By Peter Maitland Hood
Maitland Hood was a consultant conservator, historian and technologist of historic houses
and the materials of the old tradition, surveying works of repair, improvement, maintenance
and protection. He was also the director of production at The Real Paint & Varnish Company,
a leading manufacturer of traditional painting and decorating materials.
Paint has often been thought the least important of matters, whereas in reality for protection and beautification, it is quite the opposite. Paint is all around us, yet few know much about it. The following answers to some frequently asked questions will hopefully provide some further background to this important area:
Q. What is modern paint?
A. Before the last century, the painter and decorator or his
apprentice made all paint. The word described oil colour, mostly lead-based and used on woodwork
and distemper used on plaster work. Before 1834, the basic paste was hand-ground on a slab.
Then the introduction of cast-iron paint mills led to industrialists taking over production
on a huge scale, introducing new zinc-based paints and revolutionary emulsions, marketed
as oil-bound distempers, whose fineness was quite beyond the means of the traditional tradesman.
In the 1930's titanium was first introduced and soon replaced both zinc and white lead as
a basic white (it is in fact an extremely light blue). At the same time, plastic paints appeared
with synthetic colorant replacing traditional pigment and linseed oil while white spirit,
a petroleum derivative, replaced spirits of turpentine. Today's paints are mostly based on
plastics: synthetic latex, vinyl or polyurethane and acrylic resin.
Q. What is traditional paint?
A. Before the discoveries and inventions of the nineteenth century, houses, furniture and paints were all similarly porous, elastic and survived by an equilibrium between hot and cold, wet and dry. The paints were carefully designed, formulated and hand-made by the experienced workman, relying on knowledge handed down through the centuries, common sense and personal observation. Paints which lasted were those which were water permeable and elastic. In this respect, oil paints based on white lead were unsurpassed. Their permeability came in part from the white lead base itself, which constitutes more than 80% of the paint, being hydrophilic (water loving). Elasticity came from the plasticity of the lead and the property of the oil. The combination of white lead and linseed oil makes a lead soap which combines these factors. Being hand-ground on a slab, the degree of fineness and amount of sharp particles that survived, were a characteristic of certain colours. As long as the particles were of a similar size and contained sufficient spherical particles, application by brush was no problem. White lead paints can be tinted with most traditional pigments and being translucent, provide remarkably good imitations of natural materials such as marble and stone. Distemper, the most common traditional coating used for plaster, is based on chalk whiting and bound with animal skin glue. Pigments are precipitated onto the whiting or mixed in the glue and added with water as a thinner. Whereas in traditional oil paint the colour is saturated with oil and looks deeper, in distemper the colour is a generally a hue, though the whiting can be left out presenting the natural appearance of the pigment. Distemper is quick drying and if made by a competent manufacturer or experienced workman, does not powder, come off (unless scrubbed) and can last for centuries. It is not suitable for bathrooms or small kitchens. Traditional oil paint is slow drying if it is going to last, with the linseed oil taking about 72 hours to dry in warm, dry conditions. This can be advanced if the pigment contains oxygen. The addition of synthetic driers shortens its life.
Q. What are the benefits of traditional paint?
A. If manufactured in the way of the old tradition, the pigment is ground into the binder in a way that avoids blunting the edges of the pigment and making it too fine and therefore dense. The binder is processed in ways that ensure that the paint remains elastic as long as possible and each coat is specially formulated to make a bond with that preceding it, so that a lamination of paint layers is made. The first coat is designed to make a good attachment to the substrate and reduce absorption of binder from consequent coats. If manufactured carefully and applied by brush thinly, traditional paints prove not only permeable (allowing the building or piece of furniture to 'breathe') but also extremely durable. When it comes to maintenance, one or two coats are all that are required to replace coats lost to weathering or wear.
Q. Is lead paint dangerous?
A. Lead paint will not leap out and bite you and emits no dangerous chemical or gas. It produces a chalky surface in its mature state but this is quite sublime lead sulphate. However, lead paint containing white lead does present a hazard or risk to children and young animals if they lick it, chew it or ingest it. White lead is readily absorbed by water and therefore enters the bloodstream quite easily. It effects the nervous system, as does alcohol. Until they are eighteen years old, children are in a constant state of development and any distortion of their nerve system may be permanently damaged by continuous ingestion of white lead. Where there is concern, old paint is best overcoated with a modern, lead free alternative. Removing lead paint risks dust and environmental contamination, increasing the risk.
Q. I have an old house. Can I use lead paint?
A. You can still use lead paint as long as it contains no white lead (lead carbonate) or grey lead (lead sulphate). Red lead remains unsurpassed as a primer and stopping for historic ironwork. If you own a Grade I or II* Listed Building (Category A in Scotland) or a Scheduled Ancient Monument, and you have to repair or maintain white lead paints, the use of lead paint is lawful and the paint can be manufactured and supplied. A simple declaration has to be made to English Heritage, Cadw or Historic Scotland (depending on which country the property is in) on a standard form, so that they can confirm the listing.
Q. My house is listed Grade II. I want to restore its historical integrity and permeability. What should I use?
A. There is no doubting that lead paint would almost certainly have been used originally and that it is unsurpassed for appearance and long-term conservation. However, there are good alternatives; the secret lies in the quality of the oil binder and thinner, as well as not using untinted white. Specialist manufacturers are able to offer appropriate alternatives. Whatever is used, even lead paint, will be new and of our time; true restoration being impossible.
