How to Prepare Wooden Furniture for Refinishing

Refinishing furniture isn't just a matter of removing one finish and slapping on another; it also involves preparation of the stripped wood. Preparing the wood takes both time and elbow grease, but it's vital to the success of your refinishing job; the finish is only as good as the preparation for it. In this article, we will review the three basic steps for preparing wood furniture: sanding, bleaching, and sealing. We'll beging with the first step in most home-repair projects -- sanding.

Sanding Technique

Sanding, more than any other part of refinishing, is a process that can't be rushed. It must be done by hand; power tools can damage the wood. It must be done carefully and thoroughly and always with the grain. But it's a demanding technique only in terms of time, because what it requires is chiefly patience. The care you put into sanding will determine the quality of the finish. Before you begin the work, make sure you know the basics.

The first rule of sanding is to work with the grain of the wood, because cross-grain sanding can leave permanent and very obvious scratches. The second rule is to use a sanding block, because you can't exert even sanding pressure without one.

For flat surfaces, the block should be padded; an unpadded block has no give, and grit caught under the sandpaper can scratch the wood as you work. For curved surfaces, your best bet is a thick piece of foam padding or sponge covered with sandpaper. The padding shapes itself to the curves, providing firm, even pressure.

Good sanding technique is easy to learn and apply. Using a sanding block, sand in long, light, even strokes along the grain of the wood. Don't press hard; too much pressure can cause gouging at the edge of the sanding block. Change the sandpaper as soon as it clogs or wears smooth.

To smooth the wood evenly and thoroughly, work with successively finer grades of sandpaper. The slight roughness left by the first sanding will be removed in the next sanding; the final sanding will remove the last traces of roughness. Start sanding with coarse-grit paper -- grade 3/0 for most woods or grade 4/0 for very soft woods, such as pine or poplar. Work up to grades 4/0, 5/0, and finally 6/0 sandpaper. Although finer-grit paper would theoretically produce a smoother surface, sanding with too fine a paper can clog the wood and interfere with finishing.

Sand the entire piece of furniture with each grade of sandpaper before moving on to the next grade. Between sandings, brush off or vacuum up all sanding debris, and then wipe the wood clean with a tack cloth. Dust or grit caught under the paper can scratch the wood. If there are tight corners you can't get at with sandpaper, use a very sharp scraper to very carefully smooth the wood in these. Scrapers can leave gouges or scratches, so use them only when sanding isn't possible.

Rungs, Rounds, and Spindles.

Narrow rungs, spindles, legs, and other round parts need special treatment. Hard sanding with coarse-grit paper, with or without a block, can flatten or deform round parts; only the minimum of wood should be removed. To sand round parts, cut narrow strips of fine-grit -- grades 5/0 and 6/0 -- sandpaper; don't use coarser grades at all.

Wrap a strip of sandpaper around the part, crosswise, and pull the ends back and forth to buff-sand the wood. Move up and down each round, changing your angle of sanding as you work to smooth the wood evenly. Be careful not to leave horizontal grooves in the wood at the edges of the sandpaper strips.

Carvings

Carvings, especially shallow ones, must be treated carefully. Because coarse sanding could blur the lines of the carving, use only fine-grit sandpaper, grades 5/0 and 6/0, to smooth the stripped wood; work without a sanding block. Sand lightly along the grain of the wood, pressing the paper into cutout areas with your fingertips. Sand as far down into the carving as you can, but be careful not to flatten rounded surfaces.

Crevices and Curved Edges

Sand along crevices with a strip of sandpaper creased to fit into the angle of the crevice. Sand only along the crevice, and use slow strokes; keep the pressure even.

Make sure the sandpaper doesn't slip. If you're not careful, you could damage the edges of the wood at the sides of the crevice. Sand convex curves carefully along the curve, pressing lightly with your fingers and being careful not to damage any adjoining surfaces or edges. To smooth concave curves, use a piece of dowel the same diameter as the curve. Wrap a piece of sandpaper around the dowel, and push it carefully back and forth along the curve. At the ends of the curve, be careful not to slam the dowel into any adjoining surfaces.

Veneers and Fine Patinas

If the piece of furniture you're working on is veneered, it must be treated very carefully. The usual sanding techniques could cause serious damage to the wood. The same thing is true for wood with a fine patina -- normal sanding will remove the patina. For the best results, veneers and pieces with a fine patina should be smoothed very gently.

© 2006 Publications International, Ltd. To sand a concave curve, use a piece of dowel, the same diameter as the curve, wrapped in sandpaper.

