Wet sandpaper provides the smoothest finish of all sandpaper products. A mainstay of auto-body shops, it's also used for wood finishing when only the glassiest finish will do.
Wet or Dry
Sandpaper categorized as wet can also be used dry. Water or a water-detergent mixture reduces scratches by lubricating the surface. Water washes away loose abrasive grit, and in the process, prevents sandpaper from loading up with gunk and becoming ineffective.
Part of a Process
The use of wet sandpaper is part of a process in which sanding is done between each coat of polyurethane, varnish, lacquer or other top coat, with a progressively finer grit to remove surface imperfections.
Starting From Scratch
Step 1: Apply The Top Coat
Apply a finish of your choice to wood. High-gloss products sand to a brighter, glassier finish than semi-gloss or satin. Allow the product to dry according to label directions, or overnight.
Step 2: Mix With Soap
Pour about a 1/2-inch of water into a small tray. Add two drops of liquid dish soap and stir lightly.
Step 3: Sand with 500-Grit
Attach a strip of 500-grit wet sandpaper to a hand-sanding block. Hard rubber sanding blocks work best. Dip the block into the soap and water solution. Sand the wood lightly with a circular motion. Continue dipping the block into the water to keep the surface of the wood wet.
Don't tip the sanding block, or sand around corners or edges. The edge of the block may sand through the finish.
Step 4: Dry and Examine
Periodically wipe the surface of the wood dry to inspect it. When the surface has a uniform, consistently dull appearance, wipe it off and allow it to dry.
Step 5: Second Coat of Finish
Apply a second coat of your chosen finish, and allow it to dry overnight, then sand and wipe it again. Apply a third coat of finish and allow it to dry for at least 48 hours. It's essential that it's dry.
Step 6: Sand with Lighter Grits
Attach 1000-grit sandpaper to the sanding block. Repeat sanding as in Steps 3 and 4. When the surface is consistently dull, attach 1500-grit and repeat sanding and dipping. Finish by wet sanding it with 2000-grit sandpaper. Buff it dry with a soft cloth.
Don't spare the sandpaper. If it gets gunky or smooth it won't sand. Change it as often as needed.
Step 7: Polish if Desired
Polish it to a bright sheen with woodworkers paste wax or an automotive wax if desired.
Although wet sanding cuts down on air-borne particles, it's advisable to wear eye and breathing protection when working with wet sandpaper.