Fillers and Shellac
Wooden surfaces contain innumerable microscopic openings called “pores.” Staining, since it is merely a coloring process, does not fill or close these pores. Filling the pores is commonly accomplished by the application of filler. If no filler is used, the first coat of varnish or shellac will often have a pitted appearance upon drying. This does not mean that varnish cannot be applied directly over stain, as some of the finest work is done that way.
It is merely necessary to apply two or more coats of varnish, depending upon the service conditions, interior or exterior, and to sand each one properly before the next is applied. Fillers are of two chief classes; liquid fillers and paste fillers. Liquid fillers are made of drying oil, varnish, turpentine, drier, and a filling material, which is usually finely divided silex or some other silaceous substance. Paste fillers are prepared by substantially the same formulas as liquid fillers, except that the turpentine is omitted.
The type of filler to be .used depends upon the nature of the wood. Close-grained woods, such as cypress, birch, and pine, require a liquid filler. For open-grained woods, such as oak and mahogany, the paste fillers are used. The finely grained wood for a steam room bench or a backyard sauna requires liquid filler, whereas a hot tub enclosure might require paste filler.
Both liquid and paste fillers are available in all the common wood colors, as well as natural, which may, however, be colored on the job to match the stain. It is usually desirable, of course, to use a filler which matches the stain in color as closely as possible. Sometimes, novelty finishes are achieved by using filler that differs from the stain in color.
It is most important to use good filler. Poor fillers contain cheap extenders and form too elastic an undercoat, which causes cracking or other defects in the varnish or shellac. This is especially undesirable in a piece of furniture that is used every day, such as a chair, table, bathroom vanity, or a set of bathroom cabinets.
If the filler is too heavy, thin it slightly with turpentine. In applying filler, the proper method to be followed depends upon the type of filler used. Liquid filler is applied lengthwise with the grain, allowed to dry thoroughly, and then rubbed smooth with Nos. 0 and 00 sandpaper and steel wool. Paste fillers are first thinned with turpentine to a heavy brushing consistency.
This operation must be done carefully, because the filler will not close up the pores in the wood if it is too thin, and it will not enter them if it is too thick. The paste filler is laid on with a stiff brush, rubbing it well into the pores of the wood, which are easily identifiable in heavy structures such as hot tub enclosures and tool sheds.
Unlike liquid filler, paste filler is first applied across the grain, but it is finished by rubbing smooth with the grain. Then it is allowed to set. The usual time for setting is about 15 minutes, but it is best to check the setting time of the particular filler by rubbing a small spot and noting if the filler holds in the pores of the wood. As soon as the filler has set enough, it is wiped. If the wiping is delayed, the paste-filler coat will be defective when it dries and will require a complete sanding operation, just as is required when liquid filler is used.
This is troublesome even for smaller projects, such as steam shower enclosures, bathroom vanities, and even swim spas. In the wiping operation, the excess filler is removed by the use of a piece of burlap or some excelsior, first wiping crosswise to the grain of the wood and finishing by wiping lightly in the direction of the grain. Allow as much time as necessary, at least 10 hours, for thorough drying. Then sandpaper in the direction of the grain, dust lightly, and the surface is ready for shellac or varnish.
and finishing by wiping lightly in the direction of the grain. Allow as much time as necessary, at least 10 hours, for thorough drying. Then sandpaper in the direction of the grain, dust lightly, and the surface is ready for shellac or varnish.
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