POR-15 and Bondo

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POR-15 and Bondo

Post by cloudbreakmd on February 24th 2008, 9:33 am

I had some fender lip rust on my car. I scraped all the loose rust away and applied POR15 to seal the remaining rust where the metal still felt solid.

The POR is now dry and hard as a rock. Now I need to bondo it. Anyone here put bondo over POR? Any suggestions on how to prep the surface of the POR before I start using the filler?

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Re: POR-15 and Bondo

Post by Slick on December 23rd 2008, 6:53 pm

From the POR 15 FAQ:

"CAN I USE BODY FILLER OR PUTTY WITH POR-15?
Yes. First paint both sides of the rusted area with POR-15; then use body filler or putty as soon as the POR-15 is dry to the touch."

I didn't see anything about sanding it first, so I'm thinking that if you sand it it will compromise the integrity, or they think you might.

I bet if you apply it generously, and it's dry you might scuff it up a little bit with out breaking the surface and use filler over it. If you break the surface, rust will come back / spread.

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Re: POR-15 and Bondo

Post by ShelbyDodgeImp on April 30th 2009, 12:16 am

That said the rust may come back anyway, I've had a lot of problems with POR working for more than a couple years.

My personal experience and pics are here:
http://www.cardomain.com/ride/3072884/5

Seems some people swear by POR, some people swear it doesn't do a thing. My experience was very bad, either it would peel off (exposing bare metal), or it would simply rust threw the POR.

I am inclined to believe my car would be rust free still had I left the stock sheet metal alone, I took the rockers, floor boards, and bottom few inches of the doors, quarterpanels, and fenders down to bare metal to apply POR thinking it would be great preventative work. In the end, the areas I didn't POR held up far better than the areas I POR'd!

To use some examples, I did my rear axle in POR, this is not a part that was painted nonetheless I used their stripper followed by marine clean followed by metal ready. Not a part in the sun, so I didn't top coat it (topcoating is optional for stuff not in direct sunlight)



2 years later, it was rusting threw the POR:



Rocker panels? In two years they went from rust free to this:



And that's with 1-3 coats silver, followed by 1-3 coats black hardnose topcoat.

I am inclined to conclude that nothing beats cutting out and welding in new metal.

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Re: POR-15 and Bondo

Post by ShelbyDodgeImp on April 30th 2009, 12:19 am

Oh, and I forgot to add- some people are claiming on some forums that you should sand rusty areas before applying POR, and the POR should never overlap stock paint/primer if you want it to stick.

I have no idea if that's true, but back in 2003ish and 2005, when I played with POR- the instructions specifically said to the effect that no sanding of rusty areas was needed, you just had to brush off any lose rust particles.

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Re: POR-15 and Bondo

Post by tpirsig on May 26th 2009, 12:07 am

Just to add a comment on this -- I've used POR for years and surprised recently that some rusted through quickly, which hadn't happened before. Then I surmised that it was because I'd used the silver, the black was always fine. So for some reason I had trouble with the silver, and I see you used the silver first.

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Re: POR-15 and Bondo

Post by retired plumber on May 26th 2009, 12:56 am

I would think it would be common sense to get rid of as much rust as possible before applying POR15 or anything like that. I don't care what the can says. This is one of the few times I go against directions. I have not used it but several people I know have and love it but they first cleaned the piece up the best they could. POR took care of the pits and small places they could't get to but DON'T expect it to fix the large scaley places where you can peel it off with your fingers.
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Re: POR-15 and Bondo

Post by tpirsig on May 27th 2009, 3:26 pm

I agree 100%. I first remove what I can mechanically, then with acid, then use POR. Early-on I tried some on loosely-scraped metal and it failed after a year.

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