Repairing/Restoring Undercoating

[bburcha]

Hello all, Some of the undercoating is flaking off the bottom of my 68 911S and I want to repair to original. How and what material do you recommend to treat the exposed bare metal?
Also some bare metal in trunk. Do I paint with semi-gloss black?
Thanks in advance for your suggestions.
Enjoy your rides,
Bruce

[kenikh]

Some might disagree, but I like to use a phosphoric acid wash on exposed metal, like POR-15 rust treatment or concrete etcher (same thing). It leaves a nice, rust proof phosphate coating on the steel, which can be painted over nicely using new undercoating. Just make sure you rinse it all off very well, as it will continue to etch the metal if it remains.

(edit) BTW, the 68S didn't come from the factory with undercoat. Sounds like a previous owner must have done it.

[rngpc]

I have a 69 with undercoating flaking off here and there with bare metal underneath too. There are no rust holes, just surface rust. The undercoating just falls off. It seems useless to try to patch because so much has come off and it seems there is slight surface rust covering most of the floor pan.

I think is would be best to get rid of it and paint and re-undercoat. Has anyone out there tackled this job? What is the best way to do it, just use a wire brush to remove and then sand, paint and undercoat?

[kenikh]

If I remember correctly, Wurth made a special tool just for removing this undercoating. I seem to recall one member of this board owning one, but they are pretty much unobtainium. Even with the tool, removing that coating is hard, hard work. Hopefully he can add his 2 cents when he reads this.

[Sacto S]

I recently removed about 90% of the undercoating on my '67. I found that heat was not effective. Heat only made the old undercoating gummy and left behind a lot of scum still covering the surface that required additional attention. For me, the best method was to use a stiff bladed 1 1/2" putty knife. Scrape off no more than 1/2 inch at a time and it goes pretty quickly. If you attempt to take a full blade width, the putty knife just skids over and requires a lot of muscle. Small is better in this case. Stop every 15 minutes or so and take a file to the blade to keep it very sharp. When I was finsihed, I had the car media blasted and a coat of epoxy primer shot over the whole thing. I'm not sure if I'll apply new undercoating during the repaint process or not. I kind of like the clean racey look of the exposed painted body panels.

[SERIES900]

the early undercoating,up to , guessing 69 as i recall, is hard and flaky as oppose to late model rubbery. early u/c removes well with scraping cold, or blasting, rubbery late u/c needs heat and scrape or the wurth tool, sold by snapon also, blasting just bounces off that stuff!!

[RPMClassic]

Just chimming in, as I have suffered through the complete removal of undercoating both inside/outside on 2 projects. The wurth tool was definately a valuable tool - although after spending all the money on it, it now just hangs on the garage wall!! Damon is the pro when it comes to this stuff, however for those of us who chip away on these projects at home with limited time, limited money and limited tools - this tool was a good buy compared to the overall cost of restoring the car. If anyone is undertaking such a project - my tool is available for rent or purchase - as I will NEVER subject myself to such a project again. I recall it was close to $600 bucks or so a few years ago , prices have surely come down since then. $250 buys it if anyone is interested.

Good luck with the projects.

[Tom F.]

I'd love to see a picture of this tool.

[kenikh]

Isn't this it:

[A.T.]

I'm almost a little embarrassed to admit just how acquainted I am with that tool. I may never forgive the owner of my preferred body shop for having introduced me to it. (He likes to encourage do it yourselfers.)