AW Extra 1/10/13 - Repairing Finishes

Revive a dull finish

All finishes dull as they age, but you can usually bring back their shine. The easiest way is to apply paste wax. If the dulling has progressed too far, however, you must rub the finish with fine abrasives or apply another coat or two of finish.

To rub a finish, choose an abrasive that produces the sheen you want. You can use a powder, such as rottenstone or pumice, steel wool or a commercial rubbing compound. Rottenstone produces a glossy finish; pumice and #0000 steel wool produce a satin finish. Use mineral oil or mineral spirits as a lubricant with rottenstone, pumice or steel wool. Commercial rubbing compounds don’t require an additional lubricant.

If you must recoat the finish, be sure the surface is clean. Wash it with mineral spirits to remove grease and wax. Wash it with soap and water to remove sticky dirt. Then apply the finish you originally used, or apply oil, shellac, water-based finish, or any type of varnish, including polyurethane. Lacquer is risky to apply because lacquer thinner may cause the old finish to blister.

Remove felt-tip pen marks

Felt-tip pen ink almost always dissolves in alcohol, acetone or lacquer thinner. Any of these solvents can be used to remove marks on a wood finish, but because acetone and lacquer thinner damage most finishes, it’s best to use denatured alcohol. Shellac is the only finish this solvent will damage.

To remove an ink mark, simply dampen a cloth with denatured alcohol and wipe it lightly over the colored area. To reduce any chance of damage, avoid making the finish wet with alcohol. A light wipe or two should remove all of the ink.

Rub out white marks

White marks may be caused by water or heat. Water-created marks are easier to repair because the damage usually doesn’t go very deep.  

Water marks are usually caused by sweaty glasses. They’re almost always confined to the finish’s surface, so they’re easy to remove by rubbing with an abrasive. If the surface is glossy, try rottenstone and mineral oil on a cloth, or toothpaste on your finger. If these abrasives don’t cut fast enough, use #0000 steel wool to cut through the damage quickly, then restore the finish’s gloss by rubbing with rottenstone and mineral oil. If the surface is satin or flat, abrade with  #0000 steel wool and mineral oil. If you can’t get the sheen of the damaged area to match the rest of the surface, rub the entire surface with the same abrasive.

White marks caused by heat damage go deeper into the finish than those created by water. They’re more difficult, and sometimes impossible, to remove by abrasion. You may have to strip and refinish.

Remove crayon and candle wax

Wax dissolves in mineral spirits, naphtha and turpentine—none of which damage a finish when used sparingly, so they’re the best solvents for removing crayon marks. Mineral spirits is less expensive and more widely available than naphtha or turpentine. To remove crayon wax, simply dampen a cloth with mineral spirits and wipe it over the surface.

Candle drips are usually too thick for a solvent to be effective. It’s much faster to freeze or scrape off most of the wax and then clean up any remainder with solvent. To freeze wax, hold an ice cube on it for a short time, then pop off the wax with your fingernail. To scrape wax, use a credit card or any hard-edged utensil or tool, but be careful to avoid cutting into the finish.

You can also use a blow dryer or heat gun to soften wax. Be very careful with a heat gun because it can blister the finish. Clean up any remaining wax residue with one of the solvents.

Match colors on glass

Replacing missing color usually involves color matching, which most people find difficult. To make it easier, do the color matching on a small piece of glass or rigid, clear plastic placed on a part of the surface you’re matching. Use an artist’s brush to mix several colors until the blend matches the color underneath the glass or plastic. Brush the colorant onto the damage and protect it by applying a finish.

For the colorant, you can use concentrated oil, acrylic, universal or Japan colors, available from woodworking suppliers and paint and hobby stores. Or you can blend ready-made stains. 

Touch up a scuffed edge

Sharp edges are easily scraped. A scrape may not damage the wood, but it often removes the wood’s stained color, leaving a light area that stands out like a sore thumb. To repair the damage, simply drag an appropriately colored felt-tip marker over the damage. If the marker is pointed, use its side. This fix also works well with new finishes if you’ve accidentally sanded through a stained edge.

Felt-tip markers in various wood tones are available from most woodworking suppliers and home centers (see Source, below). “Magic” markers rarely match wood tones so they are seldom a good choice.

After the marker repair is thoroughly dry, apply some finish to protect the color from being rubbed off. Wiping varnish is easy to apply and won’t smear the color. You can make your own by thinning any regular or polyurethane varnish with mineral spirits. Mix equal parts of varnish and thinner. Dampen a cloth wrapped around your finger with this mixture and drag it along the repaired edge.

