Applying Shellac Varnish
Tips and instructions on applying shellac to wood surfaces for varnishing.
¶ Shellac is greatly used as a liquid filler for furniture and interior trim. It is an excellent filler if used in thin coats and if sandpapered enough to remove all shellac except what has lodged in and filled the wood cells. It penetrates the pores of the wood, dries quickly enough to save much time because it permits varnishing the same day as the shellac is put on and it seals up any stain coats or filler coats which might be lifted by subsequent coats of varnish or which might bleed through the finish.
¶ While shellac is very valuable for many purposes, it is entirely unsuited for others. It will not withstand moisture without turning white. It does not make a really tough and hard surface. The orange shellac is translucent, while bleached or white shellac is transparent. Shellac gum absorbs moisture readily from the air in damp rooms and is then difficult to cut with alcohol. Gum should be stored in dry places sealed up tightly.
¶ When shellac is kept in open pots and allowed to dry hard by the evaporation of the alcohol you cannot re-dissolve the hard gum to make a good varnish, not even with alcohol. The hard gum is then worthless. Of course when it has merely thickened by such exposure.
¶ It can be thinned again with the addition of more alcohol.
¶ One or two coats of shellac on trim or furniture do not produce a really durable finish, but several coats, as in the French polishing process, with oil coats too, make one of the most durable finishes known. Pure shellac doesn't scratch nor mar; it is an elastic finish. Finishes built up with water stain, several coats of thin shellac and wax are durable and do not take on a white cloudy effect when moderately exposed to moisture, as is sometimes noted on finishes where varnish is put on over shellac.
¶ Flat and dull lustre finishes are very popular now for walls, trim and furniture. Shellac is one of the best materials to use for finishing furniture to avoid the new, shiny look and to make it fit into the color scheme better. Shellac makes a very fine finish but not a low cost job. Eight coats are needed where shellac alone is used for the finish, and a handsome as well as a durable one results. Apply two coats of pure shellac the first day six hours apart. Allow two days for drying. Then apply six more coats, allowing two days for each to dry in a well ventilated and dry room. Rub the fourth and eighth coats only.
¶ It is not wise to apply shellac over stain, not even over water stain, the same day that the stain is put on. And do not apply more than two coats of shellac in one day, except in the French polishing process where shellac is used as thin as water.
¶ Rub shellac with pumice stone and oil or with very fine sandpaper, never with pumice stone and water, or a white clouded surface will result.
¶ Orange shellac from which the natural orange color has been extracted to make white or bleached shellac sometimes proves difficult to keep in good condition. Not all of the bleaching chemicals have been extracted and the action continues. Strain white shellac often and if you find undissolved pieces of gum don't use the shellac, especially do not use it on mahogany finish as it is likely to make a cloudy white effect under the tarnish.
¶ Bleached white shellac takes on moisture and should not be used in a humid room. A hot, muggy atmosphere may give a cloudy appearance to the finish as is sometimes noted on furniture and store fixtures put into new cement buildings before the steam heat is turned on for a month or two. Humid hot climates experience considerable difficulty in this respect unless furniture and fixtures are finished especially to meet this condition. The white cloudy effect often disappears when the building becomes bone dry.
¶ The use of white bleached shellac on dark finishes, especially on mahogany is not wise. In time the shellac will cause a cloudy white film to appear under the varnish. Orange shellac is needed for such surfaces.
¶ Shellac is not suitable for any outside surfaces, not even when covered with varnish. It must not be used on damp surfaces or upon surfaces which are likely to become damp later.
¶ When using shellac to touch up bare spots on old varnish floors, use orange and white bleached in varying proportions to get the color wanted.
¶ Some finishers add a little glycerine thinned with a little alcohol to shellac to slow up its rapid setting and make it easier to brush on without showing laps and joints. Some use 10% by weight of Venice turpentine, or 1 oz. of camphor gum to one gallon of liquid shellac, for the same purpose, but the practice, while successful in accomplishing these purposes, is of doubtful merit unless used with skill and extreme caution and in wood alcohol cut shellac which sets very rapidly.
¶ Do not use shellac on surfaces which are hot.
¶ Brushes used for the application of shellac should be the largest possible for the size of the surface, this in order to make it unnecessary to use many strokes to cover the surface. For large areas a four-inch flat brush is about as large as can be handled while for smaller surface the three and two-inch varnish brushes are about right. The furniture finisher uses soft badger, ox, bear and similar brushes.
¶ Shellac must be brushed on rapidly and in one direction. Very little rebrushing can be done because shellac sets so rapidly. This material brushes "short" and cannot be stretched out like paint or varnish. Be careful not to skip places,they can only be avoided by getting the right light on the work. It is especially difficult to brush shellac dissolved in wood alcohol which causes it to set quickly, yet dry hard more slowly than grain and denatured alcohol.
¶ One gallon of shellac, cut to about 3 ½ pounds of gum to 1 gallon of alcohol, will cover about 500 square feet, one coat.
Next Page: Varnishing Wood.
This is Applying Shellac Varnish.
www.craftsman-style.info is Copyright © 2005-12 by International Styles