CONFERENCE PAPER NO. 60 (1998) Durability Aspects for Coatings on Buildings in Australia and New Zealand. Adrian F. Bennett

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1 CONFERENCE PAPER NO. 60 (1998) Durability Aspects for Coatings on Buildings in Australia and New Zealand Adrian F. Bennett Presented at the IUFRO Working Party Conference, Rotorua, November 30 - December 2, 1998 ISSN:

2 DURABILITY ASPECTS FOR COATINGS ON BUILDINGS IN AUSTRALIA AND NEW ZEALAND Adrian Bennett, Materials Manager - BRANZ Introduction The performance and durability of coatings is a topic that keeps providers of building research, advice and consultancy services busy. A large part of this work is generated by the failure of coatings to perform up to the expectation of the user. There are a wide variety of reasons why coatings fail including the following: 1. Substrate selection and preparation 2. Application/application conditions 3. Incorrect coating selection 4. Inadequate or unexpected coating performance 5. Expected service life already exceeded 6. Incorrect or inadequate maintenance Items 1-3 above are problems that the coatings industry is well aware of and spends a considerable amount of effort in attempting to educate users about and in troubleshooting problems. While important they are not the main topic of this paper. The last three items above are of interest for this - Quality Assurance for Exterior Wood Coatings workshop. This paper reviews the expectations of the consumer and manufacturer, relevant codes and standards and industry experiences with coatings. It concludes with a case for the continued development of standards that allow for an improved understanding and demonstration of acceptable coating performance. Industry Expectations Building Owners/Specifiers When choosing a coating system, building designers/owners have a number of expectations. The need to meet any relevant New Zealand Building Code (NZBC) requirement is an obvious starting point and is covered in the next section of this paper. Consumers will often have an expectation of coating performance (particularly aesthetics) that exceeds any building code requirements. This will have been built up from their own experience of general coating performance and may or may not be realistic for different coating types and applications. There are also many occasions where coatings do not have any specific building code requirements, they will still want an assurance of satisfactory performance. This can readily be demonstrated with coating systems that have a reasonable history of use in the market. However, even with products that have been on the market for many years, formulation changes are common. These may be in response to changes in the supply of raw materials or to take advantage of improvements in paint technology. Minor changes may not have any effect on coating performance, but major reformulations may necessitate substantial re-testing. With new products, the basic consumer may rely on the Brand Name or the advice of a retail assistant to gain confidence in a product, or

3 simply buy on price. More educated buyers will be looking for evidence of performance or a solid warranty from the supplier. A key long term performance issue for the consumer and specifier is knowledge of maintenance requirements. In many cases the consumer may be unaware or poorly informed of the recommended maintenance required for the coating system to reach or even exceed its design life. This can lead to dissatisfaction with the product and involve all parties in costly dispute procedures. If specifiers do not obtain and pass this information on, then the client is likely to hold them liable for poor performance. Coating Manufacturers/Suppliers Since the basic function of any supplier is to provide products which meet their customers needs, the customers requirements are also the supplier s requirements. In addition, reputable suppliers are looking to differentiate their products in the marketplace from those that are considered poor performers. Failures of their own products or inferior competing products will also result in negative publicity for the whole coating industry. To assist in product differentiation, manufacturers may offer substantial performance warranties on their products. To do this with confidence, they need to have a good understanding of the properties and performance of their coating systems and ensure that this is communicated to customers. This requires that a comprehensive testing programme is put in place, which provides a realistic evaluation of the properties and performance of the coating system in the anticipated application and service conditions. This is where the development and use of suitable codes and standards can play a major role in ensuring that both manufacturers, suppliers and users can be confident in the performance of coatings. Codes and Standards The New Zealand Building Code (NZBC) The NZBC (BIA, 1992) defines the expected performance of buildings in New Zealand. The NZBC is performance-based and as such, does not prescribe how buildings must be built. It is primarily driven by health and safety considerations and aesthetic concerns are not considered. Coatings are not considered as an individual item in the NZBC, but when used as part of a system these may have to meet various Code requirements. The NZBC consists of 35 clauses covering a range of building functions. Those that have some specific relevance to coatings are listed below: B1 Structure B2 Durability C2 Means of escape (during fire) C3 Spread of fire C4 Structural stability during fire E2 External Moisture E3 Internal moisture G3 Food preparation and prevention of contamination The durability clause is somewhat different from the other clauses in that its purpose is to ensure that building elements meet the requirements of other relevant NZBC

