex fatty acids Basis of traditional paints

Phenolic eg phenol-formaldehyde Industrial coatings

Polyurethane complex isocyanates Industrial and some specialised sitecoatings

Resins eg rosin or copal mixtures of complex acids Combined with oils to producevarnishes

Silicate ‘mineral’ binder, complex Specialised decorative coatingssilica-carbonate

Non-convertible

Acrylic eg polymethyl methacrylate Water-borne decorative coatings

Cellulose ester eg nitrocellulose Industrial coatings

Rubber eg chlorinated rubber Specialised decorative coatings

Vinyl eg polyvinyl acetate Water-borne decorative coatings

A4. Pigments

A4.1 A pigment can be defined as a solid material inthe form of small discrete particles, which remaininsoluble in the resin and solvent constituents of thecoating. Pigments are added to impart colour andopacity and/or modify the protective efficacy of thecoating on the substrate. There is a further class ofpigment which, whilst modifying the properties of thecoating by, for example, supplying water resistance,confers little or no colour or opacity; these are calledextenders. Extenders are inorganic in origin but

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pigments can be either organic or inorganic. Coatingsfor cementitious substrates may contain pigments andextenders, though the pigments are most likely to be ofthe inorganic type due to their greater durability andresistance to chemicals. A summary of the types ofpigments and extenders most commonly encountered incoatings for concrete and masonry is given in Table A2.

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Table A2: Pigments and extenders used in surface coatings

Classification Pigments Extenders

Natural inorganic Iron oxides (yellows, reds, Barytesbrowns and black) Whiting (chalk)

China clayMicaTalc

Synthetic inorganic Titanium dioxide (white) Blanc fixe (synthetic barytes)Iron oxides (yellows, reds, Paris white (synthetic whiting)browns and black)Chromium oxide (greens)Ultramarine (blues)

Natural organic None None

Synthetic organic Wide variety of yellows, oranges, Nonereds, greens, blues, and blacks

A5. Solvents

A5.1 Solvents are low viscosity liquids, oftenreferred to as volatile organic compounds (VOCs),though water is an important “solvent” in many moderncoatings and is not considered to be a VOC. Thefunction of solvents is to carry or dissolve the resincomponent, provide appropriate conditions for pigment

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Table A3: Solvents used in surface coatings

dispersion, stabilise the finished product during storage,control application characteristics and aid filmformation after application. In some coatings solventsmay be the major component of the final productthough, increasingly, coatings with low solvent contenthave been made available to users.

A5.2 The solvents most widely used in coatings areshown in Table A3.

Class of solvent Examples

Aliphatic hydrocarbons Cyclohexane, mixtures of aliphatic hydrocarbons ofspecific boiling point ranges

Aromatic hydrocarbons Toluene, xylene, styrene, mixtures of aromatichydrocarbons of specific boiling point range

Chlorinated hydrocarbons Dichloromethane, 1,1,1-trichloroethylene,trichloroethylene

Alcohols and glycols Methanol, ethanol, iospropanol, butanol, ethylene,diethylene and triethylene glycols, propylene glycols,ether derivatives of glycols

Ketones Acetone, methyl ethyl ketone, methyl isobutyl ketone,cyclohexanone

Esters Ethyl acetate, butyl acetate, esters of glycol ethers

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A6. Additives

A6.1 Many additives are used in coatings in order tocontrol or modify properties such as viscosity, flow andthe drying time of the coating, and to inhibit biologicalgrowths. These additives are generally used in lowconcentrations relative to the main formulationingredients described above. The uses of some of theimportant types of additives are summarised below.

Plasticisers: Plasticisers are organic additives that areused to increase the film flexibility of paints,particularly those based on binders that otherwisewould yield brittle films.

Driers: Driers, or drying accelerators, are oil-solublemetal salts of organic acid added to oxidation-curingsystems, such as alkyd resins, to increase the curing(drying) rate of the applied film.

Bioactive additives: Most coatings are susceptible toattack by micro-organisms such as fungi and bacteria.Apart from the obvious impairment of appearance,paint coatings may suffer degradation by micro-organisms. Bioactive additives are required to preventthis attack.

Biocides or anti-bacterial agents are incorporatedwithin water borne emulsion paints to prevent bacterial(and fungal) attack on the thickener. Biocides functionby interfering with bacterium metabolism therebypreventing enzyme synthesis, enzymes (rather than thebacteria themselves) being the active agent in paintdegradation.

Fungal growth will contribute to the degradation of apaint coating but more commonly it impairs itsappearance. In certain circumstances there may be anassociated health hazard, as in kitchens, dairies andbreweries. Fungicides are toxic agents that are includedin paint formulations to inhibit the colonisation andproliferation of fungi.

