Gas Tank Recoating - How do I proceed?

[chaw704352]

I have some spot rust on the underside of my gas tank where some of the undercoating scraped off over time. My plan is to
- wire brush off the undercoating around all the rust spots,
- remove the rust with wire brush,
- POR 15 these spots and then
- recoat with Wurth SKS Stoneguard (Gray)

The Gray with the new SKS is a completely different color than the current undercoating. Do I still coat the entire gas tank with new stone guard, or do I spot treat and then paint the gas tank a single color?

[chuckr]

I just did my tank. Be sure to check the seam around the middle of the tank for rust.Mine had some rust there. I did my hole tank with 3M rubberized undercoating.That Stoneguard should be better, do the whole thing !

[chaw704352]

Did you strip all of the undercoating off of the entire tank before you recoated, or did you just do the rusted out spots?

[chuckr]

Just the rust. I stripped to bare metal, treated and put the 3M on just the rust spots. Next day sprayed the 3M on entire tank

[chaw704352]

OK, I stripped the rusty spots (plus a lot more, but not all) to metal, POR-15'd the spots, then used the SKS Stone Guard. it looked great (love the Wurth gun).

However....the SKS Stone Guard did not adhere to the POR 15. So I got to spend this morning stripping everything back down. I've POR 15'd again and will then test some self-etching primer to see if I can get that to stick.

No fun doing it twice.

Does anyone have recommendations on SKS over POR 15?

[Classic]

If you spray Por's primer coat in the recommended window then you SKS all will be good. Or you can really scuff and i'm talking 80 grit the Por the SKS should stick. I went for the first option, and all good so far

[chaw704352]

I tested some duplicolor etching primer on top of POR 15 and then tested with some SKS. It stick great! though I did use a brush to test the SKS and didn't spray with the gun (don't know if that matters).

I'm going to coat the entire tank with the etching primer, scuff it a little with 150 grit and then recoat with SKS.

I sure don't want to do this thing a third time. Stripping SKS off with a wire brush is not a fun task. Not as bad as getting the original 1/8" of undercoating off, but still not a fun task.

Unfortunately, the temperature just dropped about 30 degrees in Dallas over the last day, so I may wait until tomorrow.

[chaw704352]

Scratch all of that.

The SKS stuck great to the Duplicolor primer, but the primer wouldn't stick to the POR (I could pull off large rubbery strips of SKS using my fingers). Not cool!

I stripped it all down again (third time is a charm). This time I put Eastwood Chassis Black Primer over the whole tank (including over the POR 15). After 24 hours I tested it with my fingernail and it scrapes off (I was not happy).

What I learned is that SKS is great, but POR 15 should be used with caution.

However, the next day (48 hours), it was solid as a rock and sticks like chewing gum off the street to your flip flop in summer.

Since I'm using some POR 15 on a few troubled areas on my car underneath (and then coating with SKS), this was actually a valuable learning experience. Painful, but valuable.

[Evans, Marv]

You should get it it to stick to the POR-15 if you either scuff it like Classic said or apply over it before it totally sets up. Once the POR-15 cures, it's like powder coating. Also you could call them for advice.

[chaw704352]

Thanks,

I've got it figured out for now. I spoke with some paint jobbers about it.

On one go-round, I scuffed the crap out of it with 150 grit and then coated with SKS. It just wasn't enough to create any good bond for the SKS. Other people had success with this, but not me.

The paint jobber who said there are basically two guaranteed ways 1) use POR's Tie Coat, or 2) a decent epoxy primer. Since the Tie Coat was on backorder, I went with #2.

Again, others had luck with the scuff method, but it wasn't working for me. My guess is that the 3m undercoating might bond much better to POR15.

[D911SC]

Use a 3M red pad or similar and remove all the gloss off the POR15. Clean the surface (wax/grease remover) and then apply their Tie Coat or Upol's Acid 8. After this you should be fine to apply the SKS.

I did exactly the same thing on the underside of my car with excellent results.

Also, make sure your SKS is not past its Use By Date.

Good luck with it.