Prior to 1914, the highest class of paint finish was obtained by the use of a long-oil enamel. Such materials are still made and of first-class quality, but the art of enamelling, as it was once understood, is more or less obsolete, and the reasons are not difficult to understand. It involved considerable expenditure of time in the initial preparation of the surface, the application of half a dozen coats or more, with ample intervals for drying and rubbing down between each coat, the progressive building-up of a finish which, at its best, was not only remarkably durable but had and maintained a high degree of gloss and a certain depth and richness unobtainable by any other means. Some of the old-style enamel work still survives in good condition in older houses in various parts of the country, and it is obvious that only skilled craftsmanship could have produced it.
It must be remembered, too, that this type of finish owed its popularity not only to the fact that, when it was in great demand, the cost of labour and materials was relatively low and time was of no great account, but also to the fact that the only alternative glossy finish was oil paint which, whatever its other virtures, was substantially inferior so far as gloss was concerned. Not many people to-day would be willing to pay for, or put up with the delay necessary for the coat of primer, two or three filler coats, and three or four undercoats, each carefully applied and flatted, which would once have been considered no more than an adequate foundation for a first-class enamel job. But nowadays, in addition to the oil-gloss finish, we have the enamel paint type, and hard-gloss finishes, the better grades of which have something in common with the old enamels, though most of them dry and harden more rapidly. That their effective life is generally rather shorter than that of the older form of finish is mainly due to the fact that far less time is spent on preliminary work and far fewer coats are applied.
A high-grade white enamel is usually made on a zinc-oxide or titanium-oxide base with a varnish or specially treated oil medium. Extreme fineness of grinding and great experience in mixing are essential in its production. It should have a high degree of gloss and retain it over a reasonably long period, exceptional whiteness, and good, self-levelling properties. The age is now gone when rapidity of drying was looked upon with suspicion by the decorator and, though certain types of slow-drying enamel are still made, the majority of enamels are none the less reliable because they dry and harden in a comparatively short time.
Good results in the use of enamel still depend largely on the care with which the surface is prepared, for although the property of self-levelling, which is one of its most important characteristics, eliminates all traces of the passage of the brush and thus helps to produce a higher gloss, it is not entirely an unmixed advantage; it causes the material to follow the contours of the surface more closely, and consequently to exaggerate rather than to conceal any minor defects in the groundwork. An oil paint, which lacks the property of flowing out, is less likely to behave in this way, if applied by a skilled brush-hand; it tends to adjust itself better to any irregularities of the surface while the slight texture imparted to the film by the action of the brush helps to mask them. While the greatest possible care in the preliminary work and in building up the finish is desirable with both types of finish, it is the enamel which is the more likely to reveal any shortcomings in this respect.
Enamel Paint, Hard-gloss Paint
As already pointed out earlier in this work, the rather indiscriminate way in which such descriptions as ‘ enamel,’ ‘ enamel paint,’ and ‘ hard-gloss paint’ are applied to products makes it difficult, if not impossible, to draw any hard-and-fast distinction between them. The difference is not necessarily one of quality, for a few high-grade finishes, sold as ‘ hard- ‘ or ‘ high-gloss paints,’ seem to be little inferior in appearance and performance to some which are marketed as ‘ enamels,’ although it is generally understood that the latter should be of a better grade.
It may be permissible, therefore, to classify present-day gloss finishes under two main heads – oil-gloss paints and enamel-type paints. The first of these may be defined as paints in which linseed oil, either raw or boiled, is used to produce the gloss. By enamel-type paints, on the other hand, is meant those in which the vehicle consists of specially processed oils – not necessarily linseed – or of varnishes, or of admixtures of both. The chief difference between the two, from the painter’s point of view, lies in the degree of initial gloss produced, and also in the fact that the enamel type possesses a certain amount of flow – varying according to the formulation – whereas the oil-gloss type has none. This involves a substantial difference in the technique of application of the two varieties, and it is important that this should be realised.
Gloss Oil Paint: Notes on the application of this type of paint have already been given earlier on in this post . In general, its consistency should be ‘ round ‘ enough to ensure that the material will not run unduly after it has been transferred from the kettle to the surface. Too much should not be taken up by the brush and the aim should be to distribute the paint as evenly as possible, avoiding runs and ‘ fat ‘ edges. It should then be crossed, spread farther by vertical strokes, crossed again and finally laid off, the pressure decreasing progressively until, at the end of the operation, it amounts to no more than the merest touch which smooths away the brush marks.
In applying finishes of this kind, the rule should be to flow it on evenly and let it alone. It should be brushed out only sufficiently to provide a coat of the correct thickness, after which its inherent property of’ flow ‘ will cause any brush marks to disappear. If any are left when the film dries, it is because the brushing has been continued too long after the coating has taken on its initial set. The period which elapses before this set takes place will vary according to the formulation of the paint and the temperature in which the work is carried out.
