Dealing with existing POR15

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PostPosted: Mon Dec 04, 2023 3:46 pm
I've cut out the rust and I'm repairing with some patch panels on a friends car, he has previously cleaned up the metal in the wheel wells and painted with POR15.
I'd rather not scrape all of his work off but I normally prime bare metal with 2k epoxy primer.
Are the two compatible, can I get away with sanding the por15 to roughen it up then spray all with the epoxy primer?

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PostPosted: Mon Dec 04, 2023 6:47 pm
Questions like this should never be asked on a forum. For a start, different epoxies have different substrate requirements. Then you haven't identified which epoxy you're using. You'll get 10 different replies which are likely to be all wrong and, when it all goes south we'll be blamed for giving you poor advice.

Refer to your TDS. I know it sounds like RTFM but getting this right is critical for anything that goes over the top and long term performance. If the TDS is not clear then call the manufacturer and speak to their Technical guys.

Interesting repair. :rolleyes:

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PostPosted: Mon Dec 04, 2023 7:32 pm
The problem with POOR15 that I have read about is that isn't flexible like epoxy is. What that means is it dries hard and then doesn't move with the metal when it stretches from heat or shrinks from cold temperatures. Eventually it will crack and that allows moisture to get under it.

There are quite a few threads on this and different sites detailing the issues with it. I suggest you do some research before making a decision on how to proceed.
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PostPosted: Tue Dec 05, 2023 9:00 am
Anecdotal evidence: I haven't found any substrates I've prepped and shot with epoxy primer (OK, and Tamco), that the epoxy didn't stick to.
And for the most part, Whenever I put another coating over POR-15, or it's variants, I haven't seen any failures. I use undercoat over it a LOT, putting it on when the POR is tacky. I just put Zolatone over it in my own personal project, over a sanded/scuffed finish. On non-critical parts, I've even put primer and paint over it. I've used it as a primer on engines that I can't, (or it's not worth the effort) remove all the rest before paining. While I don't have access to all the cars I've done over the years, the ones I do see, are still looking good.
I do NOT use it on the outside of anything I build, though. I have seen some aggressive solvent paints attack feathered edges of POR.
On your repair, I'd say try to feather it out. If it doesn't feather, and comes off in sheets, remove it all. If it's adhered, go ahead with plans.

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