Viscosity modifiers and anti-settling agents: Paintformulations may yield liquid paints that are too fluid.With a liquid of low viscosity the flow may beexcessive for some purposes, although high flow maybe advantageous in some circumstances. Thus lowviscosity is desirable in sealers, but not in high-buildcoatings and brush-applied paints. Settlement ofpigments in storage, particularly if they are dense,occurs readily in low-viscosity paints, and heavysettlement can cause problems in redispersing thepigment. These problems of flow and pigment

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settlement can be offset by adjusting the paint viscosity.In the case of pigments, further adjustments can bemade to the formulation to counteract settlement.

Viscosity can be increased by means of thickeningagents which increase the viscosity (ie decrease flow)without introducing thixotropy.

Pigment-dispersing agents: Paint formulationsobviously require an even dispersion of pigments andextenders throughout the liquid medium. This involves,during paint manufacture, dispersion of the pigmentsand extenders in the liquid medium to break downagglomerates and uniformly wet all the particles. Forthis to occur, the medium must displace any moisture,occluded gases and fine debris on the particle surfaces;how readily this process is effected is thus of practicalimportance. While most (but not all) pigments andextenders are olephilic, that is, they are wetted bysolvent-media, only a proportion are hydrophilic orwetted by water: for example, many organic pigmentsare hydrophobic or water-repellent.

Pigment-dispersing agents, or surface-active agents, areused to facilitate pigment and extender dispersionwhere wetting by the medium is poor or even non-existent. They are often used routinely even when thereis good wetting, to ensure good dispersion.

A7. Coatings for concrete

A7.1 Whilst some cement-based surfaces areinherently weatherproof, durable and aestheticallyacceptable, others are painted for a variety of reasons;to provide colour or surface texture, to waterproofthem, to reflect or absorb light, to facilitate cleaning orfor hygiene.

A8. Substrate considerations - concrete

A8.1 Concrete is considered a durable, permanentmaterial but long-term deterioration, especially in acid-polluted air, is possible; it may, therefore, requireprotection. Following deterioration and repairs, or evenwhen new in the absence of sufficient cover to protectreinforcement, there is often a requirement to provideprotection against penetration by water, carbon dioxide,sulphur dioxide and salts. There is also an increasingneed for decorative or colouring treatments to improvethe quality of the surroundings where these containlarge areas of concrete, or even for colourlesswaterproofing treatments to prevent accumulation ofdirt and biological growths.

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A8.2 When painting concrete, the substrate surfacemay be either hard and smooth with poor adhesion forpaints (eg pre-cast components) or rough and porouswith large voids, as in mass concrete. Residues ofmould oil can seriously reduce paint adhesion; they arebest removed by abrasion rather than solvents butdetergents or emulsifying agents may be useful. Curingmembranes tend to degrade rapidly when exposed tolight but traces may persist in the pore structure ofconcrete, where they could interfere with penetration ofapplied coatings. Abrasion may be the only way ofremoving such residues, but the issue is best addressedat the specification stage where the choice of coatingsystem and curing methods are jointly considered. (Itshould be noted that abrasion should be considered as alast resort as it will damage the surface of the concreteand affect durability).

A8.3 The application of cement-based paints, or‘bagging’ with a cement/sand mix, will help to fill voidsand blowholes. Larger defects may be filled with mortaror epoxy-resin mortars, or, indoors in dry conditionsonly, with gypsum plaster or water-mixed powderfillers. Alternatively, thin-wall plasters (indoors) ortextured paints (either indoors or out) may be used tohide surface blemishes. However the acceptability ofdefects and issues of durability versus appearance mustbe assessed.

A8.4 Surface treatments can be used to reduceingress of materials to concrete that may promotecorrosion of reinforcements. For reducing ingress ofwater to concrete impervious coatings based onchlorinated rubber, two-pack epoxy resins orpolyurethanes are suitable provided the concrete isfairly dry, with a potential life of seven to 10 years tofirst maintenance. Their benefit will be more doubtfulwhere chlorides are the cause of corrosion. Coatingswhich are less impervious, to allow drying-out, but witha claimed degree of resistance to the passage of carbondioxide to minimise carbonation of concrete, have beenused with success. The technology and use of theseprotective coatings is discussed in detail in latersections of this review.

A9. Substrate considerations - concrete blocksand concrete bricks

A9.1 Dense concrete blocks and bricks may bepainted as for concrete. Some lightweight blocks allowrain penetration treatment, which may be complete (ega thick bituminous coating, with decorative coats ifneeded) or merely rain shedding and vapour permeable(eg thick textured emulsion paints).

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9.2 Aerated (and lightweight) concrete requiresaints with some filling action; emulsion paints mayuffice indoors and for purely decorative purposes, butf resistance to rain penetration is a requirement,specially in exposed situations, thick texturedelatively impervious coatings may be necessary, withhe alternative of a rendering. These will delay dryingut and should therefore only be applied when theoisture content of the aerated concrete is at a suitable

afe level.

