3 Ways to Patch a Scratch
Begin your repair by assessing whether only the film layer is damaged, or both the film and stain, exposing the wood. To test, wipe the damaged area with mineral spirits, as shown above, or just a dab of spit. Then choose a repair based on the following:
- No change in color. Good news, the film finish wasn't penetrated down to the wood fibers. Go to Fix #1.
- The color changes to match the undamaged area. More good news. Scratches penetrated the film finish, but the wood underneath either wasn't stained or no wood fibers broke. Go to Fix #2.
- The damaged area turns darker than the surrounding finish. This deep scratch broke wood fibers. Go to Fix #3 after reading the rest of this section.
Before starting the second or third fix, determine which type of film finish was used. Perhaps you recall this for projects you built. If not, check whether it's a lacquer finish by dabbing a hidden spot with lacquer thinner. If the finish softens, it's lacquer. If denatured alcohol softens the finish, it's shellac. If there's no change and the piece is fairly new, you likely have a water-based or polyurethane finish.
If you don't know the stain, apply comparable colors to scraps of the same wood species until they match. Before starting all repairs, liberally apply mineral spirits with clean cloths to remove any built-up wax or spray polish.
Fix #1: Paste wax for scuffs and shallow scratches
Cover up minor marring or scratches on a film finish using paste wax tinted about the same color as your project. (See Sources.) For a light scuff, use a soft cloth to apply the wax. For deeper scuffing, gently apply the wax with 0000 steel wool, as shown below. Allow the wax to harden, and buff it with a soft cloth to even sheen. If this produces a sheen that's different from the surrounding area (see "What is sheen?" on the last page), wax the entire surface with a soft cloth.
This method has one drawback: It doesn't repair the damaged area so much as cover it up. Should you later decide to repair the surface by dabbing on finish as in Fix #2 or applying another coat of finish, you'll first need to wipe away all traces of the wax with generous amounts of mineral spirits and soft, clean cloths.
Fix #2: Fill in a film finish
Some film-finish dings are too deep for paste wax to cover, but they still don't break the wood's surface, as shown below. Using a fine-tip applicator (see Sources), dab a small amount of matching finish only on the damaged area, as shown below. Lacquer and shellac patch easily with this method because the freshly applied finish partially dissolves and bonds with the topcoat. Continue dabbing on layers of finish until the patched area becomes level with the surrounding finish.
Use a similar method to touch up dinged polyurethane and water-based finishes, which don't redissolve earlier coats and level themselves. Dab on additional finish and allow it to dry. If there's still a slight depression after the finish dries, gently wipe the patch with 0000 steel wool and apply a second coat. If the patch stands proud of the surface, lightly sand it flush with 400- and 600-grit abrasives. Then restore the sheen of the patched area to that of the surrounding surface by sanding with progressively higher grits and, if necessary, rubbing compounds. A coat of paste wax also can help blend the patch with the rest of the surface.
Fix #3: Rebuild the finish from bare wood
If the mineral spirits wipe test turned the scratch into a dark streak, the wood fibers have been severed and the severed ends are soaking up the mineral spirits. Deep damage requires extensive repairs.
If there's only one scratch and fibers don't protrude from the surface, first seal the damaged area by dabbing on a 50-50 mix of film finish and the appropriate solvent. Then restore color to the scratch by dabbing on the original or a matching stain using a fine-tip applicator until you match the color. Allow the stain to dry thoroughly; then seal it by dabbing on topcoat as in Fix #2.
For multiple moderate scratches, as shown below, consider sanding the damage down to bare wood using 120-grit abrasive. Sanding with a finer grit may produce a lighter surface when restained. Avoid sanding too much over the damaged area and creating a visible depression in the wood. For extensive damage, sand the entire damaged surface to bare wood and refinish it to match.
For smaller repairs, though, begin restoring the color by wiping the bare wood with stain. Carefully wipe the stain to the edge of the sanded area. Avoid staining the feathered edge where the film finish meets bare wood, or you'll leave a darkened halo around the patch.
If the stain wipes on too light and the pores are not being filled to match the surrounding wood, scrape a small amount of pigment from the bottom of the stain can. Pigment colors may vary from the dye in the stain (dye color doesn't settle as pigment particles do), so add pigment carefully to a cloth moistened with stain. Then wipe this mixture over the previously stained area to darken it.
Using a back-and-forth motion, add and then partially wipe off enough coats of stain that the color—while still moist—matches the undamaged surface. If you apply too much stain, wipe it off immediately with mineral spirits and allow the surface to dry. Build color gradually rather than deposit too much at one time.Allow the stain to dry completely before spraying or brushing on a topcoat to blend the sheen of the patch with the surrounding surface, as shown in photo beow. If necessary, recoat the entire surface for an even sheen.
What is Sheen?
Sheen refers to how much light reflects off a surface. To hide your repairs, you'll need to match the sheen of patched areas to the surrounding finish as carefully as you match stain color to the rest of the surface.
A glossy finish, like the one right, bounces more light back to your eyes than a flat finish, which disperses the light. You can control sheen by choosing a flat, satin, semigloss, or gloss finish, each containing different amounts of flatting agent.
That's not the only method, though. You also adjust surface sheen by how smoothly you rub out a film finish with abrasives, and that's what complicates repairs. During the repair, if you rub the damaged area with sandpaper or steel wool and alter the surface sheen, that calls as much attention to itself as an off-color patch.
Avoid inconsistent sheen by using the same abrasive on the patched area as you used to finish the surface when the project was built. Paste wax can offset minor sheen differences, but extensive repairs may require refinishing the entire surface around the damaged area.
Tinted wax: Briwax in nine shades, Woodcraft, 800-225-1153 or woodcraft.com. Fine-tip applicators: Microbrushes ranging from superfine to small brush sizes, Lee Valley Tools, 800-871-8158 or leevalley.com.