Green vitriol is a relatively harmless impregnating substance based on ferric sulphate. In liquid form it can irritate the skin and is slightly damaging to organisms living in water. A good impregnating solution consists of 10-13 g/litre of water, with a little alum added as a fix. Green vitriol is also a fire retardant and […]

These impregnating substances combine effectiveness against vermin with rela­tive harmlessness to humans. The emission period from an impregnated surface is as short as 10 hours, so the interior of a building will be risk-free after a couple of days. In Germany borax is the only one of the more effective poisons used indoors. It is […]

These have been used for surface treatment in many Swiss villages for hundreds of years, and the buildings have kept very well. A drier climate is, of course, part­ly responsible for their success, but this treatment deserves discussion. Impregnation with lye brings the resins and tar to the surface of the wood in the same […]

Bark extract often has borax and soda salt added to increase its antiseptic effect. The extract is poisonous to insects and fungus, even though somewhat weak. It is not dangerous to humans. Bark extract is not waterproof, and is most useful on exposed materials indoors. Extract based on birch bark has the best impregnat­ing properties. […]

Tar Wood tar is usually extracted from parts of pine that are rich in resin: the bole and the roots, which are burned to charcoal. It can also be extracted from other coniferous and deciduous trees. Tar from beech is widely used in mainland Europe. Modern extraction techniques give a very clear tar – previously, […]

Experience has shown that timber with a high content of tar and resins lasts longer than timber with a low content of the same. This is partly because the tim­ber is harder and partly because these substances have ingredients which are poi­sonous to fungus and certain insects. These natural fungicides and insecticides consist of, or […]

Substances which regulate pH are an effective way of preventing or removing mould attack. Mould will not grow if the pH level is higher than 6.0. The same can be said of insect attack. Exceptions are the fungus Merulius lacrymans and the longhorn house beetle. The pH-regulating materials to use are alkalines such as clay, […]

The application of a non-poisonous layer on the surface is mainly to protect the timber from mechanical wear and tear and direct solar radiation. Exposure to these can lead to large or small cracks which, in a damp area, can lead to fungus attack. Many different paints give a timber wall this sort of protection. […]