How to strip rubberized undercoat???

[Andy Somogyi]

I’ve been trying to (partially) strip the undercoat because I want to repaint inside the trunk and gas tank.

I managed to get all the undercoat off the gas tank with several gallons MEK based stripper and wire wheels and a massive amount of work.

I’m trying to strip the undercoat off the car, but keep the galvanized zinc, so I can’t use a wire wheel.

What takes this stuff off??!?! It’s impossible!

I don’t want to use a torch because I want to keep the paint on the opposite side intact. Can’t use an acid because that will take the zinc off.

What kind of solvent will break this stuff up???


Trying to keep the stripper covered, maybe this might work better. The problem with methyl ethyl ketone or methyl chloride or most of these solvents is heat is vaporization is effectively zero, so they just evaporate right away.

This rubberized undercoating is some seriously though stuff.

This stuff is miserable trying to remove it.

I want to stay solvent based because I don’t want to harm the zinc galvanizing.

I know HCL softens this undercoat up, but yeah, that’ll take the galvanizing right off. Don’t want to use heat because I don’t want to burn off the stuff on opposite side.

Anyone at least know what’s the chemical makeup of this undercoat, is it a polyurethane rubber?




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[kwah]

I've seen dry ice blasting remove that stuff. Check out cryo-werks website. Not near you but will give you an idea. No affiliation with the company.

Cryo Werks – San Diego

[jamesjedi]

I used a wire wheel. It is a huge effort and a giant mess. I remover all the undecoat with the wheel. I will never do it again.

[Andy Somogyi]

Originally Posted by jamesjedi

I used a wire wheel. It is a huge effort and a giant mess. I remover all the undecoat with the wheel. I will never do it again.

Wire wheel and stripper worked OK on the tank, but I don’t want to mess up the zinc galvanizing. So I’m trying to avoid a wire wheel or anything sharp that will scratch through it.





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[kavadarci]

I ah e the same dilemma, was this applied from the factory?

[Andy Somogyi]

Originally Posted by kavadarci

I ah e the same dilemma, was this applied from the factory?

Yup, factory Porsche rubberized undercoat applied in 1976.


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[tocobill]

Wurth makes a curved wire brush that strips this stuff away like butter ... DBS 3500. If I recall Eastwood also sells a version.

[SDFla7Nose]

Depending on how thick, old and brittle it is (or tacky)
Dry ice, Get 20 pounds, break it up and let it freeze the coating, then a scraper and a hammer should shatter it away from the metal. This can damage the underlying metal if you hit it too hard. This is more effective on sound insulation, but should work on anything thats rubberized that will get very hard when cold

Wire wheel works but makes a huge mess and can get clogged easily

an air powered needle scaler from harbor freight works really well, it will get clogged but ive had good results with one in the past, a combo of dry ice chilling and this would probably work best

Harbor freight needle scaler, its basically an air hammer with a bunch of thin rods that pulverize and chip off the material

https://www.harborfreight.com/air-needle-scaler-1108.html

[Oneredspyder]

Torch, spackling blade, wire brush, then coat with POR-15. Quick, easy, effective. You can top coat the POR-15. It is basically a question of what is you time worth, what is the car worth, what does it mean to you.

[SalParadise]

Multi-tool with flexible metal scraper head - ie. Dremel Multi-Max.

This tool is amazing. I did my entire floor on my '75S last summer in a couple of hours. The flexible head does not gouge the metal or mark it. It left all the factory paint under that thick tar and such completely intact. I love this thing. Never using a brush, wire or otherwise ever again.

[Edoyle]

With a quality wire wheel (cup brush and flat) you can remove undercoat without removing the galvanized coating! It takes some technique but very easy to get the hang of it. The wire wheels do polish up the galvanized coating and a quick pass with Scotch Brite before cleaning and etch priming is key for paint adhesion. I have done half my car this way.

[Dpmulvan]

Torch or heat gun with pnuematic scraper works well.

[Andy Somogyi]

Originally Posted by SalParadise

Multi-tool with flexible metal scraper head - ie. Dremel Multi-Max.

This tool is amazing. I did my entire floor on my '75S last summer in a couple of hours. The flexible head does not gouge the metal or mark it. It left all the factory paint under that thick tar and such completely intact. I love this thing. Never using a brush, wire or otherwise ever again.

It didn’t even mess up the factory paint and got the tar off!???

Wow, what’s the cutting head made out of?

I’m going to check out one of these, sounds perfect.


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[targa80]

I used a heat gun and scraper in 2002 to remove bulk of undercoating. Harbor freight sells the vibrating cutting tool for under $25 and if I had to do it today that is what I would use instead of the scrapper.

[KTL]

I too used the oscillating scraper tool thing. I bought a cheapo one from Menards since I figured it would be disposable. It worked really good on the interior floor asphalt sound deadener in my racecar. It's definitely worth a go on the exterior floorpan undercoating. Just keep in mind that the rubberized stuff is more resilient than the asphalt and the rubber also seems to adhere better to the metal. I found the tool works better when things are more on the hard side of things instead of soft. It'll cut through the soft stuff no problem but you can still have that residual layer on there that's a pain to get lifted from the surface.

[Andy Somogyi]

Originally Posted by KTL

I too used the oscillating scraper tool thing. I bought a cheapo one from Menards since I figured it would be disposable. It worked really good on the interior floor asphalt sound deadener in my racecar. It's definitely worth a go on the exterior floorpan undercoating. Just keep in mind that the rubberized stuff is more resilient than the asphalt and the rubber also seems to adhere better to the metal. I found the tool works better when things are more on the hard side of things instead of soft. It'll cut through the soft stuff no problem but you can still have that residual layer on there that's a pain to get lifted from the surface.

I’ve had decent luck with Menards tools, I bought a belt and orbital sanders to finish my porch. They were cheap, like $25 and I honestly didn’t expect them to last more than a few hours (that’s all I needed them for), but they’re still working.

Harbor Freight quality has Drastically improved, used to be complete trash 15 years ago, but today, I’d say HF is better than Sears.


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[SalParadise]

Originally Posted by Andy Somogyi

It didn’t even mess up the factory paint and got the tar off!???

Wow, what’s the cutting head made out of?

I’m going to check out one of these, sounds perfect.


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I am going to take a picture of my floor pans to show the mint factory paint coating it preserved underneath. It's so mint and unmarred that I am going to put a clear coat over it to preserve what a real untouched factory floor looks like. I'm serious.

Get one of these. It's for real. Just get the flexible head scraper. I bought three heads and only used one on the entire floor.

[Bob Kontak]

Originally Posted by SDFla7Nose

Harbor freight needle scaler, its basically an air hammer with a bunch of thin rods that pulverize and chip off the material

https://www.harborfreight.com/air-needle-scaler-1108.html

Yes, Sir!

[Bob Kontak]

Originally Posted by Andy Somogyi

It didn’t even mess up the factory paint and got the tar off!???

Wow, what’s the cutting head made out of?

I would say tempered steel. Harder than mild but by no means carbide. You will burn through a couple and I like this option better than the needler. These are great for plunge cutting in carpentry work but will tire quickly if they have to chew through a few nails.

The hefty Dremel machine will be spendy. A fein tool derivative. Worth it.

Needler is cheap. May be a good option for patches where the Dremel tip does not fit with ease.