10. Substrate considerations - Portland cementendering

10.1 The alkalinity of Portland cement is, with rarexception, so high that precautions against alkali attackf paints by new cement-based products should alwayse taken. Because of the caustic alkali present,arbonation of the lime content on ageing is not alwaysufficient to prevent the saponification of oil-paints andven when the surface pH falls to about 9, there may beurther alkali at a greater depth which will affect paintss moisture moves through. The free lime usuallyresent in cement plasters is a cause of the lime bloomhich is particularly noticeable on emulsion paints. If

arbonation is allowed to occur before painting it canreatly reduce this effect and also reduce surfaceorosity but may produce shrinkage crazing.

10.2 Cement paints are suitable for very earlyecoration; acrylic emulsion or other alkali-resistantorous paints can be used after about four weeksrying. For a glossy finish the moisture content must beown to a safe level and several months drying may beecessary. An alkali-resistant primer is needed under oilaints, hence non-saponifiable (eg chlorinated rubber)aints are preferable. Chemically-resistant wall finishesequire a hard base: cement rendering is normallyuitable if dry but if a very smooth finish is needed fornternal walls, an anhydrous plaster can be used on top.

10.3 It is often argued that the craze patterns andventual cracks which develop on painted rendering arenavoidable and not a fault of the paint. However, manyomparative tests have shown that paints differ greatlyn their ability to retard the crazing, which may appearithin one or two years under thin emulsion or masonryaints, but not for many years where the coating ishick, flexible and not highly permeable to moisture andarbon dioxide.

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A11. Below ground considerations

A11.1 Buried concrete surfaces, walls below groundand surfaces in contact with soil or groundwater shouldbe sealed on the outside before backfilling; straight runbituminous and tar based compounds are generallyeffective, economic and durable. In the past bituminousemulsions have been used, but may be susceptible tofailure in damp, wet or cold conditions. The acceptablematerials must be carefully applied in accordance withthe manufacturer’s recommendations, generally with aprimer and two coats, to provide a defect free surfacewithout holidays. These coatings should comply withMCHW1 Clause 2004 and be applied in accordancewith Clause 2006.

A11.2 Where concrete is at risk of attack fromcontaminants in the ground or from sulfates, specialistadvice should be sought and reference made to BRESpecial Digest SD1 ‘Concrete in aggressive ground’.The Digest gives guidance on Protective Measures to beapplied to different mixes of concrete in varying groundconditions, including the use of waterproofing coatings.

A12. Anti-vandal treatments

A12.1 Graffiti on untreated plain concrete surfacescan be removed by application of solvents or by high-pressure cleaning with water, but will be more difficulton textured or featured concrete. It is virtuallyimpossible to remove graffiti completely from poroussubstrates such as brick and stone, without spoilingtheir appearance. Graffiti and spills may have to bedealt with by painting over, and some manufacturerswill supply paints specially matched to the colour of thesubstrate.

A12.2 To resist graffiti, a surface which will allowremoval of most inks and paints can be produced bycoatings that form a hard and chemical-resistant film.Polyurethane coatings have been used for this purpose,and are supplied by several specialist manufacturers.Anti-vandal, or anti-graffiti, coatings generally have ahigh sheen finish; even unpigmented (clear) variantsmust be expected to cause some alteration to the naturalappearance of the substrate.

A12.3 “Sacrificial” treatments based on waxes arealso available, which tend to be less visible; whensoiled by graffiti the surface is completely cleaned offincluding some or all of the coating and the waxtreatment reapplied. Removal of large areas of graffitigenerally requires the use of specialist cleaningcontractors.

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A12.4 It is advisable to undertake trials of anti-graffiticoatings to check its effectiveness, and the effects onappearance.

A13. Anti-carbonation coatings

A13.1 Carbonation is a process whereby carbondioxide in the air penetrates the pores of the concreteand reacts with calcium hydroxide forming calciumcarbonate and water. In homogeneous concrete,carbonation proceeds inwards from the surface along afront roughly parallel to it. The rate of carbonationdepends on several factors, particularly concretepermeability (the more permeable the concrete, thefaster it will carbonate) and the relative humidityaround the concrete (carbonation occurs most rapidlywhen the relative humidity is around 55-75%).

A13.2 To minimise the risk of subsequentdeterioration, a coating may be applied over the wholeexterior surface of the concrete to reduce the rate ofcarbonation by acting as a barrier to the penetration ofcarbon dioxide. It should also prevent ingress of liquidwater, but allow water vapour to pass through it. Thiswill prevent entrapment of liquid water in the concreteand between the coating and substrate. The coatingtreatment must, of course, be suitable for application toconcrete. Furthermore, for coatings to serve as a barrierto carbon dioxide they must form a defect-free film.The surface of concrete is irregular and uneven;blowholes and other surface imperfections are quitecommon, so multiple coats reduce the risk of coincidentdefects.

A14. Performance characteristics

Basic principles

A14.1 The durability of a paint system is its ability toprovide decoration and/or protection to its substrateover the period of time known as its effective servicelife. This period is the interval between the time ofapplication of the paint system and the moment atwhich, through deterioration, it ceases to perform itsrequired function. The durability of paint films isdependent upon a number of factors. These can bedivided into ‘internal’ factors, such as formulationdetails and their effects on the physio-chemicalcharacteristics of the coating, and ‘external’ factorssuch as the nature of the substrate, substratepreparation, location effects and weather. The latter twofactors and their influence on paint durability will beconsidered in this section, the other factors havingalready been discussed in other sections of this report.

