I'm sure you guys have all encountered this.

For lack of the correct terminology, some contamination gets into the paint and no matter how much you clean, or how much you sand, the paint "checkers" around the parimeter of where you sanded, and it gets bigger and bigger.

I smoothed out a small spot on my cowl with filler and now the top coat of Semi-Flat Black keeps checkering.

The once small spot is getting bigger and bigger.

I've encountered this phenomana before and it's a pain.

Short of sanding a large area down to bare metal I'm considering skim coating the area with a light filler coat to cover the contamination.


Any tricks for this "Checkering" contamination?

Johm,if you can't get it down to bare metal,try some primer before the topcoat.
What brand of semi-flat are you using?

If you can get to it, sand it smooth with 320. If you hit filler, primer it. If you don't, then clearcoat it, let it dry a week or two, then scuff it with 500 and flat black it. If you have to primer it, let the primer dry out o week or two, then sand it with 500 and clearcoat it. After it dries a week or two, then scuff it with 500 and black it.
The clear will seal off the area from the solvents attacking the area and that is what usually makes it do what you describe.
Use light coats of the black to avoid hammering the solvents back onto the area. It may not "flow" like you want, but it won't check up.

What a bear, but I got it.

I just skim coated the entire area with filler, then sanded and top coated with primer, then black.

It worked pretty good.

Until the filler skim coat cracks this Summer :D

We'll see.

Nasty Stuff once it gets in there.