When liquid wood fillers were first placed on the market, they were offered as a shellac substitute, soft woods, such as white wood (poplar), white pine and spruce being more largely used in building operations and furniture than they now are. Denatured alcohol was then not in use as now, and wood alcohol shellac varnish was not much favored for interior work on account of the ill effects on the operator's eyes and lungs. Thus the advent of liquid wood filler was hailed with enthusiasm by painters, and the material at that time was composed of far better material than is the case with most of it to-day. Sharp competition on the part of the manufacturers accounts for this. All sorts of mineral bases have been tried from time to time, silica and silex, china clay, magnesium carbonate, barium carbonate, talc or soapstone and even terra alba and starch.
A good liquid wood filler that will give satisfaction, but may be found rather high in cost to meet competition in some quarters, is prepared as follows, the batch producing 50 gallons: -
12 pounds pale liquid drier; 30 pounds spirits of turpentine 308 pounds pale mixing varnish:
This will weigh 9 pounds per gallon, and if the clay has been thoroughly dried and is naturally unctuous, it should not settle hard in bottom of container. As a matter of precaution, however, one gallon of emulsion as described under Ready for Use Liquid Paints may be stirred into a batch of 50 gallons. As the quality of liquid wood filler depends to a great extent upon the quality of the varnish used in its preparation, a filler sold at low price must necessarily be made from lower priced material. For a filler of that sort the following will serve as a guide: - Grind 50 pounds asbestine powder in 30 pounds raw linseed oil, which will produce 80 pounds of soft paste, which reduce in a liquid paint mixer with 3 gallons pale liquid drier and 34 gallons pale gloss oil (rosin and benzine liquid) and 7 gallons benzine, resulting in a batch of 50 gallons weighing 7 3/4 pounds to 8 pounds per gallon, according to the body of the gloss oil.
Liquid Fillers and Stain combined are produced by simply adding to the liquid filler such colors as are described under varnish stains and in similar quantity per gallon.
Paste Wood Fillers must have the faculty of closing up the pores and interstices of more or less open grained woods in such a manner that while the surface so treated becomes non-absorbent, the natural beauty of the wood must not be obscured, and if the wood has been stained, the filler must not dull the transparency of the stain, or if the filler has been colored the filling material must not injure the richness or transparency of the color. Therefore, the more translucent the filling material the more valuable the product, and while barytes, whiting, clay and gypsum have been and are still employed for the sake of cheapness, the very best material is pure silex or silica. Starch and dextrine have also been used, especially for holding the heavier minerals in suspension, but as these perish readily under the influence of moisture, their use is not recommended. When barytes is used in paste filler it is done with a view to lessen cost of production, as barytes requires not much more than one-third the weight of vehicle required by silex, talc or clay. The latter two pigments are too unctuous, whiting is too prone to show up white under varnish and terra alba or gypsum is too short and tends to cake hard with the vehicle in the containers. As a paste filler is thinned with turpentine or benzine, mostly the latter, and applied to the surface like a flowing varnish, and the excess of filler after its setting wiped off with tow, waste or excelsior, the vehicle in which the filler is ground must be so selected that the material does not work gummy and pull out of the grain. It is obvious that a japan containing rosin will not work properly along with the oil binder, and yet a strong drier must be used, as the filler is required to dry hard enough to sandpaper in twenty-four hours. Paste filler, light or natural, must be ground in a liquid of 4 parts raw oil and 1 part good grinding japan by volume. A good figure for a batch of paste filler, natural, is as follows: - 125 pounds floated silex, 24 pounds raw linseed oil, 6 pounds medium grinding japan. When too stiff to go through the mill properly, add sufficient thin liquid drier or turpentine if not too high in cost. For colored fillers do not add colors in oil to above grinding, but use dry colors, as it will clean off the surface more readily.