Solvents are used to thin out thick paint mixtures and make them more penetrative; they vaporize from the surface after painting. In certain types of paint, the binder itself is capable of dissolving the paint to a satisfactory consistency, as in the case of cold pressed linseed oil, heated wood tar, etc. A few paints can be dissolved in light oils, such as fish oil, whilst some paints dissolve in water. Many paints, especially newer types, and binders of natural resins and wax, must have an organic solvent added. Alcohol can be used in several mixtures, e.g.

in natural resin varnishes. However, most common are mineral spirits and turpentine.

• Mineral spirits are distilled from crude oil. The main constituents of the most common mineral spirits are xylene, butanol, toluene, ethyl acetate and methanol. A special mixture is marketed as white spirit, and is now the dominating organic solvent in paints.

• Turpentines are distilled from wood tar or pressed from orange peel. Sulphate turpentine is produced from sulphate cellulose. Before crude oil based solvents came on the market at the beginning of the twentieth century only turpentine was available. It is still much used for dissolving natural resins and vegetable oils.

Water is without doubt the optimal solvent, environmentally speaking. The organic solvents have considerable environmental implications. Whilst mineral spirits have crude oil as their source, turpentine is based on renewable plant resources. The energy use in production is also higher for mineral spirits and the solvents emitted have a global warming potential three times that of carbon dioxide. Turpentine is considered climate neutral since emissions are equivalent to the carbon dioxide originally taken up during the growth of the plants used as raw material.

On the building site, vaporizing of mineral spirits represents a major problem and is associated with nerve damage and other serious health problems. Many painters refuse to paint with these solvents. Spirits with less acute emissions are the isoaliphates, which are obtained by boiling crude oil at a specific temperature. The vapour from turpentines is normally even more irritating to the mucous membranes than those resulting from mineral spirits. One constituent, pinene, can cause allergies. There is, however, no proof that long-term exposure to turpentine can have the same chronic effects on the nervous system as mineral spirits.

In freshly painted buildings the solvents release gas for shorter or longer periods depending upon the drying conditions of the building. Solvents vaporize completely, so there are no waste problems.

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