I have been planning to use POR15 on the entire underside of my car. That is up unitl about 2 days ago. About a month ago we painted a couple of small areas on the tub. One area over bare metal and one area over existing paint. The existing paint area was scuffed, marine cleaned and metal ready was applied and then the POR15. I decided to strip part of the POR in the 2 areas just to see how well it had adhered. The POR over the bare metal had good adhesion. The POR over the prepped paint did not. Once I started stripping the POR it started peeling off in strips 1/2" - 2" long. Wasn't expecting that!!!

I had called the POR 15 place about 2 months ago and spoke to them about painting the POR15 over existing paint/undercoating. Got a standard line of its designed to be most effective on bare properly prepped metal. They said it may adhere well to paint/undercoating, it may not.

My experience so far is that it does not stick to the existing paint on the bottom of the tub.

Has anyone else used POR15 over existing original paint on there 914 with success?

I am currently looking at using a Sherwin Williams Epoxy Primer on the tub instead of the POR15. This was a recommendation from a local restoration shop that has used this product successfully on several cars. Anyone in this group used an Epoxy Primer?

TIA

It needs to be to rust or prepped metal. It is not designed to chemically bond to paint or primer.

Your results are what is expected.

that is correct, BUT

he said he used metal ready on the surface first. which "should" work because the por-15 will adhere good onto the metal-ready UNLESS

you didn't wash off the metal ready with water first, before you painted it with por-15!

i had the same problem on my car where i used metal-ready and didn't wash off excess before painting with por-15. it would just come off in flakes and not bond.

if you wash off the excess metal-ready first, it'll stick ...

Andy <-- who did the complete interior with MR/POR-15!

Andy - Did you strip the paint off all surfaces before applying the por15? Or, did you leave some paint and put the por15 over it?

Today I stripped off the rest of the por15 that was applied to the paint covered surface. Some of it had good adhesion to the paint, but most of it did not. There were 2 scratches in the painted area that was covered with the por15. The por15 bonded very strongly to the scratched, lightly rusted area - just like it is supposed to.

Would you guys suggest POR15 for underside of the chassis and the wheel wells?

Andy, did you repaint the roll bars after the por 15? or what about that one month of sun thing with por 15?

Andrew

Also... metal ready ISN"T going to prep the surface of paint....

Even if you apply Metal Ready over paint, it still isn't going to stick well.

Based on what I saw with the lack of adhesion - No. Unless someone can say that they have done this successfully. And, it has held up for several years.

Edit - If you strip ALL of the paint first it should work.

nope, only removed paint where i had surface rust. cleaned it off with brake cleaner which roughs up the surface, then applied Metal Ready (mostly around the rusted areas), then washed that off, then painted POR-15 ...

Andy

nope, that's just por15. the black doesn't seem to be affected. i have seen the silver turn greenish/yellowish ( )

Andy

it did for me?

here's a link with lots of pictures, so you can see what i did:

http://www.sirandy.com/projects/cars/20020520.asp

Looks like you sprayed it. Was it really thick?

Andrew

the spray coat was fine (and thin) but it got so dirty in the following YEAR in the shop that i brushed on a second coat of por15 before putting the car back together.

i just couldn't get the 1st coat clean
Andy

I have used POR-15 on 3 914's. I have only used it after stripping completly down to metal. Only used it in areas that are not visual, e.g. front and rear trunk, engine compartment, floors, longs, windshield channel,weather stripping channels, light buckets etc.... Stuff has worked great.

On the engine compartment and some other places, I used the POR-15 tie-coat primer on top of POR-15 so I could more easily paint another color, or the car color/paint itself on top. This also seemed to work well.

On the underside of the car, I can't imagine trying to strip all of that tar based stuff off myself... maybe media blasting by some outfit... and after that I would not put on POR-15... I would probably primer and paint to the body color or just black if I went that far.

To repair smaller spots on the underside of the car, I stripped the spots and coated with some Henry's roofing compound, which seemed to match the consistency and look of the stuff the factory put on... and it was cheap, it stuck and is it is waterproof! Probably burns like the factory stuff too... every light some of that factory coating off while welding... I have.

- Dave