Can I seal then paint over bondo? Or do I have to spray surfacer and let it shrink?

[lemonshindig]

I sprayed a gallon of high-build surfacer on the car. I let it shrink, blocked the whole car, then I used evercoat filler on all of the low spots and sanded them out smooth.

The body should be perfect now. I'd like to spray the primer-sealer and paint today. But I've heard before that if you spray over a filler edge, the filler will expand a little and show a line in the final paint job (even though it's perfectly smooth now). The solution to that, of course, would be to re-spray the entire car with high build surfacer, then let it shrink and sand the lines out.

What do you guys think?

-Matt

[Greg'66 5.0]

I think I read somewhere that the solvents in the paint might cause issues with the body filler. For the piece of mind, I would shoot some primer over the filled areas and block sand those areas - I don't think you need to spray the entire car unless you have that many filled areas. I am about ready to paint my car and with the amount of time I have put into the body, I would not want to risk a blemish in the paint because of something like not repriming over filler. It will keep you from spraying paint today, but do you want to risk a flawed paint job? Block sanding another coat of primer is a small price to pay to get a good paint job. You might be okay with just some sealer - I'd see if the sealer and body filler manufacturer have any recommendations.

I am on my fourth round of priming and block sanding the whole car. Things are looking good now and it's amazing what difference I have seen in each coat of primer. The first time around, I made it down to the epoxy primer quite a bit. On each coat after that, I've got less and less breakthrough to the epoxy. After sanding about 75% of the car on the fourth coat, I only broke through to the epoxy once.

[JohnnyK]

I can't remember what I did, but there are 2 areas on my car that if you look at the correct angle, you can see a line where the filler was (Even though it was perfectly smooth).

But you wouldn't have to spray the whole car.. Just spray those areas with 2k!

[Stevea]

You should spray primer over the bondo and then block again.

[gman]

You need to prime over the filler. No need to do the whole car, then block it off. Then clean clean clean before you paint. The humidity is pretty high right now when you paint I'd be sure to put a disposable water trap on the paint gun.

[lemonshindig]

Originally Posted by gman

You need to prime over the filler. No need to do the whole car, then block it off. Then clean clean clean before you paint. The humidity is pretty high right now when you paint I'd be sure to put a disposable water trap on the paint gun.

My air drying system is absolutely way over the top. The air from the pump goes through an AC condenser from an explorer that has a 22" box fan on it. Then it's dumped into the tank from there. The majority of the water pools up in my tank drain. Then from there, there are 4 8' steel pipes that have two water traps between them, and then one final water trap. And yes, I use a disposable water trap/filter at the end.

Overkill!

[ScottsGT]

Everyone has hit the nail on the head, I just want to add take your time and enjoy this stage. Don't get in a rush, and all will be fine. When I painted mine, I bought hot weather catalyst and had a deadline to beat.
I got it just in time. Next day temps dropped 20 degrees.

[Fullbasement]

Not sure why you're doing so much filler work on top of the primer. It's best to do most of the filler work before shooting the surfacer. No big deal, just advice for next time. Usually once I've blocked the surfacer I'll only have to use a polyester spot filler to catch anything that shows up and I will often shoot right over it. But as everyone has said, it's cheap insurance to get primer over the filler and no reason to do the whole car if there are just a few places.

Using hardened urethane primer reduces a lot of shrinkage issues. I can't believe they still sell lacquer primer where I live. That stuff is almost guaranteed to make sanding scratches show up months later.

[Mustmatt]

I got a lot of information autobody101.com. I would post your question there. I've heard some fillers are better than others. I'm going to be doing what FULLBASEMENT said with a polyester spot filler. My car was just primered the other day and of course I caught some small spots that I want filled.