I have used DPLF for years and even though I have recently changed to SPI epoxy which I much prefer I do not think the PPG is a bad product. I am in the middle of repairing some bubbles in the crease of my 36 Ford roadster door that was painted 4 years ago. The door was stripped to bare metal, primed with DPLF, primed with K36, sealed with DPLF and painted with Concept? In order to determine why it failed I took a razor blade to it yesterday to determine at what level it failed.
I was amazed to find the bubbles go all the way to bare metal. All layers of paint have good adhesion. To my surprise the metal is perfectly clean and shiny.......Too shiny. THIS FAILURE IS MY FAULT. When I stripped this door I treated it with RustMort and wire brushed the crease area. There is no doubt The failure is the result of me failing to neutralize the acid and/or polishing the metal to the point the paint had no tooth to bond to. Add to this it was painted in a very cool shop.
The point I am trying to make is these modern materials work by chemical reactions and depend on the proper procedures being followed. That includes temperature, preparation, Mixing ratios etc, etc. Rarely is a failure due to the product being bad even though I wish I could blame it on the paint.