The paint should not be used in bathrooms or similar areas, or on surfaces exposed to a great deal of wear and tear.
When painting on plaster it is usual to wash the surface with a thin solution of green soap, consisting of 1 part green soap to 50 parts water.This should sink in and dry in order to give the glue paint a chance to penetrate evenly into the plaster.
Painting should be done wet-on-wet so as not to be blotchy. Before being added, the pigment should be mixed with a little water tothe consistency of a thick colour paste with no lumps.
RECIPE: GLUE PAINT BASED ON BONE GLUE OR HIDE GLUE (10 LITRES)
Theingredientsare200 gdryboneorhideglue,5 litres of water, 10 kg powdered chalk and pigment.The paint is prepared inthefollowing way:
1. The chalk is first soaked and left in a bucket overnight without stirring.
2.The powdered glue is treated likewise and left overnight, with water just covering the glue. It is then carefully warmed in a water bath until dissolved.
3.The glue is poured into the chalkand stirred well.
4.The pigment paste should be mixed in. Certain fatty pigments are not easy to dissolve, but this can be improved by adding a teaspoon of alcohol, which breaks down the surface tension. The stronger the colour required, the more chalk must be replaced by pigment.
Casein paint is produced as an emulsion, the milk protein acting as binder. Pure casein products are not water repellent and should be limited to indoor use. When reacted with lime, either when mixed or when painting on surfaces containing lime, a more water resistant paint is achieved, see 'Lime/casein paint' (page 394). This is also the case with emulsions of casein paint and linseed oil, see 'Linseed oil/casein paint' (page 402).
A drying oil dries in the air, while at the same time keeping its elasticity. The most common drying oil is linseed. Hemp oil also provides good quality. To some extent soya oil, olive oil and fish oil can also be used, but these are not actually drying oils.
Linseed oil dries by oxidizing in air and is transformed to a strong and solid linoxine. This oil has been used in paints since the beginning of the seventeenth century and can be used on wood, earth, concrete, plaster and to a certain extent, steel. Linseed oil is also used on stone facades to close the pores and protect it from aggressive air pollution. Plaster and concrete should not be painted during the first year, since moisture emerging from inside the underlay can push the paint off. Oil paint can be produced in matt, half-lustre and full lustre form. The half-lustre and lustre types are very strong and easy to clean. Linseed oil products are generally water resistant with moderate vapour permeability.
Cold pressed oil is seen as being of higher quality than hot pressed oil. Cold pressing, however, only frees about 30% of the oil in the seeds. In hot pressing the seeds are finely ground and pressed while warm, which substantially increases the yield. The oil can also be used as it is, or boiled. Raw linseed oil is probably more robust, especially when cold pressed, but it dries very slowly because of the large amount of protein substances it contains. It is therefore mostly used out of doors. Boiling linseed oil to 150 °C removes the majority of the protein, making the product dry more quickly. The paint can be used both indoors and outdoors.
Stand oil is linseed oil that is boiled without air to 280 °C and thereby polymerized. It is considered to be firmer and more elastic. It also dries quicker than the other types. Even so, drying time is a problem with linseed oil products. In factory produced oils, drying agents (siccatives) are therefore added to a proportion of about 0.5%. This also applies to products for outside use, even if the drying time there is not too critical. For indoor use, it is normal to add drying agents to all qualities of linseed oil, but drying oils such as tung oil and cedar oil can achieve the same purpose. Another way to reduce the drying time is to use linseed oil in a water-soluble emulsion with casein glue, collagen glue, starch or egg.
Linseed oil paint often has fungicides added but this is not necessary for interior painting. Emulsion paints are dissolved in water whilst organic solvents are often added to pure linseed oil products to increase penetration and spreading rate. This is usually unnecessary for easy-flowing oils such as cold pressed linseed oil. The amount of solvent varies from about 10 to 30%, and is much lower than the equivalent in alkyde paints. A process for treating floors using highly refined linseed oil has also been developed that does not require drying agents or organic solvents. Application is then performed with a polishing machine.
The raw materials for drying oils are renewable and environmental problems relating to their production are minimal. Products containing a high percentage of organic solvents are an exception to this, and present a risk, especially for painters.
Within buildings, linseed oil products can be regarded as less problematic. During the curing period there will be an emission of oxidation products, mainly aldehydes, which can temporarily irritate the respiratory system but without any known long-term effects (Knudsen etal., 2004). Fresh paints and oils containing organic solvents can emit irritating substances. Pure linseed oil products have moderate vapour permeability. Their porosity increases with time, but will still be too small for the moisture buffering capacity of the underlayer to be fully used. An exception is a product where linseed oil is in an emulsion with an animal glue, which is considerably more vapour permeable. Products based on vegetable oils do not cause electrostatic charging.
Materials treated with vegetable oil products are difficult to clean, which will reduce the re-use value. Products with no hazardous substances added can be composted or burned in ordinary incinerators.
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