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Discussion Starter #1
About 3 months ago I stripped the paint off my bumper located all the visible hairline cracks "v"d and feathered them out and filled them in with a 3M 2 part flexible bumper repair that I have been using for years, all of these repairs are fine. The dozens of tiny hairline cracks that you cant see in the factory endura rubber seemed to also have been filled in while priming the bumper with SEM 39134 FLEXIBLE PRIMER SURFACER but now that I am ready to paint I can see close to a hundred hairline cracks after the primer had aged and shrunk.These cracks go right down to the rubber when you try to sand them out . Can anyone recommend a surface that I can use over this primer that is forgiving enough to fill in these hairline cracks without shrinking and cracking again before I lay paint . My intention was to also mix some PPG DX814 universal flex agent into the top coat .
 

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I think the mistake was using primer surfacer. Even the "flex" kind isn't flexible enough. I made almost the same mistake prepping my brand new (that I bought 20 years ago and had been saving) Endura bumper. I scuffed it, shot it with top quality epoxy primer, then put primer surfacer over that. Crack city - and I wound up paying to have all the primer/surfacer glass beaded off of it. Then I went back with the epoxy primer, then direct to base/clear over that. That's what I should have done to start with.

Bear
 

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Discussion Starter #4 (Edited)
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The primers not cracking from being stressed it literally has been sitting on a shelve for months until I went to paint it the other day. All the Google searches only tell you how to fill in gouges, etc.. the areas that I repaired with a skim coat of 2 part repair are all ok its the other 70% of the bumper that I primed with the surfacer that dozens of tiny cracks appeared , I could see them in the endura rubber before I primed thinking that the primer would just cover and it did until I looked at it a few months later. So I my question is what other filler/primers have been used with good results
 

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So I my question is what other filler/primer would has been used with good results
I used Southern Polyurethanes Gray Epoxy Primer over the bare, scuffed bumper and followed that directly with base (PPG DBC9700 black) and clear (Southern Polyurethanes Universal Clear). The paint is now 4 years old, and no cracks.

Bear
 
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