Wurth - what did I do wrong?
 

Last August when I first got my car one of the first projects I did was remove the gas tank and restore it. On the outside I stripped the entire tank to bare metal and covered with Wurth SKS Gray from a spray can - not a gun. I didn't prime the tank the Wurth went right on the metal. That has held up just fine until:

I am currently disassembling the entire front end for color change and rebuild. When I removed the plug in the bottom of the gas tank a little gas got on the outside of the tank. The gas instantly took off the stone guard down to the metal. Anywhere the gas touched it the stone guard would just rub right off. It is supposed to be resistant to gas.

Why? Is it because of a lack of primer (I actually may have primed - just can't remember and it's not in any of my pics)? I didn't paint the stone guard - is that the problem? Is it because I used the aerosol can Wurth?

Any thoughts? As always thanks for the input.

I've had the same problem with water based Wurth SKS. Gasoline melts it instantly. Mine was applied with a Schutz gun and compressor.

Joe

Paint needs to be applied to seal it off.

I may be wrong but that stuff is not meant to stand up to solvents.

I agree, and this runs counter to the general belief the water based sks is equivalent to the material originally used by the factory. I've still got a sample of the original material that I stripped from my tank. It was not painted, and was not affected by gasoline.

Sounds good- I'll paint it next time - at least I know how to easily strip the rest of the stone guard now.

MOST Wurth stuff is good quality but not all. On the upside, they do stand behind what hey sell. Tell he Wurth rep an he will replace it and make I up to you.

Agree it needs a final coat of paint, either in the color or a flat clear for chemical protection.

I ended up laying two coats of satin black over the entire underside of my car during the resto, helps to keep it clean and gives chemical resistance.

You probably need a 2 part catalyzed paint. Based on what I've learned from a recent motorcycle restoration, any normal spray paint will run or bubble if you get gas on it. You can put color on with a spray can, but if you think it is going to get gas on it you need to protect it with a catalyzed 2 part clear. Check out spraymax 2k, you can get it at a good auto paint supply store or online from Eastwood. Or you can take the tank to an autobody shop and have them spray it. The 2 part stuff is dangerous, you need a good respirator.

Thanks macond I just bought some HVLP guns and a fresh air respirator so I have been itching to use them.

+1

The stuff will melt your lung's alveoli.

Minimum for a small job, charcoal mask with fresh filters and large fan pulling fumes out thru half opened garage door with fresh air coming in the back door or window. Even with this coverage OSHA would still say no.

Good to know that it needs a top coat. I'm about to do the same on my tank and have the water-based black wurth undercoating for a schutz gun. Used it on the entire bottom of my car. Now you have me wondering if I should top coat that too. Would've been easier to do on the rotisserie before all the suspension was installed...

If you are not really trying to replicate the factory appearance you can just do like I did and POR15 the thing. They make a sealant kit for the interior, and you can just use the regular (in whatever color) on the exterior. BTW I highly recommend the sealant kit!

Never considered POR15 for the outside - I looked at the sealant kit but I have the plastic swirl pot in my tank and that seams to be a no no.

I was also concerned about the swirl pot--however my leaks around the seams where the tank halves come together and rust issue at the top of the tank where condensation had done its damage led me to believe that the risk was worth taking. The sealant kit is not terribly dangerous in my opinion--you put it in, swish it around, rotate the tank to allow it to sit in the seams, the drain the residual. The worst thing that could happen is it clogs the intake or return ports. I highly recommend using a small section of cotton rope to run through the ports while you do all this as to ensure that you don't have sealant get in those areas and clog them--this stuff dries HARD!

The purpose of the swirl pot is static--that is it is design to act as a funnel when you are low on fuel. In my analysis, I do no believe its function to be impaired if covered with sealant material.

Good to know it worked for you - the warnings I read had to do with adherence of the POR 15 to the plastic. It was all theoretical though - I coundn't find anyone who had done it. The concern was that over time it might start flaking off. I had mild rust in the tank. I started with electrolysis to clean it but it was too slow for me so I used muriatic acid followed by phosphoric acid then rinsed and filled with gas.

Thanks for bringing this up! After researching what others have used I painted my tank with Wurth SKS stoneguard and must have missed where I should have painted over it with clear or similar. It is already installed on the car so hopefully I can fix this without ruining the finish that is already on there.

So - can I spray color directly on top of the Wurth or does it need some type of primer first? Can anyone recommend a gray that looks close to stock? I'd like to spray it with my new paint gun to start getting some experience.

Since no one else is making a suggestion, I'd say go ahead and spray right over it. I just looked on the Wurth website, it indicates that it is indeed paintable. If you are just going to "rattle can it," I'd use an enamel over an acrylic. These are just my thoughts, not speaking with any authority.