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A14.2 The environmental conditions to which paintfilms are exposed during service are of greatimportance in determining their performance.Knowledge of the anticipated service conditions isessential when formulating or specifying paint coatings.Environmental factors can be subdivided into theeffects of location, that is, atmospheric pollution, andthe effects of weather.

Influence of location on durability

A14.3 The prevailing atmospheric conditions to whicha paint film is subject can be categorised into fourgroups, namely, very severe, severe, moderate and mild.

A14.4 Very severe and severe exposure conditions areexperienced in coastal situations, within industrialregions, near to areas of heavy industrial pollution andwhere complete immersion in water or chemicals mayoccur. Paint systems required to withstand severeexposure have to possess the highest durability.Typically, this necessitates the use of paints based onchemical resistant binders such as the epoxide,polyurethane, vinyl or chlorinated rubber resins, andthese materials are used in situations where limitedaccess makes maintenance difficult or when costconsiderations dictate a long maintenance-free servicelife. However, often conventional alkyd type paints areused, of necessity, in such severe exposure conditions.The durability of these alkyd paints is not normallyconsidered to be of the highest order but improvedperformance and an initial high degree of protection isconferred on the substrate by the provision of extra filmthickness. This is most conveniently achieved by theapplication of two, rather than one, finishing coats overthe undercoat and primer coats. In general however,their use under such conditions should not beencouraged.

A14.5 Moderate exposure conditions are experiencedin light industrial and urban regions away from heavyindustrial conurbations and coastal areas. Mildconditions are found in sheltered exterior areas awayfrom pollution, and in most interior situations.

A14.6 Paint systems for the moderate and mildexposure conditions are, typically, based on alkyds,oleoresinous varnishes and emulsion resin binders.However, it is not uncommon for a paint system to berequired to exhibit a greater durability than suggestedby its immediate environment. Typically, interior paintswhich need to withstand abrasion or frequent washingdown fall into this category, and here high durabilitypaints would have to be specified. The ability of paint

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lms to withstand location effects is primarilyependent upon their chemical resistance, aaracteristic dictated by the nature of the ingredients

sed in the formulation.

14.7 Most types of coating systems are resistant toe dilute acidic environments which can occur inrtain exposure conditions, for example, an industrial

r urban conurbation where sulphur-containing fossilels are burned. However, the presence of sulphur

xides in the atmosphere can cause increased dryingmes and premature loss of gloss in recently applied airrying, oxidative systems, although, in general, thesefects do not reduce the effectiveness of coating

erformance.

14.8 The formulation of paints, in particular thoseased on oleoresinous varnishes and alkyds, aresceptible to attack in dilute alkaline conditions.here alkali resistance is required, alternative resinpes such as the polyurethane, chlorinated rubber and

inyl copolymers have to be used. In situations wherer drying oxidative formulations are required, alkydsodified with these more resistant resins can be used to

roduce resistant paint systems. Resistance toncentrated alkalis, however, is more difficult tohieve since this medium tends to attack all coatingpes, particularly on prolonged immersion.

14.9 Coatings resistant to oils and organic solventse also required in certain service situations and, as a

eneralisation, coatings with a complex cross-linkedructure provide the highest resistance. Paint films canffer severe attack from solvents, especially thelorinated hydrocarbons (which are the basis of many

aint strippers), ketones, esters and the aromaticydrocarbons. Non-convertible coatings rarely provideood resistance to solvents.

14.10 The pigmentation of paints can also beversely affected by pollutants, in particular, acids andkalis. Oils and solvents generally have little chemicalfect on pigments, although with certain organic

igments the phenomenon known as ‘bleeding’ canccur on overcoating. This effect is caused by solvents the freshly applied coating solubilising the

igmentation in the underlying film. This solubilisedigment can be carried through the freshly applied film it dries, usually resulting in a patchy surface

iscolouration. The phenomenon of ‘bleeding’ ispecially prevalent where aromatic hydrocarbon, esterd ketone types of solvents are present in the paintrmulation.

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Influence of weather on durability

A14.11 The effects of weather on paint films is oftenmarked and can lead to rapid degradation of coatingsystems. All of the components of weather -temperature, moisture and radiation (sunlight) - caninfluence paint film performance and, clearly, sinceweather is a complex of these components, interactionscan occur which render particular combinations severeand others relatively mild.

