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How to Apply Filler to Wooden Furniture

Softwoods and close-grained hardwoods, such as maple and poplar, are ready to finish after staining. Open-grained hardwoods may require further treatment. Even after the surface is stained or sealed, open-grained wood still has open pores, and a finish applied over open pores may look uneven. To give it a smooth and evenly finished surface open-grained wood is usually treated with a filler after staining. In this article, we'll discuss the best ways to apply filler to your wooden furniture.

Whether you should fill the wood depends on both the wood itself and the finish you want. What is the piece of furniture made of? Bass, hemlock, maple, pine, poplar, redwood, willow, cedar, cypress, and ebony should never be filled; they can be finished immediately after staining and sealing. Ash, beech, mahogany, oak, rosewood, walnut, teak, satinwood, butternut, chestnut, elm, hickory, and lauan are open-grained; they are usually filled. Most of the other hardwoods -- such as cherry, birch, and sycamore -- are close-grained and should not be filled.

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Filling is also a matter of personal taste. Do you want a mirror-smooth finish on a formal table, or are you aiming for a more natural-looking finish on an informal piece? Filler produces a very smooth, glassy surface; if you want a more natural look, you may want to leave the pores open. This also affects the finish you plan to use. Under most finishes, open-grained woods should be filled, but if you don't want the piece of furniture to have a very smooth surface, you can finish it with a penetrating sealer, which makes filling unnecessary.

One drawback of filling is that most finishes don't bond as well to filled surfaces. In general, it's best to use a filler only when necessary, such as when a varnish, shellac, or lacquer finish will be applied over one of the open-grained woods listed above. If you're not sure the wood should be filled, don't fill it.

Choosing a Filler

Fillers are available in two forms, liquid and paste. The liquid type is not very useful; it's too thin to be effective on open-grained woods. Tinted liquid filler is sometimes used like lightening stain, to change the color of the wood. In most cases, filling should be done with paste filler, thinned as necessary to penetrate the pores of the wood. If you plan to finish the piece of furniture with lacquer, use a lacquer-base filler or let the filler dry for at least 48 hours before sealing and finishing. If you plan to use a polyurethane finish, make sure that filling is recommended and that the filler is compatible.

There are two types of paste filler. The most commonly available filler is based on cornstarch; it's available in a neutral tone and in several colors. This type of filler should be matched to the color of the wood; it dries only slightly lighter than its apparent color.

If you can't find a color to match the wood, use oil stain to mix a filler slightly darker than the wood; check the labels to make sure you can mix it. More than one application may be required with this type of filler.

The second type of paste filler is called sanding filler; it dries transparent and does not have to be matched to the wood. Sanding filler is silicate-base and requires only one application. Because it doesn't have to be color-matched, it is easier to use than cornstarch-base filler.

Once you have decided on the type of filler, you are now ready to begin your furniture restoration project. Learn the best ways to apply the filler in the next section.

©2006 Publications International Apply filler first along the grain of the wood. Then work across the grain to fill the pores completely.

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.

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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.

©2006 Publications International When the surface of the filler dulls, wipe off the excess with a coarse cloth, first across and then along the grain.

Post-Filler Treatment

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.

©Publications International, Ltd.

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