VARNISHES are quite as numerous and. As varied in character as paints. Each is designed for a definite purpose and should not be expected to prove equally efficient when used otherwise. Spirit varnishes are hard drying, almost to the point of brittleness. Oil varnishes are sometimes sufficiently elastic to permit application over oil paint, while other types are designed especially for use upon floors, wallpapers, baths, boats, and almost every conceivable kind of material.
Oil varnishes constitute the most important class, and may, for con-venience, be divided into two groups, the hard-drying varnishes (for interior work only), and the elastic varnishes, which contain a higher oil content and tougher resins, to enable them to withstand exposure,to varying weather conditions. A general purpose varnish, which is claimed to fulfil both sets of conditions, can hardly succeed in meeting such widely different demands.
Synthetic varnishes are becoming increasingly popular for outdoor use, their quick-setting characteristics causing the surface to harden and become dust-proof, and often weather-proof, in two or three hours. In these, the linseed oil is combined with an artificial resin, frequently of the bakelite type, and the resulting product when applied to a surface will withstand a considerable amount of washing down without injury.
Flat, I.e. non-glossy, and eggshell flat, I.e. semi-glossy, varnishes are intended for use upon an undercoat of gloss varnish, while others can be applied directly upon flat oil paint to improve and protect the surface. Such varnishes are quite unsuitable for outdoor work.
Spirit varnishes are simple solutions of shellac, wood resin, or other easily dissolved resins, in a suitable solvent such as industrial alcohol, naphtha, white spirit, etc. French polish is probably the best known type of spirit varnish, and the same conditions of warmth and dryness are equally essential during the application of all such spirit preparations.
Their suitability is strictly limited to indoor use upon new or stained woodwork, but not upon floors or painted surfaces. Articles of furniture, and shop or office fittings, offer a wide scope for these hard quick-drying, brush-applied varnishes.
Japanner’s gold-size in an oil varnish combining a drying agent, but it possesses neither resistance to weather nor outstanding gloss. Its value lies in its capacity of drying within an hour, thus enabling it to be employed as a mixing varnish, or as a sealing coat prior to the application of a more expensive oil varnish upon anti-drying surfaces, such as new teak and Columbian pine.
Varnishes, specially manufactured for application on paper, meet the demand for an extra pale and durable oil varnish suitable for use upon sanitary or other wallpapers which are capable of withstanding the preliminary coats of glue size. Its resistance to water and steam makes it ideal as a protective coating in kitchens, bathrooms, and humid situations generally.
Surfaces for Varnishing
It may appear from the list of varnishes mentioned, that anything and everything can be successfully coated with the appropriate lustrous finish. But it is not only important to choose the right material for a job; there are other factors to be considered of equal or greater consequence.
Surfaces must be hard and firm, quite free from dirt and grease, they must present a smooth, non-porous surface, must above all, be absolutely dry, and, if possible, of a non-glossy character. Few surfaces comply with these exacting conditions, but good preparation must always aim at their production. A durable and satisfactory finish can never be obtained otherwise. Cracks, crevices and holes should be filled with plaster of Paris, putty or quick-setting proprietary cement, as, the stopping being stained later to match, if necessary.
Absolute cleanliness is of major importance. The floor of the room should have been swept or washed, and the dust allowed to settle before attempting any varnishing in it. Varnish brushes must be clean and dry, and the vessels used for the varnish must be equally clean.
Painted surfaces should be of an egg-shell gloss (semi-flat) type, and be wiped down with a clean, damp wash-leather to remove dust. Outdoor work will obviously have to be postponed if rain, mist, frost, or dusty conditions prevail.
A warm temperature of between 60 degrees and 70 degrees Fahrenheit is a decided asset during the application of oil varnishes but this is not so important as the avoidance of a sudden fall in temperature during the early stages of drying. For this reason it is preferable to complete all varnishing during the morning, so as to have the work almost dry before nightfall. Newly applied varnish may also be chilled by undue exposure to draughts, the result of chilling being similar vto that produced by varnishing upon damp surfaces, and manifesting itself by loss of gloss or by a whitish surface bloom.