Remove dirty discoloration

Discoloration around drawer and cabinet-door pulls, or on chair arms and backs, may simply be dirt that’s easy to wash off with soap and water. On the other hand, it may be dirt mixed with deteriorated finish. In that case, the finish may have to be removed and replaced. 

The first thing to do is to wash the dirty area with a mild soap and warm water. Ordinary liquid dishwashing soaps are best. If this doesn’t remove the discoloration, the finish is probably deteriorated. Many finishes break down under extended contact with acidic body oils. In addition to being discolored, the finish may be soft enough to scrape away with your fingernail.

Sometimes you can remove the top layers of a deteriorated finish using fine sandpaper or steel wool, but if the finish has deteriorated to the wood, you usually have to strip and refinish the entire surface.

Remove crazing and light scratches

Film finishes craze with age. That is, they develop a tight pattern of cracks similar to what you’d see on an old oil painting. 

If the cracks are shallow, and don’t penetrate through a layer of color, they may be sanded out. Light scratches can be removed in the same way.

Choose a sandpaper grit coarse enough to efficiently cut through the damage but not so coarse that you create large scratches or risk sanding through to the wood. The best choices are usually 320- or 400-grit stearated sandpaper (3M Tri-M-ite or Norton 3X), or 600- or 1000-grit wet/dry (black) sandpaper. Use stearated sandpaper dry and wet/dry sandpaper with a lubricant of mineral oil or mineral spirits. Dry sanding lets you see your progress better so you are less likely to sand through.

Begin by sanding a small part of the surface to test that you’re using the correct grit. Then sand the entire surface. Back the sandpaper with a flat block only if the surface is flat, or you may sand through high spots. When you have removed the crazing or scratches, rub out the finish or apply new finish.

Remove stickers and tape

Stickers and tape may not neatly peel off if they’ve been stuck to a finish for a long time. Here are several methods for removing them.If a sticker is made from paper, wet it for a few minutes and try rubbing it off with your finger. If this doesn’t work, or if you’re dealing with tape, try heating with a blow drier or heat gun to soften the adhesive. (Be very careful with a heat gun because it can blister the finish.)

Once the bulk of the sticker or tape is gone, remove the remaining adhesive with naphtha, toluene or xylene. (Don’t use acetone or lacquer thinner; they may damage the finish.) Products designed to remove latex paint spatter, such as Oops! and Goof Off, may also work. None of these solvents will damage any finish except a water-based one, but try them out on a hidden area first. If the sticker or tape is very stubborn, try working one of these solvents under it. If these methods don’t work, you’ll have to sand or scrape off the sticker or tape and repair the finish.

Repair color damage

There are at least four methods of repairing color damage in finished wood. The first step is to determine which method works best. To do this, apply a liquid to the damage and see what happens. 

The best liquid to use is mineral spirits. It won’t damage any finish, and it penetrates any wax that might be on the surface to give a more accurate diagnosis. Liquid from your mouth also works well, so I call this the “spit test.” When you dab any of these liquids, one of four things will happen:

1) The color comes back. That’s great, because the solution is merely to apply some finish.

2) The color only partially comes back. You’ll have to stain before putting on more finish.

3) The color doesn’t change. Stain won’t work. You’ll have to “paint” in the color with a colored marker or artist’s brush before applying finish.

4) The color gets too dark. The best fix is to apply clear paste wax, or seal the damage with a fast-drying finish such as shellac, then coat with the finish of your choice. 

Fill gouges with epoxy

The easiest method of filling dents and gouges is using an epoxy stick. Sticks are available in a variety of colors from most woodworking suppliers and home centers (see Source, below). Here’s how to do it.

First, level the surface. That is, remove all roughness at the top edge of the gouge. Then cut enough material from the epoxy stick to do the job. You can blend different colors to match your wood. Knead the epoxy until it’s a uniform color.

Press the epoxy into the gouge leaving a slight rise above the wood’s surface. Dampen the epoxy with water, then remove the excess by scraping the filled area with a credit card or plastic putty knife. You can also level the epoxy by sanding after it hardens, backing your sandpaper with a small flat block. Sanding usually damages the finish around the fill, though.  

Sources

(Note: Product availability and costs are subject to change since original publication date.)

This story originally appeared in American Woodworker May 2007, issue #128.

May 2007, issue #128

Purchase this back issue.