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Hi Dale, You may not be doing anything wrong at all. I have used PPG epoxy primer and both acrylic enamel w/hardener and acrylic urethane single stage as topcoats. I have noticed more chipping of the film with the urethane. I think the urethane seems more prone to chip because it is a harder, more brittle and less flexible film than the hardened AE. I am not positive of that but it seems a reasonable explanation. I have also noticed, somewhat to my surprise, that the OEM BC/CC urethane on my pickup truck seems quite prone to chipping when I installed a bed-mounted toolbox. Both the OEM paint on my truck and the SS urethane on one of my tractors I painted, chipped at the color-primer interface. The place on my truck was the bed lip where the tool box J-bolts clamp on. The place(s) on my tractor was at several bolt heads during assembly plus where the hand crank sometimes rubs against the front radiator shroud. I am always careful to keep within the time window for topcoating the epoxy so I can't blame that. If you exceeded the time window, you would not get the best adhesion of the topcoat to the primer unless you scuff sanded and reapplied the epoxy before the topcoat. Other than that, you probably did nothing wrong. I have concluded, rightly or wrongly, that increased chipping is a downside of urethane paint films. I have thought about using flex additive (MX193 in PPG OMNI) to try and minimize the tendency to chip but have not yet tried it. I have heard mixed views on whether that does any good at all after full cure of the film. I would also like to hear additional thoughts on the subject. If this is a common occurrence, I may decide to go back to AE w/hardener :o).  Rod
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