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What do you know about paint?
By Ray Lewhite.

Almost every do-it-yourself enthusiast is interested in paint and its application. But one may easily be confused by the multiplicity of types of paint which are available and by the claims made for their performance. Lacking the experts know how the amateur painter who fails to get the expected result when painting may be inclined to feel that the claims made for a certain paint have been exaggerated. In all probability, though, it is the method of application which has been at fault. Paint is not a finished product. It is a well-prepared material for doing a certain job, and there are types of paint better suited to some surfaces than others.

Different names

What do you know about paint
In this article I hope to present paints in the simplest terms. And I want if possible, to clear up some misconceptions regarding types of paint, many of which have names which differ even though the function and class grouping is the same. Paints may be defined as being mechanical mixtures of liquids and solids which, when spread out over surfaces, begin to behave in a pre-determinated chemical fashion. That is, a chemical change takes place. No matter what type of paint, all paints consist of pigments (the solid portion) and the vehicle(the liquid portion). This vehicle, aptly named as it carries the solids, may consist of several liquids. These may be a varnish constituent plus a solvent and possibly other liquid additives to impart various characteristics to the finished paint or to effect the behaviour of the paint under the brush. Protective coatings which have no pigments, and are thus clear, are known as varnishes and they consist of film-forming oils and resins similar in nature to the vehicle used in a pigmented paint.

Any finish

What do you know about paint
If one considers paints as being mechanical mixtures of pigments, solids and liquid vehicles, it is easy to see that by varying the proportions of pigment to vehicle, paint may be made to dry to any degree of sheen from dead flat to very glossy, assuming that the vehicle is itself capable of drying with a gloss. Thus a mixture consisting mainly of stiff pigment with a small proportion of oil liquid vehicle as a binder would be practically incapable of being applied by paint brush and would have to be spread with a knife. When dry, this mixture would have no "finish" and would have a dead flat appearance. This would still be the case even if the stiffish mixture were thinned out with white spirit until it could be brush applied, because the pigment to vehicle ratio would remain the same.

What do you know about paint
It will readily be seen what happens in this case if a fair amount of a good covering pigment, which is only just bound by the oil or varnish, is applied as a paint. This mixture gives hiding power but neither protection nor decoration. The extreme opposite to this type of mixture is where a very small amount of pigment is mixed with a large volume of liquid vehicle in the form of oil or varnish. This will give a paint which may be brushed quiet easily and which is coloured to whatever the desired shade may be, but which will not in itself have much hiding power. This mixture will, however, have both protective and decorative qualities. Protective because it is a varnish, and modern varnishes posses durability in themselves and do not necessarily have to rely on pigments for protective characteristics. Decorative because with the colouring effect of the pigment which has been incorporated during the mixing, there will be colour and there will also be gloss and a smooth finish because varnish flows out well under the brush.

What do you know about paint
The two examples just given form the basic idea behind two paints familiar to all who have done any painting at all. First a paint which covers well and dries flat or with a slight sheen - an undercoat - and secondly, a paint that does not normally cover quiet as well but has colour and gloss - a gloss paint. There are other names for this type of paint and these will be explained later. Two main kinds of paint have now been explained in simple terms, but of course, there are other factors which the manufacturer has to take into account when formulations are worked out. Things such as adhesion of one coat to another, compatibility of resins to oils, pigments to vehicle and other technical matters which, whilst of interest to those who are technically minded, have no bearing directly of the problems of ensuring proper preparation of a surface to be painted and the application of the paint by the right methods.

Undercoats

What do you know about paint
What has direct bearing on the matter, however, is the correct selection of a paint for a particular surface in a particular location or room of a house, suitability of a paint for exterior protective purposes or for use in a very steamy atmosphere for example. There are many paints now available which need no undercoat so far as simple hiding power is concerned. And when one coat will provide the desired finish effect then these paints are eminently suitable, especially where no drastic colour change is involved. This does not mean undercoats have lost there place in painting systems, far from it. They are needed to give build and add weight and thickness to exterior painting work, they help to reduce cost in this manner as well as helping the structure of the paint film in other ways. Undercoats also help gloss paints to dry better, especially on exterior painting work. In my opinion the minimum paint specification for the exterior woodwork of a house from which the old paint has been burned or stripped off should be a coat of primer, a coat of undercoat and two coats of finishing gloss paint. And these last coats should be applied fairly liberally and not scraped on sparingly. The rules regarding undercoats is simple. If the gloss paint which is to be used has a recommended undercoat this should be used. If the work being done requires more than one coat, and if it is for exterior painting where protection and decoration are involved, undercoat should be used.

