Filler usually produces a very smooth, glassy surface when applied after sanding or other parts of the refinishing process. But when you should apply filler depends on what type of surface you are working with and what you want to accomplish.
Stained surfaces should be sealed after staining to prevent bleeding; they need no further treatment before filling. Unstained surfaces must also be sealed; apply a coat of thinned shellac, sanding sealer, or other appropriate sealer. If you plan to finish the piece with polyurethane, make sure the sealer and the filler are compatible. Let the sealed wood dry completely, then sand the surface very lightly with fine-grit sandpaper. Remove the sanding debris with a tack cloth, and apply the filler.
To use paste filler, thin the paste as directed with turpentine, working it to a smooth, creamy batter. Wood with very large open pores requires a thicker consistency than wood with smaller pores. Apply the filler with a clean brush, working it firmly into the pores along the grain of the wood; then work it in across the grain. On large surfaces, fill one area at a time to cover the entire surface evenly.
Let the filler set for about 15 minutes, or as directed by the manufacturer, until the surface of the filler is dull. Then firmly wipe off the excess filler, across the grain of the wood, with a coarse towel or a piece of burlap. You want to remove the filler from the surface of the wood but leave it in the pores; you may have to experiment with the drying time to find the right timing. After wiping off the excess filler, wipe the wood slowly and carefully with a clean cloth, in the direction of the grain. Let the filled wood dry for at least 24 hours.
The filled wood should look clean. If you can see a dull haze on the surface, the excess filler was not completely removed. This haze must be sanded off to prevent clouding in the finish. Sand the hazy areas very lightly with fine-grit sandpaper, being careful not to remove either the filler in the pores or stain. Remove sanding debris with a tack cloth, and let the piece of furniture dry for at least 24 hours.
To prevent the filler from bleeding through the finish before you bond the finish to the filler, seal the filled surface before finishing with the appropriate sealer. Apply a coat of thinned shellac, sanding sealer, or other appropriate sealer. If you plan to finish the piece with polyurethane, make sure the sealer is compatible. Some polyurethanes may not require sealing over some fillers. If you plan to finish the piece with penetrating resin sealer, sealing is not necessary. Let the sealed wood dry completely; then sand the surface very lightly with fine-grit sandpaper. Remove the sanding debris with a tack cloth, and apply the finish.
Using filler will allow you to customize your furniture to your own taste.
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