Wet-Sanding
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Wood Magazine

Wet-Sanding

Seven steps to a heavenly finish.

Step 1

Step 1

For most of us, finishing means applying varnish, polyurethane, or paint with a brush. The dream of a glass-smooth tabletop is always spoiled by brush marks and bits of dust and other debris. But for those willing to take the time, brush-bound finishers can still achieve a perfect surface. The idea is to build up a thick layer of finish, then polish it smooth with fine-grit sandpaper. Here's how.


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1. Sand the surface to 320-grit. Thoroughly remove sanding dust from the pores of the wood using compressed air of a shop vacuum and tack cloth.


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Paste wood filler, top center, makes a smooth foundation for the finish. Wet-sand with a simple solution of liquid detergent and water, left, using a rubber sanding block, bottom center. Polish with an automotive wax, bottom right.


 

Step 2
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Step 2

2. When using open-grained woods, such as oak, ash, mahogany or walnut, fill the pores by applying a paste wood filler like J.E. Moser's Grain-Fil. See the Buying Guide at the end of the article. Use a plastic scraper, working across the grain, to pack the filler into the pores as shown in Photo A. Remove excess with a squeegee, once again working across the grain, as shown in Photo B, to avoid pulling the filler dry overnight, then sand lightly with 220-grit sandpaper. Apply a second coat of filler, removing the excess with the squeegee as before. When the filler is dry, sand again with 220-grit sandpaper.


 

Steps 3-7
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Steps 3-7

3. Apply a finish of your choice and let it dry overnight. We tested this technique on oil-based spar varnish, oil-based polyurethane, waterbased polyurethane, and oil-based enamel paint. Any sheen -- gloss, satin, or semigloss -- will work. You can bring gloss finishes to the brightest sheen. The flatting agents in satin and semigloss finishes prevent them from being worked to attain a high gloss.

Left to right: You can work enamel paint to a bright automotive-style finish. Shown on white ash veneer, water-based poly goes on perfectly clear; oil-based poly and spar varnish add progressively more amber cast to the wood grain.


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4. Now it's time to "knock down" brush marks, drips, or dust flecks in the finish. Put about 1/2" of water in a shallow plastic tray and add a couple of drops of liquid detergent. The detergent, by reducing the surface tension of the water, allows it to more effectively wet the sandpaper and the tabletop and be a better lubricant. Dip 500-grit wet/dry paper (see box on page 4 on wet-sanding) backed with a rubber sanding block (available at hardware stores and home centers) into the detergent solution and work the surface in a circular motion, as shown in Photo C. Be careful not to oversand the edges. Keep the sandpaper wet with clean detergent solution. Periodically wipe the surface dry to inspect it. When the surface has a uniform dull sheen, wipe it clean with a damp sponge and let it dry.

5. Apply a second coat of finish and let it dry overnight. Wet-sand again as in Step 4 and wipe dry. Now apply a third coat of finish, but this time, let it dry two days to make sure the entire film of finish is dry.

6. Just as in Step 4, wet-sand the surface, this time starting with 1000-grit wet/dry sandpaper, progressing to 1500-grit and finally 2000-grit. Buff with a clean, soft cloth.

7. Get out the car wax and apply and polish it, as shown in Photo D, according to the directions. (We used Turtle Wax, but any automotive cleaner/wax will do.)


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Why Sand Wet?

Why Sand Wet?

Borrowing from the bodyshop. Resin-impregnated sandpaper, in grits ranging from 320 to 2000, is available from auto-body paint and supply stores. The abrasive particles on these sandpapers are of a more uniform size than those of common woodworking sandpapers and are more securely bonded to the backing paper.

This wet/dry sandpaper can be used either dry, like common woodworking sandpaper, or wet, using a rubber sanding block and solution of liquid detergent and water. Wet-sanding lubricates the surface being abraded, reducing scratches. The water also carries away loose pieces of abrasive as well as finish particles and prevents the sandpaper from loading up.


 

Buying Guide

Buying Guide

J.E. Moser's Grain-Fil, available in quarts from

Woodworker's Supply 1108 North Glenn Road Casper, Wyoming 82601-1698 Phone: 800/645-9292

Item no. 922-828, $17.95 plus $6.50 shipping. Residents of WY, NM, NC please add sales tax.


 

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