4 clauses for the life of the building. Specifically, coatings will have a durability requirement only where they are needed to ensure that the underlying material will perform its intended function for the required time. What this means is that items that are not required by the NZBC (eg. decorative items) have no durability requirement. This is of particular relevance to coatings which, in many cases, are used for decorative purposes although they will at the same time contribute to enhanced durability of the underlying materials. Examples of situations where coatings have a durability requirement are: coatings on non-durable exterior claddings (such as untreated and H1 treated radiata pine, galvanized steel in certain locations) coatings which are required for waterproofing claddings or wet areas coatings required for food preparation areas coatings required for fire protection. The actual durability required under NZBC B2 for coatings will depend on the specific application. In cases where access and replacement are easy, a 5-year durability is specified. In cases where access or replacement are more difficult a 15- year durability is required. There may some cases where the circumstances surrounding the use of a coating necessitate a 50-year durability. An example would be the use of tanking membranes which are buried below ground and are completely inaccessible. The durability requirements allow for normal maintenance during the required service life. This specifically excludes total replacement, but would allow for things such as washing down and minor touch ups. Where a coating is used on a nondurable timber cladding, the coating has a 5-year durability requirement, but the coated timber must perform for at least 15 years. Normal maintenance of the coated timber could include repainting at a nominated period (possibly 5 years, but more typically 8-10 years) within the 15-year interval. Showing Compliance with the NZBC Performance-based codes usually include prescriptive documents or methods of calculation or test which, when followed, demonstrate compliance with the performance requirements. In New Zealand these are called Approved Documents and include both Verification Methods (means of demonstrating compliance) and Acceptable Solutions (prescriptive methods of compliance). These are often inherited from previous building regulations, may have been developed as New Zealand Standards (NZS) or are documents prepared specifically for this purpose. There are no Approved Documents that deal specifically with the durability of coatings over timber or other cladding materials. The Acceptable Solutions for Fire clauses C3 does cover specific coating requirements for spread of flame, smoke etc and provides a means of testing for these via Australian Standard AS 1530 part 3. Coatings are referenced indirectly in some of the other Acceptable Solutions, eg. NZBC B2 Durability B2/AS1 references NZS 3602 for selecting timber for use in light timber frame construction. In this document, a three-coat paint system is specified for non durable cladding timbers or timber with non-fixed preservative

5 treatment. However, there are no performance specifications that the coating must meet to be deemed suitable for this use. One of the shortcomings in the current NZBC B2 is the scarcity of information on selecting durable materials or on how to test specific materials for durability. This is not due to an unwillingness on the part of the code writers, but reflects the difficulty in providing comprehensive guidance on the wide range of materials, environments and potential uses of building materials. There is an opportunity for groups with specific interests to develop test methods, which can become the basis for future Acceptable Solutions. Building Code of Australia (BCA) For convenience, the BCA (Australian Building Codes Board, 1996) has separate volumes for housing and associated buildings such as sheds and carports (Class 1 and 10 buildings), and commercial/institutional structures (Classes 2-9). The BCA has no specific performance requirements for coatings, however, compliance with the some of the Performance Provisions may involve the use of coatings. For example, with class 1 & 10 buildings, satisfying the following Performance Provisions; 2.2 Damp and weatherproofing, 2.3 Fire safety and 2.4 Health and amenity, could involve the use of coatings. For Class 2-9 buildings, the same issues are covered under C:Fire and F:Health and amenity. Deemed-to-satisfy documents do contain direct references to coatings, eg. Volume II Part Weatherproofing of Masonry, lists three coats of acrylic based exterior gloss paint as an acceptable weatherproofing for single skin masonry. There is no separate durability provision specifying time periods for the service life of building elements in the BCA (in contrast to the NZBC) or how to assess durability. The BCA does however, contain clauses in both Volume I (A2.1 and A2.2) and Volume II (1.2.1 and 1.2.2) which specify that materials must be fit for the purpose they are intended for, and listing the evidence acceptable to show suitability. The latter includes: reports from registered testing authorities certificates of conformity or accreditation a certificate from an appropriately qualified person an appraisal certificate other documentary evidence. As previously noted for the NZBC, there is the opportunity for suitable standards to become useful tools for showing compliance with the BCA. New Zealand and Australian Standards Standards New Zealand develops standards across a wide range of areas including construction. As noted above, some may be developed specifically for use in an Approved Document, others as industry good practice guides, while others may end up by becoming mandatory documents under government legislation. In recent years New Zealand has formed closer a relationship in the standards area with Australia. This has lead to the adoption of many Australian Standards as joint Australian/New Zealand Standards. A further trend which has emerged is the move to adopt