Under this heading, it will be sufficient to consider four main classes – flat enamels, flatting, egg-shell flat finishes, and flat wall paints.
This type of finish requires little description. As a rule, it is made with pigments which are highly absorptive, with a special oil and varnish binder, and dries fairly rapidly to a hard mat surface. As is the case with flat wall finishes, flat enamels are an exception to the ordinary rules of coat sequence, in that they are applied over a flat ground.
Formulations differ to a considerable extent, according to the manufacturer, but some brands of flat enamels demand a good deal of skill in manipulation if the best results are to be obtained, as, if worked too long under the brush or when joining up large areas, they are liable to ‘ flash.’
Flatting is paint which dries with a more or less complete absence of lustre, although, it should be added, an absolutely ‘ dead ‘ flat is far from easy to obtain. The lack of gloss is obtained by cutting down the oil content to a minimum and by having a large preponderance of turpentine over oil in the liquid portion of the paint. A finish of this kind, if applied over an ordinary hard, dry ground, would not last very long, because being underbound, it would have little adhesion. True flatting must consequently be used only over an oily ground coat, before the latter has had time to harden properly and, in fact, while it still possesses some degree of tackiness.
As a general rule, paste white lead is employed for making up flatting, because it absorbs comparatively little oil in grinding – on an average, about 8 per cent. This is just sufficient to bind it without imparting more than a very slight degree of gloss to the finish. The main objection to the use of white lead in this connection is its tendency to discolour in the absence of sufficient vehicle to encase and protect the pigment.
Zinc oxide needs more than twice the amount of oil in grinding as compared with white lead, and a paint made up from zinc oxide in oil will give a film too lustrous to be considered a true flatting. If it is desired to use this pigment, it will therefore be necessary to add at least an equal amount of zinc oxide in turpentine, with a little extraneous binder. This will give a brilliantly white, flat finish.
Flatting must be carefully mixed and strained and it is best to prepare it overnight and allow it to stand at least twelve hours before it is put on. If a tinted finish is wanted, stainers ground in turpentine should be used since stainers in oil may impart rather too much gloss. The consistency should be sufficiently thin to permit rapid application and care must be taken to keep the edges ‘ alive.3’ On large flank walls, two or even three men may be necessary. The whole of the surface must be evenly covered, section by section, and then stippled to ensure absolute uniformity and freedom from brush marks or flashing.
Although this cannot be regarded as an exact description, it gives a very fair idea of the degree of gloss which it commonly implies. It is usually made up from the same kind of ingredients as true flatting, but contains a rather higher proportion of binding material; the latter should be in the form of a good, pale varnish rather than in that of additional oil.
The ground over which egg-shell flatting is applied should be less oily than that employed for ordinary flatting and should be allowed to dry hard.
Flat Wall Finishes
The modern flat wall finish is a comparatively recent innovation and one which is deservedly popular. It is made from ordinary pigments, but research and experiments have evolved a special type of binder which, while it contains as high a percentage of non-volatile oils and gums as the average gloss-paint medium, will nevertheless dry out almost dead flat. The more progressive manufacturers have long realised that turpentine used by itself evaporates too rapidly – especially in warm weather or on outside work – to be considered an ideal thinner for flat paints or enamels, and consequently in nearly all the better types of flat finish now obtainable the turpentine content is partly replaced by equally pure but heavier diluents, and these, in conjunction with special retardant substances, slow down the rate of drying sufficiently to allow the paint to be spread properly over large areas, without showing brush marks or ‘ flashes ‘ when joining up one section with another.
If a flat wall finish, with which the decorator is not familiar, is to be employed to any considerable extent, it is a wise plan to make a preliminary test of its working properties, and this may be done, quite simply, by taking a large panel with a good, non-absorbent surface, coating it with the paint, and allowing it to dry in a vertical position for about ten minutes to a quarter of an hour. Then charge the brush and draw it gently but firmly across the panel, in the same direction as the previous laying-off; when this is dry, there should be no appreciable difference between this stripe and the first finish; the test will provide a suitable substitute for the conditions found in actual working practice, and give an indication as to the suitability or otherwise of the paint for application over large areas.
It is not unusual to find painters, when a flat wall paint shows a tendency to set too rapidly, using paraffin to make it more workable. This is a thoroughly bad practice, which should not be indulged in, in the first place, because nothing should be added to a proprietary brand of paint which is not expressly permitted by the manufacturer’s instructions as stated on the container, and, in the second, because ordinary paraffin contains a substantial amount of heavy-oil impurities which are liable to soften the paint film and impair the adhesion, not only of the material itself, but of underlying coats on which it is applied.
