Wet sanding is a sanding process that uses water or another liquid as lubrication to wash away grit particles. Without the liquid, the sandpaper can build up with material, causing scratches that ruin the finish.

In general, the best liquid to use for most materials is water with a little bit of detergent in it. By lowering the surface tension of the water, the detergent reduces scuffing and helps wet paper and material more completely. WD-40 can be used as a lubricant instead of water if you're sanding bare metal. 

At Red Label Abrasives, we get a lot of questions about the process, namely, “What is wet sanding and why do it?” This blog explains the purpose of wet sanding, how you do it, and how the process differs from one material to another.

Why Wet Sand?

The purpose of wet sanding is to get an even surface finish after dry sanding. Dry sanding shapes the surface, while wet sanding removes the large scratches left by dry sanding. If done correctly, the surface will gradually level out, and the scratches will become smaller and smaller until they are no longer visible when the light reflects off of them.

It is important to use sandpaper that is specifically rated for wet sanding. The sandpaper can be folded over on itself to make a thicker piece, but it is even more effective if wrapped around a backing pad. Another option is to use sanding sponges with the abrasive already attached. By doing so, the sanding surface is able to conform to the shape of the material more easily.

To thoroughly wet sandpaper, many people suggest soaking it overnight in liquid. By doing so, the paper will not absorb any more moisture during the sanding procedure. If you can't soak the paper overnight, aim for at least 15 minutes of immersion before sanding.

It should also be noted that the physical process of wet sanding is different from dry sanding. For an even finish, dry sanding uses small circles, while wet sanding uses linear movements and alternate directions between passes. This is done to remove scratches from previous passes. Wet sanding only removes surface scratches and not much material, so use a light touch.

Benefits of Wet Sanding

Smoothing clear wood finishes with wet sanding results in finer quality. A wet sander can be used after sealant, varnish, or polyurethane has been applied to smooth out bumps, scratches, or imperfections on the surface. In addition to making scratches less visible, the water gives better control over the thickness of the finish. If you’re looking for a more satiny finish, you can opt for oil instead of water.

Other benefits of wet sanding are highlighted below.

Better Dust Reduction with Wood

When used in home interior jobs, wet sanding reduces a lot of dust compared to dry sanding. In high-end interior painting, wet sanding is used before painting as well as between coats. After the sanding dust gets wet, it doesn't ruin the paint.

Supports Paint Correction for Automotive

Automobile surfaces are extremely fine and can scratch easily, so they need to be sanded with care. When restoring a car's finish, wet sanding is the best approach, provided that care is exercised during application. You can use it to remove paint defects and even out new paint jobs.

What are the Best Abrasives for Wet Sanding?

Not all abrasives are suitable for wet sanding. These applications require both a grit and a backing that’s suitable for wet environments. For example:

• Many of our orange hook and loop sanding discs are made with a premium waterproof polyester film and aluminum oxide abrasive grains. Their versatility makes them ideal for wet and dry sanding, and they're commonly used for auto body work.
• Our pressure sensitive adhesive (PSA) discs feature special waterproof polyester film aluminum oxide, closed coat silicon carbide, and closed coat zirconia abrasives. All are designed for excellent results in wet applications. 

Our Wet Sanding Discs

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5 Inch Adhesive Back (PSA) Blue Wet / Dry Sharpening Film Sanding Discs, 10 Pack

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6 Inch Adhesive Back (PSA) Blue Wet / Dry Sharpening Film Sanding Discs, 10 Pack

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6 Inch Hook and Loop Orange Wet / Dry Auto Body Film Sanding Discs, 10 Pack

from $12.59

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5 Inch Hook and Loop Blue Wet / Dry Sharpening Film Sanding Discs, 10 Pack

from $11.29

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5 Inch Hook and Loop Orange Wet / Dry Auto Body Film Sanding Discs, 10 Pack

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How to Wet Sand Metal Surfaces

Sanding metal wet is often the best way to remove minor scratches and refinish dull surfaces to a high sheen. Below is an overview of the basic steps involved, along with the supplies you’ll need.

