Varnish gives floors a hard, smooth, glossy finish, and is easy to apply and to clean. Under hard usage, however, it is likely to wear off, leaving patches of bare wood that remain unsightly even after revarnishing. Successive coats tend to darken the floor. Varnish is a common finish for softwood floors, but wax is preferred by many for hardwood.
Manufacturers have tested and put on the market an assortment of varnishes adapted to special uses, and it is often better to buy one of these ready-made standard floor varnishes than to attempt to mix one at home.
Varnishes are roughly classified into two groups, spirit and oil. The spirit varnishes are made by dissolving a resinous substance, such as gum shellac, in alcohol or some other volatile liquid. They dry quickly, leaving a hard, brittle coating on the wood, and, with the exception of shellac varnish, are not commonly used on floors.
Successive coats of shellac varnish well rubbed down may be used alone on a floor, or one coat may be used as a surfacer on a paste-filled hardwood floor that is to be waxed. For the first coat, 1 gallon of shellac will cover 300 to 400 square feet of floor, and additional coats will of course require less. Parquetry floors are generally shellacked in order to preserve the light color of the wood.
The oil varnishes contain resinous gum, oil, and driers, carefully heated and blended so as to bring out certain properties. Most of the floor varnishes are of this type and of the kind known in trade as "medium oil." They dry more slowly than the spirit varnishes, but have luster, hardness, and greater durability. Spar varnishes belong to the kind known as "long-oil" and contain an even larger proportion of oil, which makes them more durable and impervious to water. They are sometimes used on kitchen and bathroom floors, where those characteristics are of particular importance.
The first rule of varnishing is to have the surface of the wood and the air in the room as free from dust as possible and to use only scrupulously clean brushes. Varnish brushes are chisel shaped or slightly tapering; a rather wide one will be most convenient for this work. The varnish should be brushed on lengthwise of the grain in a smooth, thin coat without laps or brush marks and allowed to dry for at least two days. If possible, the temperature of the room should be 700 F. or higher and the varnish should be applied in the morning, for it dries better during daylight. When the first coat is thoroughly dry another coat or perhaps several more coats should be applied in the same way as the first. The more coats of varnish put on a floor, the more durable the finish. One gallon of floor varnish is enough for two coats on about 300 square feet of oak floor or about 200 square feet of pine.