Fender Warpage

[WillBilly53]

okay a couple things here.

first the hood. this seems heavier and thicker than the rest of the sheet metal (fenders) on the car. can i sandblast the hood or will it warp?

also i was speaking with someone today and stating how i'm stripping the fenders with a drill and various 3M rust/paint stripper wheels.

he said that i could probably use ground corn cob in my sandblaster on the sheet metal without it warping.

is this true?

okay another question. when i weld say a small patch (say 18" by 18") on a fender am i taking a chance on warping it?

thanks!

[NTX5467]

If you haven't done any sand blasting, with full-scale equipment, I can say from first hand experience that it IS a "dirty and dusty job". I think I'd use some chemical strippers that will not abrade the basic metal underneath. Sand blasting with that equipment is much different than using a blast cabinet, for suere.

When we first did our "deal" a good many years ago, sandblasting was the only way to do things as the chemical strippers were not that available just yet and the plastic media and such just had not been developed yet. So we went to the equipment rental place and rented the whole deal (pressure pot, that allegedly had no moisture in it, the air compressor to run it, and the space suit to wear while doing it). Boy, did we look like we knew what we were doing!

It is ABSOLUTELY necessary that no moisture be anywhere inside the pressure pot or you will not get a smooth flow of sand out of the nozzle! Just daytime temperature swings can put enough moisture in the pot to cause problems.

Then there's the multiple bags of sand of varying grit ratings that you'll need. Coarse for the first clean up and progressing to Fine for the final dressing of the metal. Not to mention the technique of holding the nozzle at the correct angle to and distance from the panel being cleaned.

As for warping, remember that you'll have sand exiting the spray nozzle at a good rate of speed. When that sand hits the surface, it will put some localized heat into the surface as the sand hits the surface and bounces off, taking some of the paint with it. This heating and cooling can cause some warpage of the base metal if you try to go at it too quickly and do too much too quick. PLUS, if you concentrate too long on one particular spot, the sand will actually make a low spot there--another reason to always keep the nozzle moving.

Similary, using a DA sander or one of the stripping wheels can probably do more harm than sandblasting. Both will put heat into the metal as they take the paint off and that's where the warping comes in. Both create dust and debris that will have to be cleaned up too.

I personally feel that a quality chemical stripper (like Eastwood Company sells, for example) is the best way to strip paint from sheet metal. If there's any heat built during it's dissolving the paint, it'll be on the whole panel instead of just a very localized portion, I suspect. It's much more environmentally acceptable too, without all of the particulate hanging in the air. Easier to use too--just wipe it on and then squeegee it off in a few minutes. In many cases, if you time it correctly, you can stop at the factory original primer or you can continue to the bare metal. Key thing is that it will not abrade or degrade the basic metal panel surface.

One of my friends was going to strip his car using a DA sander and lots of adhesive discs (as they come on a roll). When done, he said "Never AGAIN".

Be sure to investigate ALL alternatives before doing something of this sort. I've "been there" with sand blasting and others might have other orientations. If you're confirmed on sand blasting the car/panels, then let a professional do it instead of doing it yourself. Of course, if you have another vehilce to practice on, then you might get good at it before you do your Buick.

Most of the sheet metal will probalby all be of the same thickness or gauge. What will make some more brittle than others is "work hardening" as the metal ages plus the way it's shaped/contoured.

I wish you luck in your project.

Enjoy!

NTX5467

[Guest Skyking]

I agree with NTX. I stripped my Metropolitan last winter with paint remover. The car had the factory paint & primer, plus a second coat of paint that someone along the line painted. It is far less messy than sand blasting. I could never have blasted that car in my garage. I used a product called Zar, purchased at a local hardware. It worked great but the fumes were bad. After I stipped the complete car, I washed it down with steelwool & laquer thinner to remover every trace of paint. If I had to do it again, I would use a much safer stripper.

[WillBilly53]

thanks for the reply and info NTX (and skyking)!

i did some chemical stripping today on one of the fenders. boy did that go fast. i started out doing it with the 3M stripping wheel it took me about 15 minutes of conitinuous manual stripping to get about a 16" area down to bare metal. Laid down a huge tarp outside, i then got a few cans of aircraft remover, put on the my respirator and goggles spray the whole fender. waited about 10-15 minutes for the spray to blister the paint. took my plastic scrapper and it came off like a charm.