Wood Finishing,
Wood Bleach

If you’re planning to apply stain to interior or exterior wood, it’s essential to prep the surface. After you’ve stripped the old finish and sanded it to 220 grit, applying wood bleach and wood conditioner can give you a truly professional look.

Bleaching lightens the color of wood and reduces both the contrast of the grain lines and the contrast between sapwood and heartwood. It can be used to remove stains or dye from previous finishes. It can help you match old, sun-faded wood or even out the colors of different pieces. You can also use bleach to help you create special effects.

Peroxide bleaches are supplied as ‘A’ and ‘B’ components that work together. ‘A’ is a caustic solution, usually sodium hydroxide (lye), which enhances the action of ‘B,’ a hydrogen peroxide solution. Some manufacturers recommend mixing ‘A’ and ‘B,’ whereas others instruct you to apply them ten minutes apart. If the bleaching effect is uneven, you can re-treat all or part of the surface. When you’re satisfied with the look, wash the surface with a solution of one part white vinegar to two parts water to neutralize the alkaline bleach residue.

Chlorine bleach is a solution of calcium or sodium hypochlorite, just like laundry bleach. Its forte is removing dye stains, as from food spills or previous finishes. It shouldn’t be your first resort for bleaching wood, as it tends to break down the lignin that holds wood cells together, producing a fuzzy, lifeless surface. If you must use chlorine bleach, don’t use laundry bleach, which is not strong enough. Make a stronger solution of bleach by buying calcium hypochlorite powder at a swimming pool supplier and adding it to hot tap water until no more will dissolve (wear gloves and goggles, wear a dust mask when you’re pouring the powder, and ventilate).

Oxalic acid, the active ingredient in products marketed as deck brighteners, is particularly suited for removing water or iron stains that turn outdoor wood black. It also removes the gray tone of weathered wood. In contrast to A/B bleaches, it leaves an acid surface that must be neutralized with a solution made from one quart of water and two heaping tablespoons of baking soda, followed by a thorough rinsing with water.

If the stains you’re removing are related to water and weather, try oxalic acid first; it is the gentlest on the wood. Otherwise a peroxide bleach will probably do the job without fuzzing the wood excessively. Save chlorine bleach for dye stains or as a last resort if nothing else works.

Bleach can make one wood look like another. For example, you can bleach inexpensive alder paneling, which has dark grain lines, to mimic the look of expensive white birch, which doesn’t. Or, previously installed paneling can be stripped of an oppressively dark finish, bleached, and refinished in a lighter color. Bob Hoppe, of the painting firm Hoppe Brothers & Sons and the decorative painting school Faux Masters, says that many people in his area (Yorba Linda, Calif.) want paneling or trim to match a set of furniture — and bleached finishes are popular with furniture makers. “For upper-end clientele, we bleach a lot of walnut,” he says. “It is in vogue. Walnut is very dark, but people like the pattern of the grain. We also bleach a lot of mahogany. They like the look, but they don’t like the red or the orange.” Fashions change, but bleaching marches on: “Back in the ‘80s, oak was very popular, and we bleached a lot of red oak to make it look like white oak.”

Hoppe’s clients provide samples of the wood in question, and he makes sample boards to determine how much bleach and how many coats of stain to use. “My favorite is Klean-Strip 2-part wood bleach [from W.M. Barr],” he says. Hoppe applies the bleach sparingly, with a sponge or a stain pad, wiping off any puddles or drips, which will stain the wood. When the wood is dry, he applies another coat until the color is right — one or two coats for oak or pine, or as many as four for mahogany or walnut.

When bleaching veneer, don’t get the surface too wet. “Any time we have a veneer, we approach it with caution,” Hoppe says. “If you flood it, you’ll soften up the glue, and it will blister. We’d rather do four times with a sponge or a stain pad than two times painting it on.”

All bleaches will raise the grain slightly, so sand lightly with 220-grit before the next finishing step.

Wood conditioner ensures an even color
Whether you bleached the wood or not, if you apply stain to raw wood, the more porous parts will absorb more stain and show up as dark blotches on the surface. Wood conditioner, sometimes called stain controller, is a sealant that fills the pores uniformly so that the stain is absorbed evenly.

Minwax, Valspar, and Old Masters, among other companies, market sealants that are specifically formulated for use as wood conditioners. Some are meant to be used with oil-based stain and others with water-based stain, so make sure you get the right kind. Some painters prefer to use a light or diluted coat of another sealant, such as shellac. Bob Hoppe doesn’t often use wood conditioner, except on pine and maple, two woods that tend to absorb oil-based stain unevenly. “In oil-based stain, the [particles] are smaller, and they dive into the wood pores and make it blotchy,” he explains. Hoppe, who teaches classes at Faux Masters using Faux Effects products, gives these woods a coat of Faux Effects FX Thinner to close the pores evenly. Then he makes his own stain out of FX thinner and aniline faux colors. “I can make it so it is not super concentrated and it will stain nice and even. It doesn’t let me stain it very dark, but often people don’t want that.” Whatever conditioner you use, it shouldn’t require sanding before the stain is applied.

Try making some sample boards to get a feel for what bleaches and wood conditioners will do. Although these products add another application step to a job, they also provide the control and uniformity that separate professional painters’ work from do-it-yourself projects.