Hi, Exactly which PPG paint products are you referring to? I have noticed a certain proneness to chipping with the OMNI MTK acrylic urethane. I have also noted that the OEM paint on my Toyota truck is also prone to chipping. I believe that's an acrylic urethane basecoat/clearcoat. The second time I've noticed fairly easy chipping with the MTK was about two weeks ago when I dropped my AC-B gas cap on a concrete floor. Height of drop was about 5 ft. Here's a picture of one of the two chip spots resulting from that:
I am a little surprised this time that the chip went all the way to the sandblasted surface. Previous chipping that I have noticed has been at the color/primer interface. In all cases, the paint system was as follows: 1. Sandblasted surface 2. Two coats of PPG OMNI MP170 epoxy primer 3. Three coats of PPG OMNI MTK acrylic urethane single stage color within the epoxy window 4. Three coats of PPG OMNI MC161 acrylic urethane clear within the color window I've been advised that the chipping is a characteristic of the low-end urethanes. If that's true I am not sure that you can do much of anything without changing products, assuming you are talking an "economy" urethane. My experience in the past has been with hardened acylic enamels (PPG's Delstar and DuPont's Centari). I've never noticed a similar chipping problem with either of them. I think it may be because they are not as hard (and brittle) a paint film as the urethane is. Then again I don't think I've ever had the exact same conditions (like dropping a gas cap on concrete) with those paints either. I plan on trying some of PPG's premium single stage urethane, Concept, this spring when the weather gets warm. That is significantly more expensive than the MTK so I guess I may find out if a more premium product will improve the chip resistance. If it doesn't, I may consider moving back to Centari, assuming I can still get it locally. The Delstar is no longer available in my area - a shame. I really like the MTK though. It's fade and chemical (at least gasoline ond oils) resistance are both very good. Plus it is not that expensive. The only downside that I have noticed with it is this chipping thing. It doesn't happen with only a "light" hit though - at least for me. I "tunked" a fender the other day with a wrench and there was no chipping problem. The fender was painted the same way as the gas cap. The previous chip problem on my tractor was caused by the fairly heavy bearing force of a hand crank rubbing against the sheet metal opening in the front radiator shroud. I don't know what type of paint is used on modern tractors but if you are talking factory paint jobs from the '40s, or '50s you are likely talking an alkyd (synthetic) enamel. I certainly would not call that more "durable" than a hardened acrylic enamel or a urethane. I suspect it would be less likely to chip as easily though, since it is a relatively soft paint in comparison. However, the fade and chemical resistance is not as good as a urethane, or even a hardened acylic enamel. Rod
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