Sanding tips
Wet sanding is normally done by hand. Never use an electric powered sander when wet sanding or you could get electrocuted. We have used air-powered dual action (DA) machines for wet sanding (which is messy), but we usually sand by hand.

I use a hard rubber sanding block like the one in the photo to hold the paper when smoothing and abrading most surfaces. A curved or soft pad may be necessary on curved surfaces, but you can wet sand without a block or pad by simply folding the cloth to fit your hand and dipping the paper in water. On heavily irregular or textured surfaces such as a sculpture, the waterproof paper won't contour enough, so use an abrasive pad like 3M Scotch Brite™ with water.

I usually put water in a bucket. If the shop is cool, I'll put hot water in a cooler (it holds heat as well as cold) to help keep it warm. I dip the rubber sanding block with sandpaper attached into the water when more water is needed. Another approach is to fill a squirt bottle and spray the substrate as you're sanding.

Use a rubber-bladed window washer squeegee to scrape excess water and cut material from the substrate so you can visually inspect the surface better. When wet, the surface is shiny, but when squeegeed, it appears dull and highlights surface texture. When wet sanding, especially with aggressive grits, you have to keep an eye on your progress. Rinse and squeegee away water between changes in grit to avoid contaminating the finer grit with the previous coarser grit. Be sure to remove any remaining debris right after wet sanding because it's hard to remove after it dries. Rinse water should sheet evenly, without beading or fisheyeing. If rinse water beads up, wet sand again until the beading is eliminated.

To prepare the surface for subsequent epoxy coats or painting, wipe the dry surface with a paper towel to loosen any remaining debris and then sweep it with a bench brush. Don't use rags-they may contaminate the surface. Follow with an electrostatic dust cloth, such as a Pledge Grab-it™. We use a tack cloth prior to painting, but not for subsequent epoxy coats because the tack cloth is resinous saturated cheesecloth which can contaminate the substrate and interfere with epoxy adhesion.

Constant immersion in water softens your skin and makes hands more susceptible to cuts and abrasions. Wet dry cycles can also result in chapped skin. Use a dry skin cream such as Pond's™ to combat this problem. If you wet sand with the paper in direct contact with your skin, it's possible to abrade your skin away. I've been without fingerprints for a few days as a result. The upshot is, your hands will be cleaner than they've been in years, possibly with fingers a safecracker would envy.

Wet sanding can make a mess. All the cut debris in solution with water ends up on the floor. This is difficult to sweep up when dry. But the advantage, as mentioned before, is that wet sanding produces no dust.

Much of the quality of a final finish is in surface preparation. Wet sanding has much to be said for easing the task without sacrificing quality.