The year 2000 – a new century, a time for reflection, taking stock of successes, failures, achievements and for contemplating the future. At the start of the last century, wood coating technology enjoyed a period of stability, with little energy expended on new or improved coatings. Then, joinery was made from large sectioned, slow-grown wood and protected with flexible lead based paints which seldom showed the type of failures that have become characteristic of their modern day equivalents. One could be forgiven for saying that, seeing the frequency of failures, today’s coating technol-ogy has been retrograde.
The reasons for this incongruity can be traced to a combination of changes in legislation and in attitudes to silviculture whereby timber has changed from being an abundant building commodity to a scare and valuable resource. As a consequence, definitions of ‘acceptable timber quality’ were redefined to maximise a shrinking resource.
Against this backdrop, the wood coatings industry was forced to adapt and manufacturers responded with new types of coating systems which included phenolic and nitro-cellulose based coatings, acrylic and alkyd based systems and polyester products. These developments coincided with a change in consumer attitudes. Timber was seen as a valued resource, leading to translucent stain products – which were vulnerable to premature failure – as alternatives to traditional oil-based opaque coatings.
Today, the coatings market has changed radically. The consumer has a bewildering choice of products set in a marketing environment of claim and counterclaim, with each manufacturer vying for market share. Competitive pressures have forced them to develop alternative coating strategies to extend existing markets and increase commercial penetration.
In many ways history is repeating itself – where health and safety controls signalled a radical change during the 20th century, environmental legislation has set in motion changes at the start of the 21st. These have taken the form of the so-called compliant coatings – that is low VOC (volatile organic compound) coatings. This has resulted in an upsurge of water-borne dispersion, hybrid products and high solids coatings.
The VOC issue has not only spawned a rash of new and sophisticated formulations but has also invigorated interest in alternative application technologies. This is clear from current developments in radiation cured application technologies for flatstock as well as research initiatives on cold plasma coating where polymeric films can be deposited on wood in a gas medium under low pressure with good results. Further developments in powdercoating systems for wood products are being examined. These claim to have the potential to streamline manufacturing operations by replacing multi-coat applications of conventional products with a single powder application.
Formulation and process developments have, therefore, progressed to the point where a wide range of sophisticated coating alternatives is available for wood. However, these can go only so far in improving performance and often count for little without comparable developments in application and processing technology that can bring significant benefits through better film uniformity. This has been shown to be true with recent investments in modern factory pre-finishing processes leading to renewed consumer confidence in wooden joinery as a result of better quality and performance, achieved by tighter control over the application process.
The idea that coating performance can be improved by considering application methods and better substrate preparation has recently gained a great deal of ground. Surface modification of timber as a precursor to coating belongs to this category of developments. Chemical treatments such as acetylation are more frequently used as a means of stabilising wood substrates before coating and minimising the physical stresses which cause film failure in service. Claims are also being made that high temperature treatment of wood may be an alternative method of stabilisation, with the advantage of not requiring chemicals.
Work is also being carried out to examine the benefits of treating wood with flame plasma to improve adhesion properties of coatings. In addition, the use of grafting chemicals, either on the wood surface or as an integral part of the coating formulation, to act as adhesion promoters and UV stabilisers is showing promise.
The diversity of these developments and approaches shows that there has been considerable activity in wood coatings in recent years, with no sign of abatement. Technical innovations bring with them the need to update or develop test methods and standards. In today’s commercial climate, the substantial investment in new test methods signals the healthy state of innovation in the woodcare sector. This bodes well for the future of wood as a building material.
However, innovative developments are no insurance against bad practice and, despite these advances, problems related to site malpractice are commonplace.
One of the major causes of customer dissatisfaction within the woodcare sector today is the lack of adequate control over the specification and application of exterior coatings to wooden on-site joinery. In a report commissioned in the late 1970s entitled Blight on Britain’s Buildings, Professor Ivan Seeley attributed the principal cause for the replacement of windows in UK housing to poor on-site coating and application practices. Over two decades later, the situation has remained virtually unchanged, with the routine replacement of rotting wooden window joinery commonplace – in some cases fewer than 12 months after completion and handover.
The fact that building malpractices have created an untenable consumer perception problem for the UK building industry is evidenced by the recent launch of the government’s quality mark initiative in an endeavour to outlaw cowboy builders. The scheme aims to raise the standard of workmanship in the domestic repair, maintenance and improvement sector, protecting consumers through a third party warranty. While the scheme has not been proposed specifically with coatings in mind, it nonetheless offers a salutary reminder that achieving improvements in coating performance is as much an education issue as a technological one.
Today far more emphasis is placed on providing best practice guidelines than ever before. The cornerstone of this approach comes with the timely release of EN 927-1 1997 – Paints and varnishes: coating materials and coating systems for exterior wood, classification and selection. The significance of this standard is that it relates coating selection with component type and exposure situation. The hope is that this approach will induce greater awareness that wood finishing is as much a part of the building process as the construction itself and that considering all the links within the building chain is necessary to good coating performance. The specifier now has a tool to help him give the end user the best long-term performance.
In this context, the performance of wood coatings is inextricably linked with good design practice. Many of the present initiatives to improve performance have focused on more effective component detailing to relieve some of the protective burden from the coating.
The choice of complementary products in the joinery manufacturing process has also played its part in developing an integrated approach to improving coating performance. This can range from the choice of glazing system and preservative type through to the selection of the most appropriate wood species (see flow diagram).
Changes in consumer trends have also impacted on the coatings industry and are dictating future developments. This is well illustrated in the wood flooring industry where rapid growth has been paralleled by increasingly sophisticated floor seal products with shorter drying times, good levelling and translucence properties, low toxicity and better wear resistance in response to end users’ demands.
Similar challenges will inevitably arise from the popularity of timber decking systems where aesthetic and functional needs must be combined with consumer appeal and good slip and abrasion qualities.
In conclusion, the rate of change taking place within the wood coatings industry is remarkable and reflects the importance with which the industry views wood as a substrate. However, the relationship is far from one-sided. It is mutually supportive where the benefits to the coatings industry are matched by those to the timber industry. If current levels of research and development are sustained, there is little doubt that wood, as a building resource, will survive well into the next century and beyond.
Related Files
Interaction of Wood Coating with other Factors
