Power your way to a polished finish

Some woodworkers brush on a few coats of varnish and wonder why their finish doesn't look gallery-smooth. Truth is, a silky film finish starts where the label directions stop. After the final coat cures, a savvy finisher traditionally digs out his pumice or rottenstone (powdered abrasives) and lubricant, and hand-rubs the finish to an even sheen without dust nibs, runs, or a "plastic" look. If that process seems time-consuming and messy, you can see why most guys rub out only horizontal surfaces, such as a tabletop, where light best reflects off the finish.

For a faster, cleaner method, try the techniques used by auto-body experts. Instead of oils, powders, and handheld rubbing blocks, they use premixed automotive polishing compound and a foam buffing pad on a dedicated polisher. You can achieve similar results using your random-orbit sander.

You can rub out nearly any film finish, including polyurethane, lacquer, and shellac. With the latter two, each topcoat bonds with the one beneath it to form one single layer. With poly, though, you'll want to apply a full-strength final coat to avoid cutting through to the layer below.

Although a rubbed finish solves some problems, it highlights others if you shortchange the surface preparations. For example, a porous wood, such as red oak, looks pockmarked because the pores don't fill with finish. To prevent that, always seal porous woods with a coat of the finish you'll use for your topcoat. Then fill the pores with a commercial compound such as Behlen's Por-O-Pac. (See Sources, below) Follow that with three coats of film finish as close to full strength as you can apply.

Brush on each coat as evenly as possible close to the edges to avoid sanding or rubbing through the finish there. However, avoid applying extra-heavy coats. Yes, thick coats protect against sand-through, but they also drip and sag more than moderate coats. And a heavy finish takes longer to cure.

Rubbing only works on a fully cured film finish. On anything less, you'll only smear the finish instead of polishing it. To tell when a finish has cured, sniff it. If you smell solvents, it needs more curing time.

Your random-orbit sander handles occasional jobs rubbing out a finish, but you'll speed the process even more using a dedicated electric polisher. A polisher for rubbing out furniture finishes should have a variable-speed control for slow-speed work that won't overheat your finish. Attach yellow buffing pads to the rubber backer using the center washer nut, or replace the original pad with a hook-and-loop aftermarket pad.

Begin sanding the finish with 220- or 320-grit stearated sandpaper to remove dust nibs, brush strokes, and runs or dips, top photo, below. If you use a random-orbit sander with 220- and 320-grit discs, watch for build-up on the abrasive, middle photo below. This can form lumps, called "corns," that mar the finish instead of smoothing it. Stop immediately and clean the disc if you see loops in the surface dust, bottom photo below.

After you reach the 400- through 1,000-grit abrasives, switch to hand-sanding with wet/dry sandpaper lubricated with mineral oil. Sand with the grain, and clean the surface using mineral spirits and a soft, clean cloth after each grit.

Note: As you gain finish-sanding skill using mineral-oil lubricant, save time and mess by switching to a lubricant that lets abrasives cut faster. Make your own from 1 tablespoon of dish-washing liquid in 1 quart of water. Be careful: Fast-cutting lubricants increase the risk of sanding through the finish. When you have an even sheen, you're ready to polish.

Place your sanded and cleaned workpiece on a non-skid mat to keep it from shifting as you polish. Then center and attach a yellow buffing pad (Sources) to the hook-and-loop pad of your random-orbit sander.

After shaking the container of polishing compound, squirt a moderate amount directly on the workpiece in an area the size of your polishing pad, photo below Place the foam pad on the compound and start your sander at its highest speed.

Press lightly and polish a workpiece section of about 3 square feet in overlapping circles, photo below. Go easy at edges and corners. Polish these areas just enough to reach the desired sheen, then stop before you polish through the finish.

Note: With polyurethane, sanding or polishing too long in one area can cut through the outer topcoat to the layer below and create a ring. If that happens, clean the workpiece thoroughly with mineral spirits, scuff sand it with 320-grit abrasive, and apply a full-strength topcoat. After it cures, sand as before and resume polishing.

The polish forms a powder as you work and the polishing pad will gradually leave a clear, smooth surface, photo below. In the reflection of an angled light, check for an even sheen and repeat for any missed spots.

After wiping the surface with a clean, soft cloth, add shine and remove the polishing compound residue by wiping on an automotive cleaner and polish. (See Sources.)

Sources
Pore filler. Behlen Pore-O-Pac Grain Filler in mahogany no. B744-1256 (other colors available), $19.95 per quart, Tools for Working Wood, 800-426-4613 or toolsforworkingwood.com.
Polishing compound. Wizards Turbo Cut no. 11044, Wizmar International, 800-356-7223 or wizardsproducts.com ($21 for 32 oz from Above All Wholesalers, 631-471-0318 or aawsales.com).

Cleaner and polish. Wizards Mist-N-Shine no. 1214, Wizmar Intl. ($14.25 for 22 oz from Above All Wholesalers.)
Buffing pad. 9" yellow buffing pad no. 91235-0VGA, $7, Harbor Freight, 805-388-3000 or harborfreight.com.
Electric polisher. DeWalt variable-speed polisher no. DW847 with a 7" backing pad, ($170 from Amazon.com), 800-433-9258 or dewalt.com.

FREE VIDEOS

• "Filled-Pore finish" woodmagazine.com/filledporevidt
• "Fix Flaws in Film Finishes" woodmagazine.com/finishfix

RELATED ARTICLES

• "Fill-Pores for an Even Sheen" Issue 181 (December 2007) or at woodmagazine.com/filledpore.

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