Removing decades old rustproofing

[frankc]

While I'm under the car this winter working on my suspension, I figured I would finish the job I started about 20 years ago and remove the remaining rustproofing from the bottom of my car. It is already gone from the wheel wells, which wasn't too bad since it was mostly a vertical surface to work on, but now I have to do the belly of the beast.

In the past, I sprayed on kerosene and let is soak (outdoors) overnight, and then went at it with toothbrushes and guitar picks. But now the stuff is even harder than before (30 years old). Is there a better way to do this? I do not want to use any flammable solvent this time around, so I'll use something citrus based. Can I use a heat gun to soften it up and then scrape off the majority with something non-metallic? And then follow that up with the solvent & brush (to get into the crevices from the chip guard).

thanks for any advice,
Frank

[competentone]

I've never tried it on undercoating, but dry ice can be effective in making some adhesives brittle allowing them to be "chipped" off the surfaces they are adhered to. It might be worth a try.

[vanwyk4257]

This may not be the most pleasant way to do it, but I stripped most of the undercoating from a '72 911 using an angle grinder and a knotted wire wheel. It goes through the undercoating like a hot knife through butter and leaves the metal underneath nice and clean so it's ready for priming and paint.

[frankc]

Dry ice - Hmmm, I never thought about going that direction with the temperature. Something to try.

I should have mentioned that my goal here is to leave the underlying paint intact. I guess the only good thing about having this stuff on there is that the paint under it is still in very good condition, just a little discolored.

I should also have mentioned that this is not the cosmoline put on by the factory, but rather the tar stuff put on by the PO when new. Given that I can count on one hand the number of times I've driven the car in the rain in the past 20 years, I don't think I really need it.

[frankc]

I know it has been a while since I started this thread, but I thought I would post an update on the process I found that seems to work fairly well in removing the tar based rustproofing product applied over paint. For those of you not familiar with this process, it was something that was done years ago (not sure if this is still being done) to cars up north to protect them from the harsh winters. My car was originally purchased in Pittsburgh and was "rustproofed" when new, although I purchased and "rescued" it 8 years later.

Now for the process (and some pics).

1. I start with a heat gun on low and heat an area about 6 square inches, stopping when I can see the material begin to almost melt. I then use the flat edge of a guitar pick (something not abrasive to avoid damaging the paint underneath) to lightly scrap the stuff off. In most cases it is VERY soft at this point and comes off like soft butter. I can use the corner so the pick to get into the inevitable nooks and crannies formed by the chip guard under the paint.

2. I then use 3M General Purpose Adhesive Cleaner and a toothbrush to remove the thin film of rustproofing remaining. Brush a small area, then wipe with a disposable shop towel. Be careful here. If you brush too hard or long in one area, the paint is thin under the car you will start to rub it away on the high ridges.

3. Spray the area with citrus cleaner and let sit for a few minutes. Go back with a (different) toothbrush and clean up any remaining little areas. Then use a long soft bristle brush with water to wash the whole area. Do this a couple of times to remove as much cleaner as possible. Dry the area.

4. Now wax the area with cleaner wax (never on the top side though ). This will remove any lingering residue of the rustproofing and clean things up nicely. Buff it off and enjoy.

In the pictures of the center section, you can see the difference between the clean driver's side, and the passenger side which I will work on next.

Note that the paint on my car is a silver metallic, so the bottom-side paint is a light gray color - does anyone know what color this is? I need to touch up some areas.

Area after heating and scraping off the rustproofing (Step 1). I believe the amber material under the black rustproofing is the original cosmoline:


Same area post waxing:


Floor pan shot - notice difference between driver's side (closest to camera) and passenger's side:


Another floor pan shot. Some of the dark spots are normal chips and scrapes one would expect to find under a car, and some are spots which still need to be cleaned-up:

[Jagshund]

Looks good. I used a 3" putty knife and the occasional blast from a propane torch. Only issues were in the corner of the wheel wells where the knife made reduced contact with the surface.