Resistance to ultra-violet radiation

A14.12 Prolonged exposure of many types of paintfilms to sunlight results in their rapid degradation, andthis is primarily attributable to the ultra-violetwavelengths. Ultra-violet degradation of paint films is acomplex process involving both an increase in thecross-link density of the internal molecular structure ofthe film binder and, concomitantly, a tendency forcertain constituent structural bonds to rupture. Theresult of this process is that the film becomes toughduring the early stages of exposure. Eventually,however, the film becomes brittle, cracks, andultimately, as water permeates through the film, it losesadhesion and delaminates (flakes) from the substrate.To offset this process, it is common practice to addpigmentary materials having the ability to absorb ultra-violet radiation to paints designed for exterior exposure.Titanium dioxide is an example of such a pigment and itfunctions by both absorbing the ultra-violet light andreflecting it away from the film, thus protecting thepolymer. Invariably with this pigment, back-scatterfrom pigment particles in lower levels of the filmresults in a certain amount of polymer degradation andthis process releases small amounts of the pigment fromthe matrix. This reaction, known as ‘chalking’, isexhibited to varying degrees by all types of titaniumdioxide but it can be used to provide a degree of self-cleansing within coatings. It is, of course, detrimental tothe performance of coloured paints containing titaniumsince the colour of the film could alter markedly withprolonged exposure. However, by careful selection ofpigments, this chalking process can be reduced to aminimum so that, for example, colour changesattributable to this mechanism will not be detectable fora period of several years.

A14.13 Selection of the binder type is also important indetermining the susceptibility of the paint film to ultra-violet light degradation. Polymers containing aromaticring structures are particularly susceptible to ultra-violet degradation since they strongly absorb in theultra-violet wavelength region of sunlight, that is 290-

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350 mm. Binders without these structures are inherentlymore durable although in many instances, otherperformance aspects may render them unsuitable foruse in exterior situations.

Resistance to moisture

A14.14 Moisture also adversely affects paint filmdurability, particularly when it is present in the form ofrain or condensation. Consideration must also be givento moisture levels within concrete and the location andeffectiveness of structural drainage systems. Thepresence of moisture on a substrate during paintapplication is, generally, detrimental to paint durabilitysince it will usually reduce the adhesion of the coatingsystem. This effect is particularly marked on ferrousmetal substrates, where underfilm corrosion processescan be initiated. With porous substrates such asconcrete and other cement-based materials, surfacemoisture, unless present in excess, is generally notdetrimental to durability.

A14.15 Condensation of atmospheric water vapour orrainfall onto the surface of freshly applied paints caneffect a premature loss of gloss in all types of coatingsystem due to disruption of the surface. Normallyhowever, this would not result in any long termreduction in paint durability.

A14.16 Painting in conditions of high atmospherichumidity, that is greater than 90%, generally increasesthe drying times of air drying oxidative paint systems.However, the drying process is not entirely suppressedand provided that the film is not damaged mechanicallyor by prolonged precipitation of rain, snow, frost, etc.whilst in the wet condition, then subsequent durabilityis not likely to be affected.

Temperature effects

A14.17 The combination of low temperature and highhumidity can also present drying problems, especiallywithin the aqueous emulsion paint systems where filmformation is due to evaporation of the aqueous phaseand coalescence of the resin particles. With manyemulsion systems, optimum coalescence will not occurat temperatures below about 5°C and since the filmformed is not in a coherent state and will notsubsequently become so, then the durability will beabnormally low.

A14.18 Low ambient temperatures can also adverselyaffect the curing rate of many types of two pack epoxy-and polyurethane-based paint systems and certain of

May 2004



these coating types will not form films at temperaturesbelow 10°C without the use of additional catalysts.Non-convertible coatings, that is those that dry bysolvent evaporation such as those based on chlorinatedrubber and vinyl resins, will dry at very lowtemperatures and, as such, are ideally suited for winteruse. However, the drying times of these types ofcoatings will be increased at any temperatures instagnant air conditions, since under thesecircumstances, the solvent released by the coating willtend to blanket the surface and impede the evaporationprocesses.

A14.19 Tropical and high heat/high humidityconditions can also adversely affect the durability ofpaint coatings. Exposure to high air temperatures, thatis, 50°C or above, can result in a rapid embrittlement ofpaint films. In convertible systems, this would be due toan acceleration in the cross-linking rate, whereas withnon-converting coatings, this could be due to a loss ofplasticiser or residual solvent from the film.

May 2004

Furthermore, the expansion and contraction resultingfrom the temperature cycling of the substrate caninduce cracking within brittle paint systems.

A14.20 High atmospheric temperature effects can bereduced by the use of white pigmentation. Typically,surface film temperature of paints with a whitepigmentation are half those with a black pigmentationunder conditions of summer exposure.

A15. Performance assessment of coatings : testmethods

Introduction

A15.1 Standard test methods exist for most of theimportant properties required by coatings for concreteand masonry, and are detailed in European Standards,Table A4.

