Varnishes are 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 for other purposes.
But regardless of the type
of varnish, whether it is spar varnish for exterior work, floor varnish,
or varnish suitable for furniture, certain conditions must be observed
if the work is to be completely satisfactory.
Few surfaces comply with these exacting conditions but they can be achieved by a little extra work. Cracks and holes should be filled with putty and stained to match the colour of the wood. Cleanliness is of major importance in varnishing. The floor of the room should be swept or washed and the dust allowed to settle before varnishing. This applies not only when woodwork in a room is being varnished but even when a piece of furniture is to be refinished.
Certain weather conditions must also be considered if the varnish is to dry properly. No outdoor work can be done immediately after a rain, or when the air is particularly humid. Do outside work late in the morning, after the dew has had ample time to evaporate. In like manner, do not try to varnish in the late afternoon when the dew has begun to collect.
Seventy degrees Fahrenheit is a good temperature for both outside and inside work. If the temperature is too high, the varnish will dry too quickly and the quality of the finish will be poor; if too low, the varnish will not dry well. Sudden changes in temperature also affect varnish adversely.
Varnishing requires a technique different from that used for painting. Paint is applied sparingly and is finished off with light brush strokes. Varnish, on the other hand, must be flowed on with a full brush and enough force applied to spread the coat evenly. Brush varnish just enough to make a uniformly thin coat. If brushed too much, it will not spread and will leave brush marks on the surface.
Apply the varnish across the grain and finish with light, lengthwise strokes. Runs and sags in varnish must be caught before the varnish sets. Complete each door or window frame one section at a time, joining the new section before the previous section begins to set. Pay particular attention to moulding, for it is here that excessive coating may occur and cause a run if not removed with the brush.
Additional coats of varnish can be applied after the previous coat has dried and the surface sanded down with No. 00 sandpaper to remove the gloss. It is not a good plan to put one kind of varnish over a different kind, as the variation in elasticity may cause cracking. Use at least two coats of spar varnish on exterior work. New varnish can be applied to old varnish, provided that the surface is not too thick and it is sanded down with No. 00 sandpaper before putting on the new coat.
Varnish over paint
Varnish can be applied to a painted surface, but it should be of a hard-drying, elastic type.
Paint over varnish
Paint and enamel can be applied over a varnish base. Sand the varnish lightly to remove the gloss and thin the first coat of paint with a small amount of varnish so that it will be elastic and not crack easily.
Wallpaper. Varnish can be applied over wallpaper, but two essentials must be observed if the job is to turn out well. In the first place, it is necessary to see that all joints of the wallpaper are firmly attached to the wall. All cracks between the walls, in the baseboard and window frames, must be filled, or varnish may get behind the paper and cause discoloration. Second, apply two coats of weak glue size as a protection against the staining action of the varnish.