Last summer in the Florida heat we were doing our body work. and trying to get my car up to par to paint it. We were having issues with the primer and the heat and of the metal. Now we were paying a friend to finish up the rest of the work and do the top coat. He has been working very hard on it part time since Christmas. He has been letting it bake in the sun and my primer has been developing cracks. He then sprayed on a darker top coat to help it absorb more heat. I am glad he found this before we painted it, but it is still upsetting me that I screwed up. What causes this? What did we do wrong as novices to cause this. We tried to follow all the rules but obviously we did something wrong.

Here are some pictures.
Passenger quarter:

What products were used?

& what year is the mustang?

I have used all Matrix products, and 65!

Here's my opinion.
The primer was sprayed over filler, correct?
My guess is that the filler wasn't completely cured when you sprayed the primer, which was sprayed too wet, it cracked.
Or
The primer was thick and not dried when it was put out in the hot sun, causing it to crack.

Whats under the sprayable stuff? metal or mud?

There is a mix, we started with an matrix acid etch primer, then some evercoat where it was needed. and then the matrix 2k high build primer. When we were spraying during the summer the high build was almost drying before it even got to the car and came out with an un-smooth surface. So we would sand it down till it was smooth. Since we were sanding away so much of it we were putting it on pretty heavy. The filler sat for a little while in a hot florida garage before the primer when over it.

Thank you for you guy's help. I appreciate it! This is my first project and its been about 5 years. Now that I am in college and have a good job(system admin for one of the departments) i don't get to go home to work on it as much

If I understand your last post, you put filler directly over acid etch primer? I don't know if that would cause the primer to crack, but that is not supposed to be a good thing.

I think the primer was layed on too thick. And with the heat, the solvent evaporated too quickly, thus the primer shrank and cracked. Sounds like with the primer drying before it hit the surface was over reduced.

I've seen primer used to fill scratches and blimishes. Like any other paint, you have to put it on in thin coats and let it flash.

kstang wrote:matrix acid etch primer, then some evercoat

DING! We have a WINNAH!!
That's the cause right there, the mud won't kick off fully where it's in contact with the acid etch and as it's not cured it expands and contracts more with the temp changes. Then that telegraphs thru the primers etc and the result is what you've ended up with.

ZRX61 wrote:

kstang wrote:matrix acid etch primer, then some evercoat

DING! We have a WINNAH!!
That's the cause right there, the mud won't kick off fully where it's in contact with the acid etch and as it's not cured it expands and contracts more with the temp changes. Then that telegraphs thru the primers etc and the result is what you've ended up with.

I am not arguing with you, but most of those spots are where there was no filler. Could there be any other cause?