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Discussion Starter #1 (Edited)
hello kinda new here and i have kind of an odd question. what can i use to paint over undercoating on my 69? i have thinned down fiberized roofing tar for undercoating on the inside of the panels on my 69. sounds kind of redneckish but i like it and it's held up well for a few years now but- i tried to paint over it (inside fender panels at trunk area) useing a rattle can (krylon or rustoloem brand etc) and it's good for a day or two then the paint cracks. doesn't crack the undercoat clear to the panel the paint just splits and looks like crap. my body guy painted over some of it in areas with his paint gun and what he painted looks fine. i would ask him what to do but unfortunately he died a few years ago. i will also be doing the inside of the fenders etc as i think this will keep the undercoat from drying out over time.

any help from the chemistry majors out there would be appreciated.
thanks.
 

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you need use a water born/based primer sealer first...

the solvent in the paint will loosen soften dissolve the undercoating you have and paint will crack when dry....thats why you need to put a barrier/sealer coat first...;)
 

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you can try some rattle can undercoating and spray over it. That stuff is close to smooth when dry.
 
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