BRE champions water-based paints

Trials at the Building Research Establishment (BRE) have cast aside any doubts about the performance of water-borne paints and varnishes in exterior uses - providing they are applied in the right weather conditions.1 But although water-based products would reduce air pollution problems, manufacturers say that a shift away from solvent-based coatings will have to be driven by consumer demand.

Paintmakers are under increasing pressure to reduce emissions of volatile organic compounds (VOCs). Most would prefer to meet the emission standards which are due to be phased in under the Environmental Protection Act 1990 later in the 1990s by substituting solvent-based products with water-borne and high-solid paints, according to Tony Newbold of the British Coating Federation. Installing abatement equipment will address only 5% of emissions - the majority of VOCs are emitted during use.

But the 1990 Act "is not the pressure that will force us to offer only exterior water-borne paints," according to Ray Leggetter of ICI Paints. "Until the new products, in our opinion, fully meet the performance standards expected by our customers we will offer both solvent and water-borne paints," he says.

Uptake of water-based coatings for external uses has not matched uptake in internal uses. This is partly due to a "prejudice" against water-borne paints in these more demanding applications, according to BRE. In both areas, only 2-5% of gloss trade sales are currently water-based (ENDS Report 222, pp 25-26 ).

For some time, BRE's advice has been that water-based paints can perform as well as solvent-based products. Its latest research reaffirms this view, and extends it to other external coatings such as primers and stains.

Trials have "consistently confirmed the ability of water-borne coatings to perform well outdoors, particularly on new wood," says BRE. One water-based paint, applied in a factory on joinery, has been on trial for 21 years and the results show "the excellent performance potential of water-borne systems." And their performance properties have been "substantially improved" over the last few years.

BRE also believes that water-based paints perform better than solvent-based alkyd paints in maintenance coatings. It found no indications of serious incompatibility problems - a common objection - when water-based products are applied to cleaned-up surfaces previously coated with alkyd paints. Durability can also be longer for these paints.

BRE's findings are not disputed by paint manufacturers. But the industry is also keen to stress the drawbacks of water-based systems in maintenance applications. These require the wood to be well prepared, while solvent-based paints are more forgiving, says Ray Leggetter. Taking such factors into account, solvent-based products last longer, he believes.

Both BRE and paintmakers recognise the problems of applying water-based coatings in adverse weather conditions. These can be "disastrous", says Ray Leggetter. If rain falls on the wet film, says BRE, there is a risk that paint could be washed from the surface. And in cold or humid weather the paint may not dry.

Because of these drawbacks, paint users and specifiers have to decide what paint to use depending on weather conditions. If only one paint is being specified, "we always say that solvent-borne paint is a safer bet", says Mr Leggetter, "although we actively promote water-borne paints over solvents in internal uses."

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