C O N T E X T 1 3 2 : N O V E M B E R 2 0 1 3 31 interior vapour barrier, will suffer extensively.The paint traps moisture on the inside of the walls, rotting the wood from the inside as the paint starts failing. In the UK, the belief is still that more coats of paint protect the timber better.The opposite is true: water will always find a way in, but the more coats on the surface of the timber, the more the water becomes trapped. The surface tension of linseed oil is lower than that of water, so linseed oil paints will penetrate the timber far deeper than water will. Linseed oil protects the timber from the inside out. Modern acrylic paints do not breathe enough and only form a surface coating. Wood replacement products, ranging from hardy-planks (clapboard exterior siding made from a cement compound) to vinyl siding do not resolve the maintenance nightmare.They simply shift it to a new material that still has to be maintained. Acrylic paints are thermo-responsive, being soft when hot and brittle when cold. Behaving differently in hot and cold weather means that if warmweather is suddenly followed by cold rain, the expansion and contraction of the paint is too great, potentially causing severe problems with paint adhesion, leading to the paint cracking and allowing water to penetrate and cause damage. Mildecides and fungicides were prevalent and popular until their environmental hazards were seen to outweigh their benefits. New formulations which retard the growth of the mildew and fungi are now being used. However, volatile organic solvents in oil paint and thinners have been categorised as environmentally hazardous. Historically, lead was often added to linseed paint. One comment I heard a couple of times during the IHBC annual school was that linseed oil paints only work when lead is added. It is true that lead forms a great accompaniment to linseed oil paint, but of course we now realise that the use of lead is undesirable for health reasons. Fortunately, there is another alternative. The addition of zinc white provides almost the same benefits but without the harmful side effects of lead. Zinc white, mixed in the right dose and in the right way with other pigments, provides superb protection against mould-growth. However, if the dose is wrong or the pigments are mixed with the oil incorrectly, linseed oil can become sticky and the colour may be unstable. The best results are obtained by applying linseed oil paint as a whole system to untreated substrates. This allows the oil to penetrate the surface and protect the timber from within. Linseed oil paint can also be painted over existing paints. Chemically, linseed oil has a very small molecular structure; so small, in fact, that it can adhere to other painted substrates. However, it is important to recognise that the final coat is only as durable as the base coat it sits on. With the awareness of the dangers of petroleum products to the environment, the paint industry is entering a new era.The use of binding materials made from alkyd oil instead of natural boiled linseed oil means that the use of synthetic resins, such as acrylics and epoxies, has become prevalent in paint manufacture.Acrylic resin emulsions in latex paints, with water thinners, have also become common.Most water-based paints also use these petroleum-based emulsions. Legislation has been drafted to eliminate petroleumbased oil paint from the market completely and to ban solvents in paint. Now might be the time to redress the balance and return to a completely renewable, natural product, which has an almost unlimited lifespan and where the maintenance is only every eight years or so, with nothing more than the application of some more linseed oil. Although the UK flax-pressing industry vanished back in the early 1960s, there has been a resurgence from the heartland of linseed paint production – southern Sweden. Since the 1980s, the Swedish open-air museumKulturen (www.kulturen.com) in Skåne, working with specialist manufacturer Ottosson Färg, has conducted extensive research into the use of linseed paint on century-old buildings.Their work has shown that linseed paint still offers the most durable, long-lasting protection for timber, minimising environmental impact and enhancing the natural beauty of timber. Michiel Brouns of Histocolour is a specialist supplier of linseed paint products. Hallanbergs Country House: pine timber houses can last many centuries when painted with linseed paints.
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