Body/Trim: Underseal re coat

[howarddj]

If i want to re do the underseal on my car, do i need to strip all the old stuff off before i re coat, or can i just treat any rust patches and leave the rest, just recoat over the old?

most of the underside of the car is perfect, but there are a few small patches of very light dusty surface rust, the kind you can rub away with your hand. also alot of the underseal has come off from the inner wheel arches where i went a bit mad with the jetwash, exposing all the badly painted metal.

i just want to get rid of anything loose, kurust the rust patches and re coat the entire car top to bottom, but i am worried it will not stick to the old coating.

thanks!

[Steve and his 244]

Get it up on some axle stands to access the underneath and jetwash the hell out of everything, to do exactly like you did on the wheel arches - remove any loose stuff. If its loose, then its likely that water has got behind the dried up underseal and may be holding rust.

After this you need a few warm days with the car outside to make sure that all the water dries out.

Then when it comes to actually doing the job, obviously make the job easier for yourself and get the car as high up as you can, wear old clothes and overalls and goggles and an old hat (underseal in your hair is NOT pleasant) and wire brush any remaining suspect patches of underseal.

Deal with the rust. sanding the rust does not remove it, it just removes it orange surface growth and leaves the pitting in the metal. Use a grinder and dont be afraid to "skim" the metal down in places to remove the pitting. Red oxide or zinc primer, then paint.

Now underseal it. Just go over the top of the sound original stuff, and put two coats on anywhere where you have carried out repairs.

I would also consider injecting the box sections with wax rustproofing such as dinitrol.

Steve

[howarddj]

brilliant thanks steve!

[Angie]

I'm having some bodywork, mainly wheel arches, done, and the repairer, who does a fair amount of classic car work, is planning to pressure wash and waxoyl the underside of the car. Is that a bad idea? Should I suggest renewing underseal instead?

Sorry to hijack!