The Stovebolt Site Forums The Shop Area Paint and Body Shop Newbie Primer Questions

I tried something a little different today. The results were not good, and now I'm scratching my head wondering what went wrong.

Normally, when I do body work, I apply a 2-part epoxy primer directly to blasted metal, then I apply filler, then I block sand it smooth, then I apply more epoxy primer. I repeat this process until I'm happy with the surface. This method has worked well for me, but usually requires many repetitions before I'm satisfied with the surface.

I tried to save some time today by using a high-build polyester primer between coats of 2-part epoxy. When I applied the final coat of epoxy over the high-build, it dried with thousands of tiny blisters on the surface. I will need to sand it all off and start over. :mad:

So my general question is this... Are some primers incompatible with others or was this operator error?? For what it's worth, the temperature at paint time was about 95F with low humidity. I applied the 2k primer about 6 hours after the high-build primer. Maybe I didn't wait long enough between coats?? What went wrong?

My experience is do not change primers mid stream. I learned the hard way. It sounds as though your having the same kinds of trouble. There are primers which are not compatible with each other. Sand it down and start over. :>(

I would check the technical info on both primers and see what can go over what. Epoxy primer is basicly for corrosion protection under everything.
High build is for final blocking before paint.
Check the technical info for the peticular brand that you are using to see what you can & can not do with it.

Are your parts under shelter after you painted them? Being in the same area I know our air temps have been well over 100 degrees and if the parts dry in the sun you can cook on them by late morning. I have had a similar but far less severe effect on my epoxy painted parts left in the sun (I have no other easy options). I am using PPG epoxy on bare metal and get a few tiny blisters show up hours after painting. Wiping my hand across them knocks off the top and there is still epoxy covering the metal below. I thought it might be due to the incredible heat that builds up in the sun but I admit I am not very knowledgeable about paint or painting.

Chuck

Yep, it was the heat. I was working inside the garage, but it was well over 100 degrees that day. The paint shop guys say it happens at those temperatures. Solvents in the epoxy can't escape fast enough before the surface of the paint hardens. The result is blistering.

I sanded the top coat off and waited for the temperature to drop down to 80. I used the same paint and the same equipment again, and this time it turned out okay.

That's it exactly, the basecoat primer solvents were trapped by the epoxy topcoat and caused the bubbling you saw.

Hank

Are you sure it was the heat? If that was the case, the what would happen if you were in a Baking booth with the curing cycle on? Most of the Epoxies the I have used recommend that they be forced dried for best results.

Good point. I don't know. The guy at the paint shop said this happens all the time in hot temperatures, but I never thought about the baking booth.