Civil Engineering Reference
In-Depth Information
Chemical stain is based on a colour reaction with substances in the timber and
is used mainly on wood such as spruce or pine. Tannic acid can be used. Lye
treatment is also in the same category. (See also 'Bor salts from borax and
boracid' and 'Green vitriol', p. 440.)
Water based stain is made with pigments that are soluble in water. Modern
exterior stains usually also contain metal salts such as cobalt chloride, copper
chloride, potassium dichromate, manganese chloride and nickel chloride, in
order to impregnate the wood. Several ordinary pigments can be used in the
stain; but even bark or onion peelings are used as stain colours.
Stains are the least resource-demanding treatments. They are also relatively
problem free in production and use. The exceptions are water-based stains with
metal salts added. These are usually poisonous, and can seep into the soil. The
same can be said for the waste from these stains with added metal salts; they
should be deposited at special tips. As far as the other products are concerned,
re-use, recycling, composting and dumping are all relatively problem free. It is
only the addition of poisonous pigments that reduce the quality of an otherwise
very positive environmental profile.
Recipes for chemical stains
Recipe 1: Normal stain
10 g tannic acid is dissolved in 1 litre warm water. The stain is applied cold. It is usual
practice to then apply a second layer consisting of a solution of 10 g potash (K 2 CO 3 ) in a
litre of water. The colour is light grey-green.
Recipe 2: Lye stain
5 g of tannic acid is dissolved in 1 dl lukewarm water. 50 g potash is dissolved in 5 dl hot,
almost boiling water, and 4 dl cold water and 1.25 dl lye solution (12 per cent lye in water)
are added. The tannic acid solution is mixed with the potash solution. This must be pre-
pared in a stone vessel. It gives a stronger grey-green tone than the first recipe. The final
colour emerges after eight to 14 days. The stain should stand a few days before use. Lye
stains are highly alkaline, and protective clothing must be used.
Recipes for water-based stains
Recipe 1: Onion peel stain
The onion peel is boiled in water for 15 minutes and to a weak pink colour. The solution
is applied to wood, giving a faint yellow colour.
Recipe 2: Bark stain
The bark to be used has to be gathered during the summer. The colour is extracted by
pouring a 5 per cent soda solution over the bark and letting it stand for four weeks. For
250-500 g bark, use 250 g soda and 5 litres boiled water. After four weeks the mixture
has a very strong smell, but after an hour's simmering the smell disappears.
A brown colour comes from beech, apple and spruce bark and a yellow colour from
poplar and cherry bark. The latter needs 10 per cent soda solution. The bark of ash gives
a grey-green colour, and birch an apricot colour (using a 10 per cent soda solution).
Search WWH ::




Custom Search