Smooth sturdy whole-surface veneers with fine-grit sandpaper, grades 5/0 and 6/0. Do not use coarser grades. On very thin veneers and wood with a patina, smoothing is best done with steel wool. The technique is essentially the same as for sanding; all you really need is patience.

Start working with No. 0 steel wool if the surface is rough, and work up to Nos. 00 and 000 for the final smoothing. If the surface is smooth, use only the finer grades of steel wool. Between grades, brush off or vacuum up all dust and steel wool debris, and then wipe the wood clean with a tack cloth.

Raising the Grain

When wood is moistened, the cells that make up the grain swell, raising the grain above the surface of the wood. Any liquid causes this reaction; even when the wood is smoothly sanded, the finish itself acts to raise the grain. To prevent the appearance of a raised grain in the finished piece of furniture, the grain should be purposely raised and then sanded down before the finish is applied after the final sanding.

The simplest grain-raiser is water. Sponge the sanded piece of furniture with cold water, soaking the wood evenly and thoroughly; then wipe off any excess. The wood must be evenly wet, with no dry spots and no puddles, or it may dry with water stains. Be especially careful not to overwet veneers; the glue that holds them may be water-soluble.

Let the wood dry completely. When it's thoroughly dry, the raised fibers of the grain will stick up stiffly above the surface. With grade 5/0 or 6/0 sandpaper, lightly smooth these raised fibers down to the surface of the wood; use No. 000 steel wool on very delicate surfaces. Be careful not to roughen the surface. Then brush off or vacuum up the sanding debris, and wipe the wood clean with a tack cloth.

Now that you've sanded your piece of furniture, you may notice -- now more than ever -- some ugly stains or discolorations. You might need to bleach the wood before you can begin refinishing it. Fortunately for you, we have detailed instructions in our next section.

How to Bleach Wood Furniture

In most cases, bleaching is essentially a first-aid measure not a routine part of refinishing. A piece of furniture should be bleached if the surface is marked by stains, black rings, or water spots; if the wood is discolored or blotchy; if the color is uneven; or if an old stain or filler is left after the finish is removed. Old filler is often a problem with oak, walnut, and mahogany. Bleaching can also be used to even the color of a piece of furniture made with two or more woods. It can lighten the darker wood to match the lighter one.

Before you use bleach on any piece of furniture, make sure the wood is suitable for bleaching. Some woods don't accept bleach well -- cherry and satinwood, for instance, should never be bleached. Some woods, such as bass, cedar, chestnut, elm, redwood, and rosewood, are very difficult to bleach, and some -- notably pine and poplar -- are so light that bleaching makes them look lifeless. Birch, maple, and walnut can be bleached, but bleaching destroys their distinctive color. And the rare woods -- mahogany, teak, and the other choice woods -- seldom benefit from bleaching. Common woods that are easy to bleach, and may benefit from it, include ash, beech, gum, and oak.

Choosing a Bleach

Not all bleaching jobs call for the same type of bleach. Depending on the problem you want to correct, you may need a very strong bleaching agent or a relatively mild one. Below are some common bleach options you might want to consider.

Laundry Bleach: This mild bleach can solve most refinishing color problems, from stain or filler not removed in stripping to ink stains and water spots. It works well for blotchy areas and for slight overall lightening, but it won't change the color of the wood drastically. Before you use a stronger bleach on any piece of furniture, try laundry bleach; it usually does the trick.

Oxalic Acid: Oxalic acid, sold in powder or crystal form, is used to remove black water marks from wood. It is also effective in restoring chemically darkened wood to its natural color. You're not likely to encounter this problem unless you have a piece of furniture commercially stripped because lye and ammonia, the chemicals that discolor wood, are not recommended for nonprofessional use. Oxalic acid must be used on the entire surface of the wood, because in most cases it also bleaches out old stain. You may have to bleach the entire piece of furniture to get an even color. Oxalic acid is more effective in lightening open-grained wood than close-grained.

Two-Part Bleaches: The two-part commercial wood bleaches are used to lighten or remove the natural color of wood. If you want a dark old piece to fit in with a roomful of blond furniture, this is the bleach to use. Two-part bleach is very strong and must be used carefully; wear rubber gloves and safety goggles. This type of bleach is also expensive. Several brands are available.

Bleaching Techniques

Whatever bleach you use, remember that the results are permanent -- you may be able to restain if you make the wood too light, but uneven bleaching is very hard to remedy. Make sure the wood is absolutely clean, and touch it as little as possible. The bleach must penetrate the wood evenly.

