How to Wet Sand Your Car's Primer or Paint

01
of 02
How It's Done

Sanding supplies
The only equipment you'll need is a spray bottle and sand paper. Photo by Matt Wright, 2013

Wet sanding is an amazing process that, when done properly, can result in a surface that's as smooth as glass. Whether you're talking about paint, primer, bare metal or anything in between, your car's body can be smoothed by wet sanding. Let's get down to the process of wet sanding, also known as color sanding when using this method to add shine to a finished paint job. First we'll talk about what you need to get the job done, then I'll tell you the finer points of the sanding process. Finally, we can get into the esoteric side of body finishing and sanding.

What You'll Need:

  1. A car or truck that needs some smoothin'
  2. Spray bottle filled with water
  3. Wet sandpaper in varying grits

 

Good spray bottles can be bought at just about any store you can think of. Home repair stores always have them, but other box stores and grocery stores usually have bottles in the cleaning section. Be sure to buy a bottle that has an actual spray pattern. In other words, you don't want a spray bottle that throws a thick splash of water, rather you need more of a misty sprayed pattern that can saturate your work surface while you use one hand for spraying and the other hand for sanding.

Choosing what grit sandpaper to use is important. If you start with a grit that is too coarse, you'll be creating more work for yourself and might be left with a thinner paint or primer coat than you wanted. Start with too fine a grit and you'll be sanding until your arm feels like it's going to fall off. A little experimentation will help. As a starting point, if you are sanding a coat of rough primer, you can start with a 400-grit sand paper to knock down all of those little bumps. After some time with the 400 grit, you can move to a 600-grit paper to give yourself a nice, smooth surface to work with when you are painting the car. If you are wet sanding a finished paint job, you definitely do not want to start with a 400 grit sand paper. Too harsh! You'll be ruining your paint finish just so you can do lots of work to restore it again. For a finished paint job that just needs a little more smoothness and shine, start with an 800, or even a 1000 grit sand paper.

Remember, when sanding anything, it's always important to take it slow. Let the sandpaper do the work, and don't apply too much hand pressure as this can cause grooves or uneven sanding. And we both know what that amounts to -- more work!

02
of 02
The Backs and Forths of Wet Sanding

Wet sanding auto paint
Wet sanding require water and a back and forth motion. Photo by Matt Wright, 2013

With your materials chosen and bought, you're now dedicated to the project. After all, you've now spent almost $10 on your wet sanding project, no turning back! Unless you have a very nice garage with a drain in the floor and nothing at all stored in it, you will probably want to conduct all of your wet sanding outside. The water that runs off as you sand the paint's finish will be full of tiny bits of paint that can stain the floor and be difficult to clean up once dry.

Before you begin it's always a good idea to wash your car to remove anything that you don't want to mix into the sand paper like wax, grit or other foreign matter. If you've been doing any body work there might be tape residue or other leftovers waiting to corrupt your efforts. With a clean car you're ready to dive into the process of wet sanding.

The simple fact about wet sanding is, well, it's sanding a car with water! The water acts as a lubricant and vehicle to remove the paint dust that would normally just clog up the sandpaper and get in the way. Start by liberally spraying an area a couple of square feet in size with your water-filled spray bottle. Choose your coarsest grit (600 if you are sanding primer or body work, 800-1000 if you are sanding a finished paint job). Spray the paper itself, then start gently sanding the body of the vehicle. Unlike other types of sanding, wet sanding movements should be back and forth, in a straight line, rather than in circular motions. Don't apply too much pressure to the sandpaper. Sand back and forth within the same area, adding more water often. It can never be too wet. After a few minutes, run your fingertips across the sanded area and be amazed at how smooth it's become. Repeat this over the whole car, then repeat the process with your next finest sand paper grit. When you're finished, rinse the entire car well to remove all of the sanding dust. Done!