Filler over SPI epoxy AFTER 30 days

MAKZ06

Newbie
I need some clarification on applying filler over SPI epoxy. I‘m only able to work on my projects typically every other month because we don‘t live full time where I have my vehicles.
I understand I have a 7 day window to apply filler over the epoxy without sanding or scuffing. However, I’m confused after reading some other posts regarding when filler can be applied over older SPI epoxy even after its been sanded.
I sprayed my last coat of Epoxy back in May. I’m once again block sanding the panels and have found additional low spots that need small amounts of filler. Can I apply filler directly over the epoxy which is freshly sanded? Or do I really have to shoot another fresh coat of epoxy before I can proceed? It’s so difficult and time consuming for me to get setup again to paint...
Another question. What will happen if I already applied filler (last year) over sanded epoxy that had been sprayed several months before? It’s now sandwiched in between the last coat of epoxy... Will it fail?
 

MAKZ06

Newbie
After 30 days, you must re-epoxy for proper adhesion.
Well that is unfortunate. So am I looking at potential catastrophic failure with what I had already filled or Is it more akin to applying filler over bare metal and is just not as good as to freshly sprayed epoxy?
what I’ve already done had been very thin layers applied to epoxy which had been sprayed many months or more prior,the old epoxy had first been sanded with 80grit, and then fresh epoxy went over that.
wow. I may shoot myself if I have to take it all the way back down to bare metal and start over.
 

elwood

Registered Users
I could be wrong. If so someone correct my thinking. I don't think Barry is saying it has to be taken down to bare metal again. Clean and sand the existing epoxy, then put new epoxy over the old epoxy and keep on trucking. I've done that several times and not had any problems. Like John Long said Barry would not give you any advice if it wasn't correct.
 

MAKZ06

Newbie
I could be wrong. If so someone correct my thinking. I don't think Barry is saying it has to be taken down to bare metal again. Clean and sand the existing epoxy, then put new epoxy over the old epoxy and keep on trucking. I've done that several times and not had any problems. Like John Long said Barry would not give you any advice if it wasn't correct.
Yeah, that I can do. However, I previously applied filler over sanded epoxy that was cured for several months.... I did not respray epoxy before applying the filler because I didn’t know that was necessary. Missed it somewhere in the documentation. I thought I just needed to sand the epoxy before reapplying filler or more epoxy if it was outside the recoat window...
 

MAKZ06

Newbie
I’ve done that too - as long as you sanded the epoxy with 80 grit you should be ok - filler likes 80 grit - BEST practice is fresh epoxy though
That makes me feel better. Definitely sanded with 80 prior to applying the filler. I’ve been sick to my stomach thinking about it all day...
 

texasking

Active Member
I believe what Barry was stating was that after 30 days you lose all chemical adhesion, and are then relying on mechanical adhesion only, which may not be sufficient. Sand an area where you applied filler over the old epoxy and see if it feathers out, or try to remove it with a razor blade. I believe it will be easy to tell if it is "stuck" or not.
 

MAKZ06

Newbie
It definitely feathered-out and appeared to be behaving as I expected. Most that I had applied was to cover imperfections around patch welded areas and was under 1/16” thick. I had carefully made sure all the low spots and surrounding epoxy had been covered good with 80 grit scratches. None of the filler lifted or left a transition lip you could feel after sanding. It even got sanded again months later before the next layer of epoxy was sprayed over it, and it maintained the feathered edge.
thanks for the advice. I know better now how to do it correctly.
 
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