It is an old and elementary rule in painting that a flat coat should only be applied on top of a glossy coat and vice versa, but in the case of the modern variety of flat oil or wall paints, this need not be interpreted too literally. True, it would be unwise to give a chalky, underbound surface a coat of flat wall finish, but the latter can be safely applied on top of a paint which has only sufficient binder to give a faint egg-shell gloss. The essential point is that the porosity of the surface is adequately sealed with suitable primer, and that there is no unequal degree of absorption.
It is safe to say that the majority of defects which occur in flat wall paints are due to an uneven degree of porosity in the ground to which they are applied, rather than to any shortcomings in the material or to the manner in which it is put on. For this reason, it is most important, when painting bare plaster or woodwork, to give a thin coat of well-bound primer, so that any variations in the trowelling or in the grain of the wood can be levelled up. If the surface is unusually absorptive or ‘ hungry,’ a priming coat of a thin solution of shellac is decidedly useful.
Brushes for Flat Wall Paints
The factor which has contributed most to the popularity of flat wall finishes is, as we have remarked, the speed at which they can be applied. They possess certain flowing properties, and thus do not require to be finely laid on, so that, instead of the ordinary pound or the usual 3-in. flat brush employed for gloss paints, a brush up to 6 in. in width can be successfully used with them.
A brush with stiff, coarse bristles should be avoided, and one with fine but springy bristles is to be preferred. A good-quality flat distemper brush is used by many experienced craftsmen, and is excellent when large areas have to be covered.
Avoiding Brush Marks
While a poor-quality brush with too few or too many bristles will cause unsightly brush marks, they may also result from an incorrect method of application, and in this connection the following remarks, which were published in a U.S. trade journal, The American Painter and Decorator, some years ago, are of interest: ‘ An understanding of the theory and formulation of flat wall paints suggests the proper method of application. In the first place, flat wall paints are designed to have a very high concentration of pigment; that is, as much pigment is crowded into a gallon of liquid as possible; they are still intended to retain the liquid qualities required for brush application. Then the character of the liquid used is one to promote flowing of the paint after application. It is this flowing that will eliminate brush marks, if given a chance. Two conditions will prevent this flowing action – use of the paint on a surface that has too much suction … or brushing the paint out too much. An excessively porous surface absorbs the liquid in the flat wall paint before it has a chance to flow out sufficiently to eliminate the brush marks. Too thin a paint, caused by too much brushing, in a desire to cover too much surface with a gallon of paint, simply spreads such a thin film of paint that it cannot fill up the old brush marks in the surface, for there is not sufficient body of paint to flow out and level up the new paint. ‘ The principle followed in the formulation of flat wall paints is that sufficient pigment should be put in the paint to make a film that will completely hide the surface in one coat. In order to do the job in one coat, the paint must be flowed on freely, and, further, it should be brushed just as little as possible. Too much brushing brings the liquid to the top and makes a gloss spot. Just load the brush, apply it to a square foot or so of the surface, lay it off, and let it alone. When joining up the next brush-ful and the stretches, get along with as little brushing as you can.’
Stippling Flat Wall Paints
Stippling serves useful purposes – the elimination of brush marks and the levelling up of joins when one section of the work is picked up from another already executed. With flat wall finishes, however, it is often a matter of some difficulty for one man to accomplish it successfully, owing to the thickness of the coating and the comparatively strong degree of tackiness which it must acquire before the whole of any large area can be covered. On relatively small surfaces, it is simple enough, but on those of large dimensions it is best carried out by another man with a stippler following up behind the brush hand as rapidly as possible.
If it is impracticable to employ more than one man the problem may to a certain extent be solved by providing a shallow tray containing a layer of turpentine. The stippler should be lightly dipped in this from time to time, and any excess of turpentine ‘ pounced ‘ out of it. Any heavy layers at the junction of sections can be levelled out more effectively in this manner than if a perfectly dry stippler were used. The stippler should be cleansed at intervals to prevent undue clogging with paint.
Removing the Smell of Paint
The smell of oil paint is very objectionable to many householders, and it is therefore highly desirable to get rid of it with as little delay as possible. Various remedies have been suggested from time to time; it is claimed, for instance, that pails of water – or, better still, milk – placed in a newly-painted room will quickly absorb the smell, or again, that a liberal quantity of fresh hay, steeped in water, will fulfil the same purpose. The effectiveness of such measures, however, seems – to say the least – problematical.
The best means of minimising the smell is undoubtedly to ensure adequate ventilation by keeping doors and windows open while the work is in progress. By raising the temperature of the room, moreover, the volatile constituents in the paint can be dispersed more rapidly, and a fire or radiator, started as soon as the last coat is touch-dry, is to be recommended when practicable.