Table A4: European Standard identification tests for surface treatment of concrete

Test method CEN test numbers

Specific weight prEN 1880-1prEN 1880-2

Infrared spectrum prEN 1767

Determination of epoxy equivalent prEN 1877-1

Determination of amine products prEN 1877-2

Determination of hydroxyl value -

Determination of isocyanate content -

Determination of volatile and non-volatile matter prEN 1768

Determination of ash by direct calcination prEN 1879

Thermogravimetric analysis prEN 1878

Determination of flow time by use of flow cups -

Determination of viscosity EN ISO 3219

Surface drying - Ballotini method prEN 1769

Determination of pot life as a function of temperature EN ISO 9514

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A16. Performance specifications

Introduction

A16.1 It is evident from the previous section thatEuropean Standards will have a profound impact on thecoatings industry and its clients. There will be standardrequirements for surface treatments applied to concreteand, for the first time, coatings used by public bodieswill be able to be specified by CEN standards, and CEmarking will be used by manufacturers.

CE marking

A16.2 Once the relevant European Standards arepublished, masonry coatings that are CE marked will bemade available by manufacturers. The CE mark willdemonstrate that the coating conforms to Communitylegislation in respect of compliance with the essentialrequirements of the Construction Products Directive,however it is not a quality mark as such. Manymanufacturers will undoubtedly undertake productcertification to provide extra assurance to users, and itis a requirement that any such labelling must be affixedin such a way that it can be distinguished clearly fromthe CE mark.

A16.3 The general principles for specification ofcoatings for concrete and masonry are summarised inthe following sections.

General principles of coating specification

A16.4 The general principles of best practice incoating specification for concrete and masonry coatingscan be summarised as:

• the substrate must be suitably sound and properlyprepared;

• the appropriate coating system must be specified;

• the coating must be applied followingmanufacturers’ recommendations;

• the coating must be applied under suitableweather conditions;

• the coating must be maintained at regularintervals.

A16.5 These general principles of specification willvary in detail depending on whether the surfaces to bepainted are fresh or aged/weathered.

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New surfaces

A16.6 The performance of coatings applied to newcement-containing substrates, such as concrete, can beinfluenced by the type of mix, type of admixture, timeof cure before painting, ambient conditions and type ofsurface preparation.

A16.7 Assuming that the quality of the concrete isgood, and that it is not excessively porous, then themost important factor is the surface preparation carriedout before coating. All dirt, grease, and othercontaminants must be removed, and there should be nosurface laitance. Surface defects such as blow holesshould be made good by filling with a purpose-designedfiller. The most important factor determining coatingselection then are the service conditions to which thecoating will be exposed (see later).

A16.8 The other factors will all influence coatingselection and performance to some extent, assummarised below:

• The type of mix is likely to be of littleimportance.

• The type of admixture may have an effect,especially waterproofing additives, which mightadversely affect the adhesion of coatings.

• As with any surface to be coated, the ambientconditions may influence coating selection, andwill certainly affect coating application. Forexample, water-borne coatings are moreproblematic in adverse weather conditions thanequivalent but solvent-borne variants.

• Concrete can be successfully coated once it hasreached a minimum of 80 per cent of the designstrength.

• Saponifiable coatings, such as those based on oil-containing binder systems, should not be used onnew cement-containing substrates, unless thealkalinity is low and the substrate unlikely tobecome wetted in service.

• Coatings of low permeability should not be usedon new substrates of high moisture contentbecause of the risk of blistering. Manufacturers’recommendations must be followed.

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Aged/weathered surfaces

A16.9 The most important consideration whenpainting aged, and especially weathered surfaces, is thecondition of the surface, as summarised below:

• Surfaces must be thoroughly cleaned to be free ofall loose material.

• Moulds, lichens or algal growths must beremoved, and the affected areas treated with anapproved masonry biocide.

• Graffiti, or other contaminants, which may affectapplied coatings, must be removed or effectivelysealed in. Specialist advice may be required.

• Defects such as hollow rendering, large cracks,failed pointing, should be made good using anappropriate filler or mortar mix.

• Efflorescence should be brushed off and thesource of dampness identified and rectified. Nocoating will resist efflorescence.

• Coatings should be specified in accordance withthe substrate, especially its moisture content,alkalinity and general condition as noted above.Manufacturers’ recommendations must befollowed.

Coating specification

A16.10 A key factor in deciding on a coatingspecification is the service environment to which thecoating will be exposed. British Standard BS 6150identifies four categories of climate; Mild, Moderate,Severe, Very severe, with implications for coatingselection.

Classification of climatic factors

A16.11 The four climatic categories identified inBS 6150 can be experienced under both interior andexterior exposure conditions, but it is assumed here thatthe primary interest for the Overseeing Organisations isthe exterior situation. General descriptions of the fourcategories of climate are given below, together withbroad indications of the effect of the climatic conditionson coating specification for exterior concrete andmasonry.

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Mild: Inland areas (more than 10 km from the coast),non-industrial, and with average rainfall. All types ofcoatings will afford satisfactory service.

Moderate: Semi-coastal areas (3 km to 10 km inland),non-industrial, with average rainfall. Inland areas (morethan 10 km from the coast), urban or light industrial,with mild atmospheric pollution, but not in closeproximity to the source of pollution. Most coatings ofconventional type are likely to afford satisfactoryservice.

