Paints

Paints have three constituents: pigment for colour, a binding substance to hold the particles of pigment together and a solvent to enable the mixture to flow freely. It is the solvents which are the main problem since they are designed to evaporate. Most of the solvents used come into the category of volatile organic compounds (VOCs) and are aggressive pollutants. It has been calculated that over 500 000 tonnes of solvent are released into the atmosphere globally each year (Harland, E. (1999) Eco-Renovation, Chelsea Green Publishing Company, Vermont, USA, revised edition). Another statistic is that organic solvents are responsible for 20 per cent of the hydrocarbon pollution in the atmosphere and second only to motor vehicles (Berge, B. (2000) Ecology of Building Materials, Architectural Press, Oxford).

It is the solvents which derive from the petrochemical industry that are the most toxic and are implicated in the phenomenon of off-gasing. This may continue for a considerable time with sometimes serious health consequences. (A comprehensive list of surface treatments and their solvents is to be found in Berge, ibid., p. 405 and also Edwards, L. and Lawless, J. (2003) The Natural Paint Book, Rodale Press, available from the AECB book service: www.aecb.net.) There are alternatives such as those containing natural resin emulsions. They appear much the same as conventional petrochemical emulsions, are as easy to apply, are solvent free, do not have the pervasive smell of chemically based paints and are also biodegradable.

Humidity

The choice of paints and varnishes can have an impact on the level of humidity within a building. Temperature is the key factor in determining how much moisture the air can hold. At 20°C air can hold 14.8 g/m3; at 0°C it can only hold 3.8 g/m3. On average a living room contains 5-10 g/m3. Fluctuations in temperature will alter the carrying capacity of the air and may result in condensation. It is important that the materials of the walls can absorb much of this moisture which means the use of hygroscopic materials, that is, materials that can take up moisture. Such materials act as a stabilising agent, keeping the humidity level reasonably constant. In other words, hygroscopic materials have a damping effect on moisture fluctuations just as thermal mass regulates temperature (Berge, ibid., pp. 251-253).

It is recommended that internal walls should be finished in hygroscopic emulsion paint over plaster. This ensures that excess moisture can be absorbed by the plaster and masonry wall, releasing it when the internal humidity level creates imbalance. A further benefit is that water vapour carries some gas contaminants like nitrogen oxide and formaldehydes. When the water vapour enters the hygroscopic materials these chemicals may be deposited and broken down giving these materials a degree of air cleansing capacity. However, the transfer of moisture will not happen if wall surfaces have impermeable finishes like oil-based paints or varnishes, plastic wallpaper or even wallpaper fixed with plastic-based pastes. Internal walls need to breathe, otherwise condensation is virtually inevitable.

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