Wet sanding primer

Since I finally got the engine going, I switched gears back to Summer Mode, which means countless hours of body work, sanding, and spraying.  This is the final summer for it however.

I am getting my panels ready for the sealer (reduced epoxy) before base coat and clear coat go on.  The hang up for me however--I only have two panels that are actually in 2k primer.  All the rest have Slick Sand--the poly primer--and I don't dare wet sand that.  I first attempted dry sanding these with 400 and literally spent HOURS sanding my hood.  What I've decided I'll do in this case is spray two wet coats of epoxy, then wet sand that to 600 for the metallic basecoat.  The epoxy will go over the 220 scratches on the Slick Sand and should fill them in.

But on to wet sanding...

Start with a good quality sandpaper (3M) rated for wet or dry.  The panel will be sitting in its final block, which should be 180-220. For wet sanding, P400 grit is the best choice if sanding prior to seal coat.  If you're not doing a sealer and going straight to a [metallic] base, after 400, go up to 600.  Jumping from the 220 to 600 is a large jump and the 600 will take a long time removing the 220 scratches. 

Spray guide coat on the panel.  This helps you to see the scratches you need to remove.  Tear a sheet of paper in thirds and soak it in warm water with a little bit of dish soap for at least 15 minutes.  Get some water and dishsoap in a spray bottle as well.  Using a BLOCK for wet or dry sanding (I like the Durablocks for this purpose) take one of the strips of paper and begin sanding in a cross hatch pattern until the scratches are removed.  Rotate through the different strips frequently and don't let the paper become clogged.  It helps to unclog it by spraying it with the squirt bottle.  Also spray the panel frequently to wash it and keep it wet.  You can use a squeegee to remove the wet dust but I don't have one, so I wipe frequently with a wet paper towel.  Don't overuse the sandpaper; change it frequently so it is always cutting quickly and not just polishing the panel.

Once everything is adequately sanded, wipe it down and blow the panel off with air, then blow it dry.  Inspect closely to see any missed scratches and resand missed areas as needed.

Nothing fancy.  My sanding blocks float in the water with the sandpaper in it somewhere.  Change the water once it starts to get kind of skanky like this.

Wet sanding is nice because the paper lasts longer and there's no dust...but it makes a whole other type of mess.  My guide coated fender is starting to look like a disaster zone while I'm wet sanding the top, but everything comes together once the entire panel is sanded.

The top of the fender in p400.  A few sand-through spots but the fender is straight to the flattened hand.