Flat paints

What do you know about paint
Undercoats are sometimes called ground coats. But it does not follow that all paints that dry flat or with a matt or semi-matt appearance are necessarily undercoats. They may be flat oil paints, or any other name suggesting a soft sheen finish as distinct from the brightness of a gloss finish. The names vary according to manufacturers inclinations as to sales appeal. At one time flat wall paints were almost always considered unsuitable for use where atmospheric conditions were bad such as in bathrooms and kitchens. Modern paint technology has produced flat paints with considerable resistance to the effect of condensed steam and similar conditions in poorly ventilated situations, and there is no reason to suppose that one of these paints would not perform well if used for exterior paintwork.
The point being made here, however, is that it is not always safe to assume that any flat paint, no matter what it is called, can act as an undercoat for a gloss paint. In many instances the work would be quiet successful, but in the event of a premature breakdown or poor appearance it may be difficult to trace the cause of such paint failure. In any event, one would be faced with the task of doing the work again much sooner than had been anticipated. In mentioning this I must emphasise it is assumed that a gloss paint is applied over the "undercoat" fairly soon after the flat paint has been applied. It is only reasonable to consider that a clean and non-greasy flat finish would safely be re-finished with a gloss paint on interior decorative work after the lapse of some months, say when the room or surface is being done again.

Gloss and enamel

What do you know about paint
When learning geometry at school we are told that things which are equal to the same thing are equal to one another but this is by no means true of paints such as gloss paints, quick drying enamels, enamels, gloss enamels and lacquers. They all produce, given good preparation and surface, a gloss finish, but they are not all alike in performance and suitability for various purposes.
In the first place the word enamel is one which the paint trade has borrowed from the vitreous enameller, who fuses glasslike mixes and fluxes on to steel at high temperature. It has now become a term in general use where paint is discussed, and refers usually to a bright hard surface obtained by brushing or spraying a certain type of paint on a properly prepared surface. The term may be said to refer to surface hardness of the paint rather than sheen, as there are enamel and gloss paints which are matt in finish but harder than some flat wall finishes.
Generally speaking, the handyman will wish to know how to decide whether a paint described as gloss paint, gloss enamel, hard gloss enamel and so on will be suitable for exterior painting or for the use in bathrooms and kitchens. Most paint recommendations given either on tins or in literature can be relied upon, and if a paint is described as being suitable for exterior and interior work it may be safely used. What is sometimes harder to decide is whether a paint is suitable for finishing surfaces are handled such as kitchen cabinets, bathroom stools and the like. One can often decide from the sizes of the tins offered, as well as from the names and suggested uses on the tins. Most paints described as quick drying lacquers, quick air-drying enamels, 2-4 hour lacquers and enamels have very good durability even for exterior work use, but are in the main intended for the painting of smaller surface areas, and these tins are thus sold in small packs even as small as tinlets. Paints of this kind have a harder surface finish than gloss enamels and paints intended for other woodwork, such as interior and exterior doors and window frames. This hardness is achieved much quicker than one would expect from the gloss enamel type paint. Accordingly their quick drying and rapid hardening provide a means of getting a smooth fairly dust free finish on surfaces which are more important from a decorative than from a protective aspect. The drying time is given on the paint tin or in literature is also indicative of the suitability of the type for a certain job. Exterior grade gloss paints will dry in times varying from six to nine hours, but all the quick air-drying enamels have a much faster drying time than this.

What do you know about paint
Brushing cellulose lacquers are for small surface areas because cellulose has the effect of softening previous coats and it dries so rapidly that brushing over large surfaces is virtually impossible. Again these paints are sold in small tins. Thixotropic or jelly paints are a new development of an old characteristic of some paints. A paint which is rather thick and pudding-like cannot at first sight be assumed to brush out easily. But many paints will tend to become more fluid when under the action of a stick during stirring or a brush during application. The products now sold as non-drip paints are specially made so that when in the tin they are jelly-like and thick, but when being applied behave normally. When once applied they immediately become stiff once again, allowing a somewhat heavier coat to be applied without risk of runs, sags or curtains, as these defects are variously called. Some may be found to be somewhat slow in hardening as the film applied might be thicker than usual. Finally we come to the water-thinned flat or semi-gloss wall finishes known as emulsion paints. Although the older type of water paints were, strictly speaking, emulsion paints, it would be confusing not to call them this because of the extensive use and popularity of the water thinned paints made on a synthetic resin base. These are known or described as plastic emulsion paints, PVA emulsion paints, Emulsion flat finish or some other name indicating either emulsion, plastic or PVA. These initials mean polyvinyl acetate, which is the resin most commonly used in the making of these emulsion paints. It is generally agreed that for many uses PVA emulsion paints are superior to water paints as they dry immediately the water has evaporated and then can be re-coated. They have little odour during drying and rooms can be painted and used again very quickly even by those who are normally allergic as applied. Although PVA emulsion paints can be used for woodwork they are mostly used for plaster walls and for the coating of hardboard and other surfaces requiring a flat sheen finish. Emulsion paints are applied by brush or roller and it is very important to wash out the tools as soon as finished even when only breaking off for a meal, as hardened emulsion paint in brush bristles is difficult to remove.
Splashes on clothes must also be cleaned off quickly with clean water as, once hardened they cannot readily be removed even at the dry cleaners. Go Back to Home Page


Special Paint Finishes.