MAKING AND USING
TRADITIONAL PAINTS
AND
FINISHES.
An article
originally written for "Rural Wales" the magasine of CPRW
In the previous articles I explained the important breathing quality of the walls in traditional buildings. This enables any water or dampness held within the wall structure to continually evaporate from the exterior surface thereby reducing internal dampness. This essential process is jeopardised if a non-breathing surface like a cement render is applied to an exterior wall. For this reason lime mortars should be used when restoring or repairing the walls of traditional buildings.
However, there are many instances when exterior walls were painted or need to be painted for decorative reasons. In fact most stone built cottages in mid Wales were regularly painted white, creating a landscape bespeckled with gleaming white faces like stars in the evening sky. It is as wrong to strip these traditional buildings of their colourful exterior as it is to cover the stone-craftsmanship of North Wales stone with renders. Return to Conservation Index
Because of the need to retain the breathing effect, it is necessary to use traditional paints and not modern plastic coatings that form an impenetrable skin. Vinyl is commonly used in the manufacture of modern paints and has some most undesirable qualities. It forms an impervious skin that blisters with any hydraulic movement, and also once applied, is very difficult to remove. It also gives off the poisonous gas, vinyl chloride, which is thought to be an irritant and carcinogenic chemical.
The most common type of traditional paint used on exterior walls is lime wash. This is both easy and cheap to make by simply diluting a lime putty with water to obtain a creamy consistency. For external work, melted tallow may also be added to improve weather resistance. Before applying the paint, the wall surface should be checked; loose paint removed, and any large holes filled with a lime mortar mix. The paint can then be applied liberally by brush, and should be worked into all cracks and crevices. A lime wash will dry in about two hours, but takes longer to fully harden by the absorption of carbon dioxide. A single coat is not opaque enough to obliterate a raw wall surface, and several coats may each be applied after 24 hours.
Basic white lime wash can be tinted with earth pigments or natural dyes made from tea or onion skins. Lime wash gives a richness of illuminescence that cannot be matched by any other paint, but it cannot be wiped like modern paints, and will need re-coating every year or so to retain the characteristic brilliant clean finish. Lime wash can also be used internally, for living areas, barns and workshops, where its high reflectivity will greatly improve the illumination of rooms with small windows. Lime wash can be passed through a fine sieve in order to achieve a smoother interior surface. When used on interior walls it will reduce the spread of surface mould because of its high pH. and will generally eliminate condensation. Return to Conservation Index
Where a more durable interior wall paint is required a casein paint or a simple distemper can be made. Casein is a protein found in milk which is used commercially to make powerful glues. Its durability will be familiar to anyone who has tried to remove milk splashes from a child's high chair! It was also used traditionally to make a basic paint that can be wiped clean but not scrubbed. Casein powder paint can be purchased from specialist suppliers or it can be made by mixing raw casein powder with water with a small amount of ammonium carbonate. This may take from 30 to 60 minutes to thicken into a brushable paint. Like limewash, it can be tinted with pigments or dyes. Because of its improved resistance to washing, casein paints are suitable for children's bedrooms, bathrooms and small kitchens.
Distemper is a glue-size based paint which was used for decorative interior painting. Sadly, Walpamur distemper is no longer readily available. Distemper is suitable for interiors where a flat colour is required or where murals, freezes or stencilled patterns are applied to interior walls. A glue-size is first made up by soaking rabbit skin glue granules overnight in water. The gelatinous lump is then heated in water using a double boiler or old fashioned glue pot. Two ordinary sauce pans can also be used, with a water jacket in between, so as to prevent the glue-size from actually boiling. Stir the glue as it dissolves into the water, to obtain a clear, syrupy size. To this, add ordinary whiting powder, adding enough to give the paint the amount of body that you require. Keep stirring whilst adding the whiting to dissolve all lumps. Further water can also be added to balance the consistency. Finally, add pigments to achieve the colour you require. This paint must be kept warm whilst in use, but once applied to the wall will soon harden to provide a very durable yet traditional wall surface. Small quantities of special colours can be made up for decorative painting or stencilling work. A clear, thin rabbit-skin glue-size can also be used as a glaze over any paintwork, to increase its richness and durability.
In addition to traditional paints that can be easily made as needed, modern paints are now available that do not form a vinyl or plastic skin. The 'Auro' range of paints are entirely made from selected natural materials, but are quite expensive. They are not traditional paints but have the advantage of causing the least irritation to people sensitive to chemicals. 'Keim' mineral paints also retain breathing qualities and use water glass (sodium silicate) as a medium. This penetrates the silica contained in stone or concrete and provides a very durable and weather-proof external surface. However, it is impossible to remove and is quite expensive, but is very suitable for buildings where a low level of maintenance is required.
Originally prepared as an article for RURAL WALES, the magazine of CPRW.
Written by John Nicholson, Tanrallt, Rhostryfan, Caernarfon, Gwynedd, LL54
7NT.