I am helping my buddy with his 70 Olds restoration and need some wisdom.
The body has been blasted and put in DP90 Epoxy sealer. We are currently
working on rust repair and metal work, the car had it's fair share.
By the time we start spreading filler the sealer will have been on there for close
to a year, long past the recoat window.
My question is can we just scuff sealer before applying filler or will we need to
scuff and re-apply sealer before filler?

I

Think I answered my own question, according to the tech sheet it will need to be cleaned,
scuffed, re-cleaned and then another coat of epoxy sealer.

you should be able to put filler over sanded epoxy, i would use 80grit

The recoat window is the concern, I've heard two opinions on this.

After doing some research it seems for "maximum" adhesion, if the sealer is past its 7day
recoat window then cleaning, scuffing and re-shooting is recommended before applying next step, again for "maximum" adhesion.

But it seems the optional method per PPG is, If the sealer is past its 7day recoat window
just clean, scuff and apply next step.

I guess what people will have to decide on is how concerned are they about "maximum" adhesion. I am by no means experienced enough to know..lol

ether way will work just fine, its all up to you. if you do recoat the epoxy you shouldn't just rub around on it with a scratch pad and spray over it, as that word scuff kinda worries. me you'll need to get a good profile on it for the maximum adhesion. you have a couple ways you can go here. spot sand the epoxy and do your filler work. then sand the complete body and coat with epoxy or hi build primer. or sand the complete body and recoat with epoxy and do the filler work and get hi build or what ever on before your out of the window. the last might be pushing you a little if you have a lot of body work no mater what you do your going to have to sand all the old epoxy.
if you really want to recoat the epoxy with epoxy I would just sand the repair areas and recoat them. then do my filler work then sand the complete and recoat with what ever.
best way would be sand with 80 grit and apply filler much simpler.
Jay D.

Thanks for the advise badsix, I'll mention it to my buddy and see what way he wants to go.
I think the last option of sanding/recoating repair areas then filler work, followed by a
overall sanding before primer sounds like a good plan.