Im not a hotrodder but seem to come across this forum a lot so id thought id ask here for some advice.
Im having some problem with the paint chipping off, im using PPG DP40 primer and PPG Deltron for the top coat.
The primer seems to be splitting apart as the paint chips have the primer colour on the under side of them and the metal still has a layer of primer on it, I have been spraying some test bits of metal until I get this problem sorted as itís a pain in the backside to sandblast down parts because the paint wont stick.
The total thickness of the paint is about 4mill (0.1mm) measured with a micrometer, I spray on 1-2 layers of primer, 15 or so min later when the primer has gone hard to the touch I spray on 1-2 coats of deltron, the temperature has been pretty cold outside lately but have been warming the parts up with a heater before and after painting to try and sort this problem out but I see no difference with the heater.
Could I be spraying the primer on a little thick?
See picture, paint has been scratched off with a flat head screw driver and plastic pen.
The mils seem awful perfect to me and I do realize the same paint sold overseas may be a different formula then sold in USA.
Only best half guess I can come up with is either you are applying the Deltron to soon over the fresh epoxy (best choice)
Or you are miss-activating the epoxy (even so, unlikely to cause this problem)
Other isolated things that could cause problems like this.
Dried acid film under epoxy.
Cheap wax and grease remover used before epoxy.
Wax and grease remover used and not dry before applying epoxy.
Epoxy applied over metal treatments.
Epoxy applied over rust converters or encapsulates.
If none apply, with what little info we have here I still think paint applied to epoxy to soon.
What may be happening is...... you're putting the top coat on too soon. You should let the epoxy set for at least an hour before top coating. The top of the epoxy is air drying, the middle of the epoxy is not curing. So when the paint chips, the top surface of the air dried epoxy is sticking to the top coat, and the bottom part of the epoxy is sticking to the metal.
The first coat of epoxy is not sticking to the second coat of epoxy.
what grit are you sanding the primer with? Also how long did you let it flash, and how many coats of base did you put on and what was it's flash time?
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