6 International Standards (ISO) as Australian/New Zealand standards. Developments in European and International (ISO) Standards are discussed in other papers presented at this workshop. The main standard in New Zealand relating to painting of buildings is NZS This was published in 1985 and is likely to be replaced by AS 2311 (as AS/NZS 2311), which is currently being revised. AS/NZS 2311 provides a lot of helpful information on many aspects of painting, including substrate preparation and paint selection. It includes tables setting out commonly acceptable paint systems for a variety of building elements. It also contains general information on factors affecting the performance of coatings. It does not however, set out how the durability of a coating should be determined. The AS/NZS 1580 series of standards Paints and related Materials - Methods of test lists a large number of specific test methods for assessing paint properties. The methods cover tests for raw materials, liquid paints and paint films on substrates. A number of tests relate to evaluating the performance of paints used on the exterior of buildings. These include visual properties, such as colour and gloss, as well as physical parameters including hardness, blocking resistance and adhesion. Two test methods specifically cover the weathering performance of coatings Resistance to natural weathering and Resistance to artificial weathering (carbon arc type instruments) is a guide to assessing paints systems after exposure to natural weathering. Other methods including , cover the actual assessment of a coating after exposure testing. Some of these methods can also be used after accelerated weathering. AS/NZS 1580 does not require a set exposure time or that coatings meet specific performance ratings after exposure. Other Industry Standards In light of the lack of specific performance requirements for coatings in local codes and standards, de facto standards have been developed as alternatives. In Australia the Australian Paint Approval Scheme (APAS) evolved originally to provide Government Departments involved in the purchase of paints for state and federal buildings with confidence in the performance of their purchases. The Paint Approvals Scheme (PASS) in New Zealand had a similar background. Both schemes have found a wider client base in recent years reflecting the usefulness and market need for recognised paint performance assessment schemes. Further information on APAS is provided in Don Bartlett s paper. Customer expectation versus minimum code requirements With a performance-based code where the health and safety of the occupants are the primary goals, aesthetics and general concepts of quality (except where they affect compliance with any relevant NZBC clause) are not considered. The concept of products which suffer obvious deterioration over their life time, but still continue to meet code requirements is a reality under this regime. One of the main problems that arises is the difference between minimum building code requirements and the public/owner s perception of a reasonable life-time for a building or material.

