Liquid Wood Fillers & Surfacers

Liquid Wood Fillers & Surfacers

How to use liquid based wood fillers and surfacers.

Craftsman Style

¶ Close-grain woods like maple and birch, and those which are halfway between these, and the large open-grain woods like oak, chestnut, ash and elm, call for a filler of a liquid rather than thick paste consistency.

¶ For example mahogany, walnut and rosewood are considered open-grain woods and yet they have not the large open cells of a size found in oak.

¶ Some finishers use paste filler thinned considerably as a liquid filler. Some use one or two coats of shellac as a liquid filler, rubbing each down to the bare wood fibre so as to remove all shellac gum except what is lodged in the pores of the wood. Others use one of the many factory-made liquid fillers which are transparent. They are sold in quart, half-gallon and gallon cans. These materials when made of first-class varnish by one of the well known manufacturers are excellent.

¶ Liquid fillers composed of gloss oil, hard oil or other cheap varnishes are not dependable materials. Some of the cheap fillers bleach out white in time and make a mottled cloudy appearance under the varnish. Some are too brittle and so crack.

¶ Shellac makes a good filler. The white bleached shellac should be used for natural and light colored finishes while the orange shellac must be used for dark colors. White and orange are mixed for finishes which are medium dark. When white shellac is used on dark mahogany or other dark finishes it sometimes gives the finish a white cloudy effect in time. Shellac should always be used thin as a filler. One or two thin coats (a 2 or 3 pound cut) are best, letting each dry and sandpapering well to remove all shellac except what is in the wood cells. Shellac does not adhere to the surface or to subsequent coats of varnish any too well and for that reason a complete film of shellac makes a poor foundation. When used to fill the pores or cells only, however, it is excellent. Shellac, also acts as a sealer over oil stains, preventing the oil from affiliating with the varnish. Varnish in direct contact with oil sometimes remains soft and tacky for a long time. The shellac coats over aniline stains, especially over reds in the oil or water form often prevents these stains from bleeding.

¶ A formula for liquid filler used by some finishers is as follows:

1 gallon of pale cabinet varnish, or better yet, use the same kind of varnish as you will use for the varnish undercoats. Then it unites better and there is less danger of cracking.
1 quart turpentine.
1 pint japan drier of light color.
2 ½ pounds dry bolted china clay or water-floated silica.
Mix the clay or silica well with a little of the varnish. Then the other liquids are added and thoroughly mixed. Grind the whole batch through a paint mill if one is at hand. It can be mixed with a paddle, however. After thoroughly mixing let the mixture stand two or three days and strain through muslin. Thin to easy brushing consistency with benzine or turpentine. Stir the filler occasionally while using to keep the silica in suspension; it may settle to the bottom. A little more or less silica or clay may be needed, depending upon the kind of wood. It should dry flat, but not dead flat, Use less pigment to avoid the dead flat. When correctly mixed this filler will sandpaper as easily and as clean and smooth as shellac, making a level, well-filled surface.

¶ Brush this filler on in a thin coat as a rule. A heavy coat may safely be used if the filler is well distributed but you cannot wipe off a thick liquid filler coat and it will, therefore, reduce the transparency of the finish. That is all right on cheap work. Apply the filler with as little brushing as possible after distributing it evenly. Let the coating dry hard, preferably over night or longer, and sandpaper it smooth with No. ½ paper, removing all filler except that which remains in the pores of the wood. Trying to save time by cutting short the drying of any kind of filler is poor economy. Wet or immature filler slows up the drying of varnish coats and may cause worse trouble than that.

¶ After brushing on a thin liquid filler allow it to set a few minutes and then wipe off all filler not lodged in the wood cells and cracks. If not wiped off clean it will bleach out white in time and show white clouds or a muddy appearance under the varnish. This is especially true if too much pigment has been mixed in with the filler liquids.

¶ Liquid filler is used to stop the suction of the wood? principally, and is not good for woods having large open pores. Some liquid fillers are made to be brushed on and not to be wiped clean, but when any pigment is used in a liquid filler it is safer to wipe off all except what is lodged in the wood grain, otherwise the final finish may not be as clear and transparent as it should be. Liquid fillers are used by some on oak and other open-grain wood after a paste filler to make a more perfect surface.

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