Originally posted by paintman1:
<strong>etch primer should be used only for bare metal. It has an acid in it that does a couple of things. Helps it adhere to the bare metal and helps to get rid of rust that has started(normally a few seconds after metal is exposed to air rust has already started) and to prevent it from starting. The other guys are right and that you must have the right temperature, surface must be clean and the product must be mixed correctly. As far as a primer sealer, I would use a primer surfacer which is typical primer for filling in bodywork. If the car has other layers of paint the primer you are putting on could be reacting with those layers and cause the primer to "lift". This can look like small shrinking. You might have to sand that all out and apply the primer in lighter coats or strip off all the layers of paint.</strong><hr></blockquote>
I am betting you hit the name on the head. As soon as I read it that sounded like exactly what is going on. I have used self etching to cover a small breakthrough to bare metal when finish sanding primer and have seen it react with old paint at the feather area of the breakthrough.