Before applying the bleach, test it on a scrap piece of the same wood or on a hidden part of the piece of furniture. Make sure you know exactly what the bleach will do and how fast. In general, bleaches act quickly on soft woods and slowly on hard woods.

Bleaching isn't difficult, but it does require some precautions -- bleaches are fairly strong chemicals. The stronger ones can damage skin, eyes, and lungs. Wear rubber gloves and safety goggles when working with bleach, and make sure your working area is well ventilated. Follow the bleach manufacturer's instructions exactly. If you get bleach on your skin, wash it off immediately.

Bleaching also requires careful application and removal. With any bleach, use a synthetic-bristle brush -- the chemicals will damage natural bristles. Apply the bleach along the grain of the wood, wetting the surface evenly and thoroughly; there should be no dry spots and no puddles. Let the bleach work as detailed below.

After bleaching, wipe the wood clean with a damp cloth. To remove any residue, neutralize the wood thoroughly; use an ammonia solution for oxalic acid, a borax solution for laundry bleach or two-part bleaches. Wash the bleached wood thoroughly with the appropriate neutralizer; be careful not to overwet it. Then, working quickly to prevent water damage, rinse the wood with clean water and dry it thoroughly with a soft cloth. Let the piece of furniture dry for at least two days before doing any further work on it.

Laundry Bleach

Apply laundry bleach full-strength, brushing it evenly over the entire surface. If you're removing spots or lightening discolored areas, apply bleach full-strength to those areas. Laundry bleach works quickly. After a minute or two, you should be able to see the stain fading. If you're bleaching out an old stain, wipe the bleach off with a damp cloth when the stain has lightened.

If you're spot-bleaching to remove spots or blend color areas, wait until the bleached spots are roughly the same color as the rest of the wood; then apply bleach again over the entire surface. Remove the bleach with a damp cloth when the color is even. Finally, neutralize the treated wood with a solution of 1 cup of borax dissolved in 1 quart of hot water. Neutralize, rinse with clean water, and dry it thoroughly.

Oxalic Acid

Oxalic acid is not caustic, but it is poisonous. Wear rubber gloves and safety goggles, and make sure ventilation is adequate. To prepare the acid, mix a saturated solution with warm water: 1 ounce of powder or crystals per 1 cup of warm water. Make sure you prepare enough bleach to treat the entire surface or piece of furniture.

Apply the acid solution evenly to the wood, brushing it on along the grain to cover the entire surface. On soft wood, you'll see results very quickly; on hard woods the bleaching takes longer. Let the acid work for about 20 minutes, then wipe it off with a damp cloth. If the surface isn't fully or evenly bleached, reapply the acid as necessary. On hard woods, complete bleaching may take up to an hour. Wipe the wood clean with a damp cloth, and wash it with clean water. Then neutralize it with a solution of 1 cup of household ammonia and 2 quarts of water. Rinse it again with clean water, and dry it thoroughly.

Two-Part Bleaches

Two-part bleach is easy to use, and usually works very quickly. The two components of the bleach -- labeled "1" and "2" or "A" and "B" -- are usually applied separately. Read the manufacturer's instructions and follow them exactly. The first solution is usually allowed to work for about 20 minutes before the second solution is applied.

Following the directions carefully, apply the first solution and let it work; then apply the second solution. One treatment usually bleaches the wood completely, but if the wood isn't light enough, treat it again. Wipe the bleached wood clean with a damp cloth, and then neutralize it with a solution of 1 cup of borax dissolved in 1 quart of hot water. Rinse the wood with clean water, and dry it thoroughly.

Post-Bleach Treatment

Treatment with any bleach raises the grain of the wood, even when the piece of furniture has already been thoroughly sanded. To prevent the raised grain from affecting the finish, it must be resanded to the level of the wood surface after the wood is dry.

After bleaching, let the piece of furniture dry for at least two days. Then sand the grain down lightly with grade 5/0 or 6/0 sandpaper; be careful not to roughen the surface. Because there may still be some chemical residue in the wood, wear a breathing mask and use a vacuum to remove sanding dust. Wipe the wood clean with a tack cloth.

One other complication of bleaching, especially with laundry bleach, is that the wood may be left with a whitish or grayish color. This is not serious; it indicates that the bleach has dried out the fibers of the wood surface. On hard woods, it disappears when the finish is applied. On soft woods, the gray color may be pronounced and the loose fibers obvious. To remove them, rub the wood firmly along the grain with No. 000 steel wool; rub the entire bleached area, and make sure the color is even. The grayish cast will disappear completely when the finish is applied.

Bleaching is a cosmetic touch but it can provide some surprisingly good results when used at the proper time.