Severe: Coastal areas subject to salt spray (up to 3 kminland), non-industrial, with average rainfall. Inlandindustrial areas with significant atmospheric pollution.Areas with high levels of rainfall. Conventionalcoatings can be used but will have significantly shorterservice life than in Moderate conditions. The use ofspecialist coatings may be required if long serviceintervals without maintenance are required.

Very severe: Coastal or industrial areas with significantatmospheric pollution. Specialist coatings will berequired, supported by expert advice from themanufacturers.

Specification of coatings for exterior cement-basedsubstrates

A16.12 As outlined in the previous sections thedevelopment of coatings specifications is dependant ona number of important factors. This complexity makesestablishing generic specifications that are applicable toall circumstances of use extremely difficult. Generalguidance is possible however, and coating selection in asystematic manner depending on the substrate condition(in respect of moisture content) based on best practiceguidance given in BS 6150.

A16.13 Assuming that a substrate is sound, and as themoisture regime in the substrate increases, then theoptions for coating selection reduce, as indeed must theexpected time to first maintenance. There are alsoclearly benefits in ensuring that the substrate is “dry” atthe time of coating, since this condition provides thewidest range of coating options, some of which havethe potential for providing maintenance intervals of10 years or more.

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Specification of impregnation treatments forcement-based substrates

A16.14 The coatings described so far in this reviewhave been film-forming, that is intended to deposit onthe surface a layer of appreciable and measurablethickness. There are some products however, that whilstclassed as “coatings” protect by absorption into theoutermost layer of the substrate where they confer someextra property; strictly these are impregnationtreatments rather than coatings, and are dealt with inBD43 and the Specification for Highway Works andrelated Notes for Guidance clause 1709.

Specification of anti-vandal treatments

A16.15 Consideration of the need for anti-vandaltreatments normally arises after an attack has occurred.Special cleaning products are available that are claimedto be effective at removing graffiti from unprotectedconcrete and masonry surfaces, the cleaning productsbeing purpose designed to suit the porosity of thesubstrate. Once cleaned, an enhanced level ofprotection against further spoilage can then be obtainedby application of an anti-vandal treatment.

A16.16 Two main types of treatment are used forprotection against graffiti, the so-called “permanent”treatments and the “sacrificial” treatments. Permanenttreatments seal the surface and form a coherent coatingthat is not readily penetrated by graffiti in the form ofpaint or ink. The graffiti can therefore be removed withcleaning agents leaving the protective coating intact;depending on the type and severity of the graffiti a twostage approach to removal may be required, comprisinginitial cleaning with solvents or detergents and then useof poultices to remove any residual staining within thecoating. Sacrificial products are designed to be easilyremoved by washing taking any graffiti away in theprocess. Protection must then be restored by applicationof fresh coating material.

A16.17 Both types of anti-graffiti treatments arenormally supplied in an unpigmented (clear) formthereby leaving the appearance of the surface largelyunaffected. The service life of anti-vandal treatmentswill depend on the exact composition, but sometreatments are claimed to remain resistant to vandalismfor up to 10 years without re-treatment.

A16.18 Application of anti-vandal coatings generallyrequires no special skills and can be undertaken byprofessional painters. However, removal of graffiti,especially from large areas, often requires use of

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aggressive chemicals and processes and is bestundertaken by specialist contractors.

A16.19 Many suppliers of anti-vandal treatments canoffer detailed advice on specification based onexperience developed over many years. This area ofcoatings technology is extremely specialised, andthough the general advice given here outlines the basicprinciples of specification and use of anti-vandaltreatments, detailed recommendations should be soughtfrom manufacturers if use of such products is beingconsidered.

A17. Health and Safety

A17.1 When specifying coatings consideration shouldbe given to the implications of the relevant Health andSafety legislation. Particular attention is drawn tocompliance with the Control of Substances Hazardousto Health (COSHH) requirements, and the need toensure the Health and Safety of operatives, other sitestaff and third parties such as motorists, and adjacentanimal and plant life. This may entail the use ofphysical protection and barriers, to ensure adequateprotection, as well as controlled environmentalconditions during coating application. Where work isproceeding in the vicinity of live traffic, special trafficmanagement measures may be necessary. Workadjacent to railway lines or water courses requires priorconsultation with the responsible authorities andinclusion of any special requirements in Contractdocuments to facilitate safe practices.

