I wouldn't use a PC for Wetsanding anything, but there are Air Powered DA sanders made for the purpose.
I always advise folks before they take up this task to understand the objective when wetsanding as it's quite easy to "cut" through to the under lying substrate which will require the re-application of the material that was being sanded (in the case of Clear Coat that would be a PITA).
That objective is to just make the material (in your case Primer) smooth.
You'll need a bucket of water (with a couple of drops of Dish Soap added for lube, just a smidgen your not washing anything with it).
Primer is sanded wet with P600 Grit Wet/dry Sandpaper so you'll need some of that in addition to something to wrap the paper around. I use either a
3M Wetordry Rubber Squeegee or a
Motor Guard Memory Block MB-1. Others just use a flat piece of wood that is of sufficient length.
Having a water source like a garden hose around helps to wash down the surface between attempts so your flushing the "sludge" away as you work.
Let the paper soak in the water/soap mix over night or at least several hours prior to use to soften it up. As usual make sure the surface is clean so you don't get something caught in between the paper and the surface causing scratches.
Now that you've got everything set up it's time to go to it. Wet down the panel and wrap the sandpaper around the squeegee or block taking care you don't leave any hard edges exposed. Now just start sanding. Work sections at a time.
The key here is to remember your "wet" sanding so the paper and the surface needs to stay, well, wet. So keep dipping the paper back into the bucket of water and make sure your rinsing away the sludge buildup. You don't have to un-wrap it each time.
At first you'll feel the paper "grabbing" into the surface. This is the friction between the uneven material on the surface and the sandpaper. As you continue the resistance will lessen. Check your progress often. This is where having a squeegee comes in handy cause you can just use it to clear the water and sludge off the surface.
The Primer should have a smooth feel to it and no texture. It will actually begin to develop a shine or gloss. That means your done. Once the entire panel is finished, wash it down the way you would normally using a PH Balanced Car soap (don't use anything like the "wash and wax" type stuff is it could leave contaminates that will interfere with the painting process.
Remember when wetsanding Primer you only want to remove the texture and that's it. People can and have sanded too much and went right through the Primer or Clear Coat. Which as I mentioned earlier means you'll have to clean everything up get it dry and re-apply more material to the area where the "cut through" is.
HTH
Greg