Supplies

• Supply of clean cloths / rags
• Metal degreaser
• Orbital sander
• 180-grit sandpaper
• 320-grit sandpaper
• 460-grit sandpaper
• 600-grit sandpaper

Steps

1. To prepare the surface for sanding, wipe it down. Spray water on the surface and wipe it again. Apply metal degreaser and wipe with a clean cloth. Once again, spray the surface with water and wipe it with a clean rag.
2. Use an orbital sander with 180-grit sandpaper designed specifically for wet sanding. The attached sandpaper should be dipped into a small bucket of water--do not submerge the sander in water, as electrical shock may result. 
3. Spray water thoroughly onto the area to be sanded and stop as needed to add more. Using a slow, steady motion, sand the surface.
4. Wipe the surface with a rag after spraying it with water. Apply metal degreaser and a clean rag to the surface again.
5. Swap 180-grit sandpaper for 320-grit sandpaper. Dip the paper into the bucket of water. Sand the area again after spraying it with water. Keep your pace slow and steady and keep the surface wet--don't let it dry out.
6. Spray the surface with water and wipe it again with a rag. Apply metal degreaser to the surface and wipe with a clean rag.
7. Swap the 320 grit sandpaper for the 460 grit sandpaper. Dip it into the water bucket. Before sanding, spray the surface with water until it is completely covered.
8. Spray the surface with water and wipe it again with a rag. Apply metal degreaser to the surface and wipe with a clean rag.
9. Use 600-grit sandpaper instead of 460-grit. Dip it into the bucket and spray the surface with more water. This grit paper is best used to remove sanding marks and achieve a high sheen on the surface. After cleaning with water, use metal degreaser to finish.

How to Wet Sand Wood

Wood finishing typically involves applying varnish, polyurethane, or paint with a brush. Wet sanding can add an extra level of brilliance to wood surfaces. A thick layer of finish is applied, then polished smooth with fine-grit sandpaper. Here's how you do it.

Supplies

• Tack cloth
• Shop vacuum
• Belt sander
• 320-grit sandpaper
• 220-grit sandpaper
• 500-grit sandpaper
• 1000-grit sandpaper
• 1500-grit sandpaper
• 2000-grit sandpaper
• Wood filler
• Plastic scraper
• Plastic tray
• Squeegee
• Finish of your choice
• Car wax

Steps

1. Sand the surface with 320-grit abrasive. Using a shop vacuum and tack cloth, thoroughly remove sanding dust from the pores of the wood.
2. Fill the pores of open-grained woods, such as oak, ash, mahogany or walnut, with paste wood filler. Pack the filler into the pores using a plastic scraper, working across the grain. Remove excess with a squeegee and let dry overnight.
3. Use 220-grit sandpaper to lightly sand the surface. Apply a second coat of filler and remove excess with the squeegee. After the filler has dried, sand it again with 220-grit sandpaper.
4. Apply any finish you like and let it dry overnight. You can use any sheen, whether it is satin, glossy, or semi-gloss. 
5. Pour about 1 1/2 inch of water into a shallow plastic tray and add a little liquid detergent. Dip 500-grit paper on a sanding block into the solution and sand the surface in a circular motion.
6. Wipe the surface dry periodically to inspect it. If the surface has a uniform dull sheen, wipe it clean with a damp sponge and let it dry.
7. Make a second coat of finish and let it dry overnight. Again, wet-sand and let dry. After the third coat of finish is applied, let it dry for two days to ensure that the entire film is dry.
8. Once again, wet-sand the surface, starting with 1000-grit wet/dry sandpaper, proceeding to 1500-grit and then 2000-grit. Use a soft, clean cloth to buff.
9. Using car wax, apply and polish the surface as directed.

Get the Best Wet Sanding Results with Red Label Abrasives