What causes pinholes? How much acetone do you use?

[Kurt B]

Is it just that the paint is too thick, or is it too thick and not enough pressure? I can't believe I did my original paint without a professional gun/compressor like I have now. When thinned properly it goes on great hardly needing any sanding it appears. However, it's pretty thin that way.

On the other hand, it seems that pinholes are just lurking around the corner, and when I've gotten them all over this new door, I had to use putty spread across the whole door to fill them (new coats won't)...

Best cause/cure for pinholes...?
50/50 acetone/paint-hardener?

[Chuck Moreland]

What gun do you have now and what did you use for the original paint?

[k9handler]

oops...no answer from me.

[Kahuna]

One of several causes of pinholes in paint is the presence of silcone. Body guys hate silicon polish and silicon protectants for that reason.

[Rot 911]

To add to what Kahuna said, could be silicon or you didn't let the primer dry completely. The proper way to correct the problem is to sand the new paint off and start over.

[Kurt B]

Ah....well, I did primer over the old paint. But I didn't sand the old paint completely off. Just sanded it thoroughly with 400 to get imperfections out, then I primered it. Thanks guys...(can't remember the name of the gun--top feed I bought at an automotive paint shop).
For the original paint, I used a crappy gun I got from Home Depot or someplace. Looked OK, but that was after lots of sanding. This time around, I will sand all of it off with 400 (which is easier than 1000 or the like removing orange peel) and do it again until it needs minimal sanding. This appears to be how it's going at this point....
I'm doing the rear fenders, door jambs, ducktail and driver's door at this point with the new gun.

[Chuck Moreland]

Sanding it off with 400? You are one patient guy.

I don't pretend to be an expert but I use 60 to strip paint, then continue with progressively finer grits to get up to a paintable surface.

[CarreraS2]

Yeah, 400 is too fine for removing paint. If you look at the instructions for most paints, 400 is what is called for for the *final* sand before paint (DuPont Chroma 1, for example).

Also, make sure to check the instructions for your paint and do your final sanding with the grit specified. You don't want to use paper that is too fine - the paint won't get a good mechanical grip on the substrate. Use what is called for. Also, be sure to use the catalyst/hardner in the exact amount called for, shoot at the pressure called for, and also add some "fisheye reducer" if applicable. That helps get rid of fisheyes and pinholes.

Pinholes are often caused by too much moisture in your lines. Having a good in-line drier (or two) will help a ton.

[gt3r]

I got some pin holes in my door and I think it was caused by what is called "vapor pop". Basically when the outside temp is too high and the reducer doesn't have enough time to flash off before the top skins over. What was the temp when you sprayed and what reducer did you use?? Just a thought

[john walker's workshop]

wax and grease remover needs to be used when you're done sanding. get an inline toilet paper water filter. use reducer that doesn't dry so fast, and gives the paint time to flow out a bit.

[dean]

You should use silicone and wax remover before you start sanding and what kind of paint are you using that the reducer is acetone?

[lcjjbeav]

Do a search on this painting forum, found it pretty helpful.

http://www.autobodypro.com/wwwboard/wwwboard.shtml

[wcroty]

The term “Pin hole” is generally used with plastic (polyester) body filler.
Craters (fisheye) solvent pops, or blistering would be used to describe paint defects.
There are countless reasons in several steps (system selection, degreasing, sanding, equipment, etc.) that can cause these defects.
If you can send me or post a pic I can help you uncover the problem.


Good luck,
Bryan