Every day my team and I at Papers and Paints see confusion amongst members of the general public who come in clutching articles torn from the lighter weight “House Wonderful” type magazines, which urge them to create a “period feel” using “traditional” paints compounded of such things as whiting, buttermilk and a bit of PVA to make it stick. Furthermore every kind of surface can, it seems, be given this sort of treatment in order to create the “distressed palazzo”, “Mediterranean”, “Colonial”, or “Country House” look – all of which seem to be associated with the term “traditional.”
There is confusion, too, over the incidental cross-over between several of the traditional coatings and those that may be regarded as ecologically friendly. Certainly, a white lime wash and a soft distemper may be so regarded, but these qualities are often automatically extended to include all of the less modern paints, no matter what type or colour.
Unfortunately, because of the large amount of money tied up in this area of the decorating industry it is very difficult to find clear dispassionate advice shorn of profit-mongering. The merchants of snake-oil (or should that be peanut oil?) are still very much with us.
Perhaps it is the word distemper that causes the most confusion. Few are aware that this is a generic term encompassing several different coatings. There really is only one type that is of relevance to historical buildings – or any building for that matter.
Soft Distemper, as it is more commonly called, is excellent for the coating of elaborate decorative plasterwork or ceilings. Washed, finely-ground chalk, known as whiting, forms the main constituent. This is loosely bound with a water-soluble glue size usually made from animal bones, horns or skin, often nowadays going under the name of rabbit skin glue.
This is a coating that is made up by the decorator shortly before carrying out the work. In view of the animal glue content once it has been made it has a very limited shelf-life, going rancid after a short time even if refrigerated. By definition, therefore, one cannot buy a true soft distemper in a tin.
Soft distemper is applied by brush and can be removed with a wet sponge when dirty or in need of recoating. Its great advantage is that when applied to ornate plaster ceilings, for example, the detail is not lost as it must be removed before redecoration. An emulsion paint, on the other hand, would add yet another disfiguring layer that will eventually require removal.
As well as its permeability to moisture vapour, which makes it an option in areas inclined to mild damp, soft distemper has the added bonus of being cheap. It is easily made and applied, and can be laid on quickly, provided that an experienced decorator is at hand.
It is not durable however and is neither washable nor suitable for areas of heavy traffic, hence the modern name of soft distemper. As a result, in the nineteenth century, various binders were added to increase its resilience. The additives varied in type and efficiency, and would often have had a profound effect on the technical properties of the paint. One wonders how “breathable” Morley’s Rubber Distemper would have been?
One of the most common sorts of ‘improved’ distempers were the primitive emulsions known as Oil-Bound Distemper, Casein-Bound Distemper or more properly Water Paint. Note here the use of the word ‘emulsion’ to indicate a mixture of two liquids that normally cannot be combined – such as oil and water. It may come as a shock to learn of the very fine line between a bound distemper or water paint and an emulsion paint, as found on the shelves of many builders’ merchants.
By “oil-bound”, it is meant that the paint was an oil-water-emulsion, in much the same way that milk is. Water and oil were combined with a solution of soap or a caustic alkali (such as lime) which saponified the oil, and the mixture was agitated until the oil broke down into tiny globules which remained in suspension as an emulsion.
These early emulsion paints were generally supplied in a stiff paste, which was thinned with water to a brushable consistency for application. On evaporation of the water, the paint dried to a porous film, with the glue – often in the form of casein – acting as a temporary binder during the drying of the oil, which finally hardened the film so that it became moderately wipeable. One of these early brands, Alabastine, was also used as a plaster filler – a questionable advantage as far as a paint goes.
The current trend for labelling or referring to these primitive emulsion paints as distemper is storing a problem for the future. Lulled into thinking that the substrate can breathe under an historically appropriate and pleasingly matt coating it is frequently specified or employed by well-meaning house-owners. Unfortunately, these early form of emulsions had a number of weaknesses. Certainly they had a matt finish and some did have a degree of permeability to moisture, however they did not have the key advantage of soft distemper, and that is its reversibility.
Some years ago, when the Journal of The Traditional Paint Forum, commissioned the Paint Research Association to make comparisons between a typical trade emulsion paint and a Water Paint that was being sold as a distemper, it was found that there was scarcely any difference in the moisture vapour permeability of both systems.
These Water Paints reached their heyday in the mid twentieth century and are best remembered under such brand names as Walpamur and Duresco. Unfortunately, these early form of emulsions had a number of weaknesses.
As the ‘improved’ distempers cannot readily be removed, further coatings tend to be applied on top, and then within two or three schemes of redecoration the problems can start to occur.
The strength of the bond of water paint is less than that of oil paint and, although the coating has some resistance to water, it is absorbent nonetheless. The liquid in a new coat of paint applied on top will soften it to some extent and cause it to swell. Water paint, moreover, is applied in thicker and heavier coats than oil paint. In drying, the paint contracts strongly and, in doing so, exerts a considerable pull on the underlying film, weakening the grip of any parts which are not firmly attached to the surface.
A substantial strain is placed on the bond of the old coating, and this cross section vividly shows the problem – the dark line towards the top and marked with an ‘X’ is a layer of a “bound distemper”. Two, three, or even more coats can be safely applied on occasion, but there comes a time when the weight and stress are too great and cracking and flaking take place at the weakest points in the system. Local repair and making good is of no help and wholesale removal back to a sound base is the only way to tackle the problem.
Unfortunately it is not possible to lay down any rule or even give any indication of when failure is likely to take place and the appearance of the old finish is not necessarily a reliable guide to its stability. Much will depend on the quality of the old coating and the number of coats on the surface. The atmospheric conditions to which the finish has been exposed may influence its behaviour; in a room subject to a certain amount of condensation, for instance, the repeated wetting and drying of the surface will progressively weaken the binder of the water paint.
Is it worth taking the risk merely for the appeal of using a product with an esoteric or rose-tinted name on the label? Surely the decoration and protection of the building is worth more than allowing oneself to be manipulated by the marketing man?
This is the sort of information that customers of Papers and Paints can expect to be given if they seek our advice. During our fifty years of trading we have built up a considerable knowledge on this and other decorating issues. We may not be able to offer you a “lifestyle” but we can certainly help you decorate your house.
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