7 Previous building regulations have always implicitly included a degree of customer protection, and thus building inspectors tended to enforce an unquantified but generally acceptable level of quality. For most common coating applications, the improved performance of modern coatings has led to a general consumer expectation of a coating life well in excess of the 5-year criteria which most often applies under the NZBC. The exception to this tends to be clear coatings or stains used on exterior timber claddings. The wide range of products sold for this application and the claims made by suppliers of some fringe products has resulted in a mis-match between performance and expectation in some cases. Most problems are associated with clear and semi-transparent film forming products and low build or penetrating stains. Some early products in the categories above failed to perform up to the manufacturers expectations and were withdrawn from the market. Others performed as expected but failed to meet the consumers expectations. This in part was due to a lack of detailed service life data on the products themselves and partly due to the difficulty in ensuring that accurate service life information was passed to the consumer through the retail supply chain. The performance of some systems was also extremely sensitive to the final film build and timber condition. Attempts to re-dress this situation by including very detailed application data on cans also proved less satisfactory than hoped for. Instructions which required the user to be confident of a certain thickness in microns of dry film being achieved were not really practical given the knowledge of the end user. As well as unexpected failures and a shorter than expected life to first maintenance, consumers were also caught out by the varying maintenance requirements of different timber coating products. Products with a similar appearance such as Madison style stains, alkyd-based stains and flat acrylic stains tended to behave quite differently. Many people expecting the simple maintenance regime needed for Madison stains did not expect the 1-2 yearly re-coat intervals needed to keep the appearance reasonable. With alkyd and acrylic stains, the 2-4 year life was better but, in many cases, maintenance required that the coating be stripped back on exposed faces before recoating. In practice, this has proved more difficult than expected. Subsequent to these problems arising, major manufacturers have taken steps to ensure that products are much better labelled or have removed those that consumers continued to misuse or complain about despite the clear labelling. Imported Products A wide range of products continues to find their way to the market from importers and smaller local companies who make impressive performance claims. Product descriptions can also create confusion where terminology commonly used in one country has a different meaning in another. There is often little reliable test information that the consumer can use to ascertain whether these products will perform as claimed, and whether they will do so in the southern hemisphere. It is becoming common knowledge that the closer approach to the sun, lower levels of pollution and high annual humidities in coastal regions (where most buildings are

8 located) mean that degradation of polymers occurs more quickly in New Zealand and Australia than in northern Europe (Trebilco, 1997). This has a significant effect on the expected service life of polymeric products. Differences in test protocols between manufacturers in different countries also contribute to difficulties in interpreting and comparing test results supplied with imported products. For example, use of different substrates in Australasia and Europe and North America can substantially affect the performance of coatings. Timber is particularly sensitive with moisture movement, coating adhesion and UV/moisture resistance varying substantially among different species. Western red cedar for example, shows rapid surface deterioration in as little as 4-6 weeks in New Zealand (Bennett, 1996), leading to poor paint adhesion. Variations in exposure orientation, climatic conditions and exposure periods are also important variables, which will influence the results of weathering tests on coatings. Conclusions Problems encountered with coatings can be caused by a wide range of variables many of which are specific to individual projects. A range of generic coating problems can be specifically attributed to inadequate or inappropriate product testing prior to release on the market. Limited use of industry standardised test procedures also makes it difficult for consumers and specifiers of coatings to make informed choices on product selection and to be confident that the coating system will perform as expected. This has led to problems in the past. The move to performance-based codes in New Zealand and Australia places the onus on suppliers/specifiers to provide evidence of appropriate performance of coatings. The current versions of the BCA and the NZBC do not reference any specific coating standards as a means of showing compliance. The opportunity exists for the coatings industry to develop suitable documents that can fill this role. These documents will also provide a valuable means of enabling manufacturers to differentiate their products from inferior ones and provide the consumer with a higher level of confidence in the performance of specific coatings. REFERENCES Bennett, A. F Performance of coatings on weathered timber. Surface Coatings Australia. Vol. 33. No 8. August. Building Industry Authority The New Zealand Building Code Handbook and Approved Documents. Standards New Zealand, Wellington, Australian Building Codes Board Building Code of Australia. Vols I and II. CHH Australia Ltd. Sydney. Standards Australia Paints and related Materials - Methods of Test. Part Coatings - guide to assessing paint systems exposed to weathering conditions. AS Sydney.

9 Standards Australia Paints and related Materials - Methods of Test. Method Resistance to natural weathering Coatings. AS Sydney. Standards Australia Paints and related Materials - Methods of Test. Method Resistance to artificial weathering (carbon arc type instruments). AS Sydney. Standards Australia The painting of buildings. - 3rd ed. AS2311. Sydney. Standards Australia Methods for fire tests on building materials, components and structures - simultaneous determination of ignitability, flame propagation, heat release and smoke release. AS1530 Part 3. Sydney. Standards New Zealand Timber and wood-based products for use in building. NZS Wellington. Standards New Zealand The painting of buildings. NZS Wellington. Trebilco, N. L How does New Zealand UV rate? BRANZ Build. June. Pp Judgeford.