Varnishing Painted Work
Choose an oil varnish of a hard drying or elastic type according to the location of the work (I.e. whether inside or outside) and secondly, use the palest varnish available if the paint is of a delicate tint. No varnish is absolutely colourless, but some, particularly the dark oak varnishes, are suitable for.use only upon dark or medium coloured backgrounds.
Varnishing requires a different technique from painting. The latter is applied sparingly and is finished with the lightest possible brush strokes, but varnish must be applied liberally and with enough force to spread the coating evenly. The work is then crossed and laid off as in painting but the toughness of the material demands slow, firm, brushwork throughout. Work up well into the corners of panels, mouldings, etc., using the brush.
The colour will be a good indicator of the evenness of the coating; if this is patchy, it will again be necessary to cross and lay off with the brush, taking care to complete each section of the work before the varnish begins to set. Two or three minutes is ample time for the varnishing of a door panel, and five minutes is about the maximum; otherwise, there is the possibility of brush marks failing to level out.
Each door or wall should be completed one section at a time, always joining up before the previous section has commenced to set. Pay particular attention to mouldings, for it is here that excessive coating may occur, which, if not removed with the brush, may crinkle or run.
After completing a door, it is wise to examine the job several times at ten minute intervals, to make sure that any runs are immediately noticed and levelled out with the semi-dry brush. It may be found (especially where turpentine substitute has been used in undercoats) that bare patches have made their appearance. These must be treated in the same way as runs, repeating several times if necessary.
Bare patches are a common trouble during the application of both varnishes and gloss paints. Such cases indicate a slight greasi-ness of surface which is easily cured by rubbing the unvarnished paintwork with a damp sponge (or wash leather) sprinkled with fullers earth.
Varnishing New Woodwork
Hardwoods should first be stopped, sandpapered, stained (if required), and the grain filled . The first coat of varnish or gold-size should then be applied rather sparingly and allowed to harden for forty-eight hours. The surface is then rubbed down lightly with fine waterproof sandpaper, using water as a lubricant, and the work dried off with the leather. Apply a finishing coat of varnish when the surface is sufficiently dry.
Teak, Columbian, and Oregon pine are stopped, sandpapered, and then given a sealing coat composed of two parts japanner’s gold-size to one part turpentine. The surface is then safe for either staining or varnishing.
Softwoods usually present surfaces of such uneven porosity that the application of stain or varnish immediately accentuates the fact by a marked difference in tone and colour. This patchiness can be greatly minimized if the work is given a preliminary coat of french polish or white knotting prior to staining or varnishing. For work of secondary importance, a coat of jellied glue-size will answer the purpose.
Staining and Varnishing Floors
A stained and varnished floor margin makes an ideal surround for carpets and at the same time is more hygienic and economical than linoleum. If an oil stain and floor varnish are employed, the job will last for five to ten years without deterioration, providing that the surface receives an occasional dressing of floor polish. Varnish stains dry quickly and do not penetrate deeply, with the result that they are more easily marked.
Floorboards should be scrubbed clean and allowed to dry before stopping the nailholes with plastic wood. The oil stain consists of equal parts linseed oil and turpentine tinted with burnt umber and raw sienna; to this must be added about ten per cent liquid driers. One pint will cover approximately fifteen square yards when applied with a brush.
The stain and varnish must each be allowed twenty-four hours for drying and hardening off after application. Two coats of varnish will be necessary, the amount required being calculated on the basis that one pint covers eight square yards of surface.
There are two important essentials connected with papering and varnishing which, if neglected, will spoil the job. In the first place, it is obviously necessary to see that all joints and edges of the wallpaper are firmly attached to the wall; a point demanding special care during both the preparation for and hanging of the paper. All cracks between walls and skirtings or architraves must have been properly filled with plaster, otherwise varnish may creep behind the paper and cause discoloration. The second essential is the application of two coats of weak glue-size (brush applied), which serve as an efficient protection against the staining action of oil varnish.