bondo over 2k

D

don

I have sprayed 2k & after blocking have found several low spots. Can I apply bondo over 2k?

Don
 
Welcome to the forum!

It's not the best idea, and neither the manufacturer of the 2K nor the plastic filler would recommend it. However, thin applications of finishing glaze ("Bondo" being a generic term for coarse filler, not appropriate for this application) can be applied on 2K that is very well sanded and cured. Most of us have done this at one time or another. I will usually apply some heat with my heat lamp for a good long time to the spots that have been filled to chase away any solvent residue and to keep the primer from tearing away from the substrate. The reason it can do this is because sometimes freshly applied glaze can soften primers that aren't 100% cured.

This is not an approved procedure- Do it at your own risk!
 
scratch it up with 80 grit and apply glazing putty after the primer has cured over nite. you will be fine. you are talking about urethane right?
 
Right......it's SPI 2K over SPI epoxy. Probably 3 more coats of 2K would also fix it.

Don
 
i use 3m platinum plus filler designed to go over sanded paint n primer or bare metal
 
The technical data for 3M Platinum Plus does mention sanded e-coat, but does not mention sanded paint or primer as an approved substrate. So while we use these products outside their design envelope sometimes, it's not helpful to state that 3M wants us to do so. They can't really put sanded finishes on their list of approved substrates because there are too many variables.
 
I've used finishing putty on top of SPI 2k. i get nervous really piling on the primer to fill in big waves. Dont get me wrong, I am a big fan of 2k primers as long as you dont abuse them.
 
Most of the time a finishing putty can be applied over a cured 2K urethane, but it's not without risks, and it shouldn't be done as a normal procedure. If waves large enough to require putty have escaped notice until after 2K is applied, it has to be called an error in judgement that is better off avoided. A lot of the work we do here is not really high end, but we do filler on epoxy and prime and block with epoxy a time or two, applying a bit of finishing putty as needed before going to 2K, just to make sure the work is close enough not to use any more putty.
 
if its really bad and its something that I clearly missed, I will grind down the area and start over.
 
You won't have any problems using filler over sanded urethane primer if the primer is cured well. It's not like applying filler over epoxy within it's recoat window-the exact opposite and shrinkage problems along with adhesion problems are possible if you rush it.
 
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