Q. How can I tell if I have modern paint or traditional paint on my house?
A. If the paint is splitting and peeling, it is probably modern. The easiest indicator is weight: almost all traditional paint contained lead, so take a piece of loose paint off and feel it. Wash the hands afterwards before handling food. One can put the sample over a flame, taking care not to have an accident, and watch to see if liquid lead globules drop out. Maybe the paint is really well attached and you cannot remove a sample. If this looks old and has a chalky sort of surface, it probably is lead paint. Old lead paint shrinks into large 'checks' - i.e. there may be fine cracks at two-inch intervals, leaving an oblong piece uncracked. The cracks only require filling with at least linseed oil putty before recoating. Obviously the best overcoat would be the same paint but this may not be lawful (see above).
Q. What is the best way to remove old paint?
A. Unless paint is peeling, flaking or detached, it is probably best left alone and appropriately recoated. However, where old paint has become excessively thick and obscuring detail, old paint is best removed by dissolution. Burning or heating can lead to lead poisoning or damage to timber and glass; entire houses have been lost to fire caused by careless use of flame-guns ('blow-lamps'). Most solvents are strongly alkaline and act on the acidic oil binder, causing it to soften. A cheap but hazardous solvent can be made using caustic soda in hot water with cellulose wallpaper paste added to make a gel. This very corrosive mixture calls for full face and skin protection, chemical resistant clothing and goggles for personal protection. If this worries you or is impossible, you can obtain patent paint solvent from specialist suppliers or get firms to do it for you. You can also try boiled linseed oil, leaving it on for 24 hours - this can soften paint quite well enough, so that it can be scraped off. Before repainting, any alkali left on the surface needs neutralising with a weak vinegar/water solution.
Q. What is Lime Wash?
A. Lime wash is one of the oldest coatings known and generally used on stonework, plaster and brickwork as a cheap cleansing and disinfectant coating inside and out, a lightener for dark rooms, and a night-light margin for doorways. It was also used as an overall finish to suggest construction from marble, as intended in antiquity (classical Greek statuary and buildings were lime washed as a protective against destructive maritime salts). It was traditionally made from quick lime added to milk with a bit of salt as a preservative, or water with a bit of fat added for water-resistance. It was applied while still hot, using a special wide brush. Cold preparations can be used effectively; the best of these are based on traditional pit-slaked and matured 'lime putty' thinned with either milk and a preservative other than salt for indoor use, or water and tallow fat for outdoors. Both can be tinted with alkali-resistant pigments, some of which improve durability. A good lime wash should have the constituency of double cream.
Q. How can I tell if I have Lime Wash on my house?
A. Look carefully for a flaking part, or cut a bit of the coating off. If the section looks like an onion skin, made of many layers, it is probably lime wash. If it deepens in tone on wetting or when it rains, it is more likely to be lime wash, If the section sounds slightly metallic as well when dropped or tapped with a tool, it is almost certainly lime wash. On careful application of brick-cleaner (dilute hydrochloric acid - wear protective clothing and glasses) it should fizz and dissolve. If it is obviously old and doesn't seem to be lime wash (following the preceding tests) it may be Colour Wash.
Q. What is Colour Wash?
A. Traditional colour wash is generally based on an earth pigment and bound with either sulphates or alum or stale beer. It was generally used to match the best brick and even up the varied appearance of handmade brickwork, but it was also used as a cheap, renewable coating for cottages.
Q. What paint should I use to protect weatherboarding?
A. Traditionally, weatherboarding was treated similarly to boats. The earliest coating must have been closely related Stockholm Tar, originally made by boiling the resin from wood in huge vats close to the sawmills. The tar was applied to the new timber in several coats following a preparation coat of hot lime wash to make the wood 'hungry' and gives a brownish black, water-resistant finish. Following production of gas from coal in the nineteenth century, a black tar was readily obtained and provided a cheap and much used alternative. Lime based coatings mixed with milk and salts were frequently used where lime was readily available, but the movement of timber as it dried calls for frequent repair and recoating. Ochers were also used, bound by boiled linseed oil to make paint and often with fossil resin varnish added for extra protection. Spanish Brown, a flesh coloured pigment procured from natural haematite, was commonly used. A superior but more expensive coating was white lead paint, consisting of a Pink Lead Primer followed by up to seven coats of White Lead Paint, each specially formulated to make a single laminated coat with litharge (lead monoxide) incorporated as a drier. An excess of litharge reduced both cost and drying time and produced a grey stone colour. Woodworm rarely bores boarding originally painted with white lead. Since the general prohibition of white lead in paint in recent years, the preservative properties of this special historic colour and texture can hardly be imitated. It is safer to leave white lead paint in place and overcoat it with traditional oil paint using alternative white pigments. Spanish Brown and other natural ochers in oil paint with a variety of textures and finishes are available from manufacturers of traditional paints. The original colour often underlies later painting and can be identified by specialists in this field who know which are primers and undercoats.
Q. Can I apply Lime Wash to concrete render or gypsum plaster?
A. Modern concrete renders and plasters are too dense for lime wash to adhere on its own, but specialist manufacturers of traditional paints should be able to provide lime-based coatings with appropriate additives which will adhere well and prove quite durable.
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