The Complete Guide to Automotive Wet Sanding

Wet sanding is the process of physically sanding the surface of your paint to remove imperfections. Wet sanding is a normal procedure in body shops . After a car is painted (clear coated) there will be imperfections in the clear coat such as orange peel, fish eyes, divots, clear coat run down etc. Wet sanding is done to remove these imperfections and prepare the paint for compounding/polishing.

The actual process of wet sanding involves using some type of automotive wet/dry sandpaper using water as a lubricant for the sandpaper. Similar to sandpaper for wood, wet sandpaper (or sanding disks) are available in different grits. The coarser the grit the faster the defects are removed. The downside to using a coarser grit is that the sanding marks will be deep meaning it will take much longer to remove these marks with your polisher. It is quite common (depending on the severity of the damage) to sand several times starting with a coarse grit to remove the defects, then with a finer grit to remove the sanding marks from the coarser grit. The finer a grit you sand down to means less time you will spend removing sanding marks with your polisher. If you do choose to wet sand your vehicle we recommend sanding to a minimum of 2000 grit before bringing out the polisher.

Wet sanding can be done by hand or with a sander. Unless you are very experienced with wet sanding we do not recommend using a machine sander to wet sand. The sander/paper

combination is very aggressive and it won't take long to burn through your clear coat if you are not familiar with using a sander to wet sand.

Hand Sanding

Machine Sanding

Paint Appearance after Sanding

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When Should You Wet Sand?

We quite frequently have customers tell us they are going to wet sand their vehicle to remove scratches from the clearcoat. Under almost every scenario this is a bad idea, specially on factory clearcoats! Wet sanding is very aggressive and will probably remove way more clearcoat than you need to in order to get those scratches out! Anytime you are removing scratches you want to do so saving as much of the clearcoat as you can. Remember this... most new cars have what is called a basecoat/clearcoat paint job. In this case, it is the clear coat layer that you would be doing the wet sanding to. From the factory, the clear coat layer is around 2 mils thin. Take a sticky note and hold it between your thumb and index finger.  A sticky note measures around 2.5-3 mils thin. The factory paint on your car is 2 mils or thinner. That’s right — the factory paint on your car is thinner than a sticky note. As the following diagrams show, wet sanding to remove scratches is going to remove more of the clear layer than just removing the scratches by machine compounding/polishing...

As you can see from the above diagrams wet sanding will still require a compound stage to remove the sanding marks left by the sandpaper plus a final polish to refine the finish. Once all three steps are complete you have removed a lot of the clearcoat layer.

As shown below if you remove those scratches just with a compound and polish you will be removing less clearcoat overall!

Keep in mind too that if you are choosing to wet sand because the vehicle has deep scratches in the hopes of speeding up the scratch removal process it is really not going to. Yes, if you sand your vehicle down to 3000 or 5000 grit sanding marks they will be removed with 1 or 2 passes (polishing an area) with your polisher and compound whereas it may take 3 or 4 passes (more time involved) to get out deeper scratches with compounding alone. However, when you add up the time required to wet sand plus you will still need to compound out the sanding marks after wet sanding, it is actually still a lot quicker overall to just spend the extra time needed with a compound & polisher to get those scratches out.

In the detailing world wet sanding is most commonly used to remove orange peel from paint. This paint defect is called orange peel because it has the appearance of the peel of an orange.

Orange Peel

Contrary to scratch removal (where the polisher/compound solution is recommended) trying to remove orange peel with just your polisher and a compound is very time consuming and is not recommended (there is a method of removing orange peel with a polisher that will be explained below). With orange peel you are trying to shave off those bumps to level & smoothen the paint. Standard cutting compounds and pads are designed to remove larger areas of paint at one time so are not very effective at shaving off that excess paint causing the orange peel. Wet sanding is the preferred option for quickly shaving off the orange peel and levelling the paint.

If you do want to remove orange peel with just your polisher CarPro does make a special pad designed for removal of orange peel with a polisher. Its the CarPro Denim Orange Peel Removal Pad. This is a very aggressive pad that when used with a cutting compound provides the equivalent aggressiveness of 2000 grit sand paper. These pads come in 5" & 3" sizes and will attach to any standard backing plate. Instructions on how to use this pad can be found below...

CarPro Denim Pad

CarPro Denim Pad

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How to Wet Sand

If you do decide to wet sand your paint we recommend hand sanding unless you are very experienced.

What You Need:

1. Sanding paper or disks (for heavy orange peel sand first with 1000 or 1500 grit then finish with 3000 or 5000 grit)

2. Sanding block (this can be anything from a flexible rubber pad to a foam block)

3. Bucket with water

4. Car wash soap

5. Access to a water hose

6. Microfiber towels

7. Automotive masking tape (to mask off trim etc. to prevent accidental damage)

Make sure you wash the vehicle first. The damage that you are trying to repair will dictate how much sanding will be required, and with what type of paper. Significant clear coat damage will require multiple steps, but light scuffing can be resolved in one stage.

• If the damage to the paint is heavy start with between 1000 & 1500 grit paper, then follow up with 3000 or 5000 grit paper to refine the paint before compounding

• If the damage appears to be light skip the 1000 or 1500 grit sandpaper and begin with 3000 grit paper instead.

Step 1 - Taping

If you are sanding just one panel of the car tape off that panel to prevent accidentally sanding areas that do not require it. If you will be sanding near trim tape off the trim to prevent damage.

Step 2 - Wet the Paper

Fill a bucket with water and add a small amount of automotive soap. The soap will help lubricate the sandpaper to prevent it from burning the paint when force is applied. Soak the paper for about 5 minutes.

Step 3 - Sanding

Wrap a sheet of paper around your block of choice. Do not sand with just your fingers alone. Backing pads should be used across larger flat surfaces to provide even pressure so you don’t create waves with your fingers.

Sand in a straight back-and-forth motion, applying light pressure as you go. As the sandpaper is moved over the paint surface, the highest points of the paint are removed, leveling the surface to make it flat. It can take time to determine how much pressure is required, so take your time with this step. Too much pressure can remove too much clearcoat!

Do not allow the sandpaper to become dry while wet sanding. Keep the area heavily saturated with soapy water throughout the process by dipping the sandpaper in the bucket often and even pouring some of the soapy water on the vehicle. If the paper gets too dry

it will produce heat which can burn the paint. Swap sheets of sandpaper out for new soaked ones as they sandpaper becomes worn out or too soggy to use.

Rinse the area frequently to remove the clear coat sediment that builds on the surface as you sand.

Be very cautious around edges. Try to avoid sanding any edges on panels. It is very easy to quickly burn through these areas.

Once the sanding marks left behind by wet sanding are polished out, the paint will exhibit a high level of shine with little to no texture visible.

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Remember: For scratch removal polishing is the preferred method. For orange peel removal wet sand. There you have it. The complete guide to wet sanding. See our other blog posts for more information on the compounding/polishing process. Happy Detailing!