A18. References

National, European and International Standards

BS 3900 Part G6 - Methods of Test for Paints:Assessment of Resistance to Fungal Growth

BS 6150 - Code of Practice for Painting of Buildings

DIN 52617 - Determination of Water AbsorptionCoefficient of Construction Materials

prEN 1062 - Paints and Varnishes: Coating Materialsand Coating Systems for Exterior Masonry

EN 1062-1 - Classification for Masonry CoatingsprEN 1062-2 - Determination and Classificationof Water Vapour Transmission RateprEN 1062-3 - Determination and Classificationof Liquid Water Transmission RateParts 4, 5, 6,7.8.9,11 - in development

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prEN 1504 - Products and Systems for the Protectionand Repair of Concrete Structures

prEN 1504-2 Classification System for SurfaceTreatment of ConcreteENV 1504-9 - Guidance Note on the Principlesof Repair of ConcreteprEN 1504-10 - Site Application of Products andSystems and Quality Control of the Works

prEN 1542 - Products and Systems for the Protectionand Repair of Concrete Structures - Test Methods: ThePull-off Test

prEN 1767- Products and Systems for the Protectionand Repair of Concrete Structures - Test Methods:Infrared Analysis

prEN 1768 - Products and Systems for the Protectionand Repair of Concrete Structures - Test Methods:Determination of Volatile and Non-volatile Matter

prEN 1769 - Products and Systems for the Protectionand Repair of Concrete Structures - Test Methods;Surface Drying Test - Ballotini Method

prEN 1877 - Products and Systems for the Protectionand Repair of Concrete Structures - Test Methods;Reactive Function Relating to Epoxy Resins

prEN 1877-1 Determination of Epoxy EquivalentprEN 1877-2 Determination of Amine FunctionUsing the Total Basicity Number

prEN 1878 - Products and Systems for the Protectionand Repair of Concrete Structures - Test Methods;Reactive Function Relating to Epoxy Resins;Thermogravimetry of polymers - Temperature ScanningMethod

prEN 1879 - Products and Systems for the Protectionand Repair of Concrete Structures - Test Methods;Determination of Ash by Direct Calcination

prEN 1880 - Products and Systems for the Protectionand Repair of Concrete Structures

prEN 1880-1 - Test Methods: Specific Weight -The Pkyometer MethodprEN 1880-2 - Test Methods: Specific Weight -Immersed Body Method

EN ISO 2812-1 - Paints and Varnishes - Determinationof Resistance to Liquids - Part 1: General Methods

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RR“R1

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May 2004

N ISO 3219 - Plastics: Polymers/Resins in Liquidtate as Emulsions or Dispersions - Determination ofiscosity Using a Rotational Viscometer with Definedhear Rate

N ISO 6772 - Paints and Varnishes Falling-Weightest

N ISO 9514 - Paints and Varnishes - Determination ofhe Pot Life of Liquid Systems - Preparation andonditioning of Samples and Guidelines for Testing

SO 7783-1 - Paints and Varnishes - Determination ofater Vapour Transmission Rate - Part 1: Dish Method

or Free Films

N 196-1 - Method of Testing Cement: Determinationf Strength

N 24624 - Paints and Varnishes: Pull-off Test fordhesion

SO 11507 - Paints and Varnishes - Exposure ofoatings to Artificial Weathering - Exposure toluorescent UV and Water

SO 11998 - Paints and Varnishes - Determination ofet Scrub Resistance and Cleanability of Coatings

RE publications

.H. Roberts, Building Research Establishment,nformation Paper IP 21/86, “Determination of thehloride and Cement Contents of Hardened Concrete”,ecember 1986.

.W.J. Treadaway and H. Davies, Building Researchstablishment, Information Paper IP 14/88, “Corrosion-rotected and Corrosion-Resistant Reinforcement inoncrete”, November 1988.

. Davies and G.W. Rothwell, Building Researchstablishment, Information Paper IP 7/89, “Theffectiveness of Surface Coatings in Reducingarbonation of Reinforced Concrete”, May 1989.

.N. Cox, A.T. Coote, and H. Davies, Buildingesearch Establishment, Information Paper IP 18/89,Results of Exposure Tests to Evaluate Repairs toeinforced Concrete in Marine Conditions”, November989.

uilding Research Establishment, BRE Digest 197,Painting Walls, Part 1: Choice of Paint”, 1977.

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Building Research Establishment, BRE Digest 263,“The Durability of Steel in Concrete, Part 1:Mechanism of Protection and Corrosion”, 1982.

Building Research Establishment, BRE Digest 264,“The Durability of Steel in Concrete, Part 2: Diagnosisand Assessment of Corrosion-Cracked Concrete”, 1982.

Building Research Establishment, BRE Digest 280,“Cleaning External Surfaces of Buildings”, 1983.

Building Research Establishment, BRE Digest 325,“Concrete, Part 1: Materials”, 1987.

Building Research Establishment, BRE Digest 326,“Concrete, Part 2: Specification, Materials, and QualityControl”, 1987.

Building Research Establishment, BRE Digest 330,“Alkali Aggregate Reactions in Concrete”, 1988.

Building Research Establishment, BRE Digest 397,“Standardisation in support of European legislation:what does it mean for the UK construction industry”,1995.

Building Research Establishment, BRE Digest 405,“Carbonation of Concrete and its Effects onDurability”, 1995.

Building Research Establishment, BRE Digest 408, “Aguide to attestation of conformity under theConstruction Products Directive”, 1995.

May 2004A/14

DMRB VOLUME 2 SECTION 4 PART 3 - BA 85/04 - … · concrete highway structures and those in...

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