Hey gang, been trying to get the 40 year old undercoat clean in the wheel wells. It's getting there, but it's taking lots and lots of scrubbing. Even using a small steamer on it! Can I apply a very light coating of say 3M rubberized undercoat over the existing to make it look more presentable? Or, will there be adhession issues? Definetely don't want to scrape the old stuff off. Thanks.

Yes you can but....If it's peeling it will continue to peel.
Lacquer thinner, lots of rags and good ventilation will get it off.

When you do undercoat toss a little bit of urethane hardener into the mix.

This is what I used on mine. Works great just have to be careful about letting it dig in too deep. Once you get under it, comes right up.

Air Chisel

It's always best to get the old stuff off, undercoating can seal moisture in, depending on what you are using. A very popular product in Eastern Canada where the use of road salt is obscene but necessary is Rust Check, messy but very effective and it creeps into cracks etc. which is very desirable, I get all my vehicles done every fall and the difference between mine and an untreated vehicle is quite astonishing. Getting all the old stuff off allows to see for real what condition your car is in, no guessing, address any areas that need addressing and then apply new product, whichever you choose, at least you now know everything. My .02 worth.

Ian Stott
Moncton
Canada

take off what is loose and pealing and spray over the rest...works fine and sticks fine. I used rattle can undercoating.
10 years and still looks great....in NE with salt.

Rich

Thanks guys, figure that would be a heck of alot easier than scrubbing the old stuff clean. I'll wait till a nice hot summer day to make sure all the moisture is out and it bonds well then.

Now will the 3M product get tacky on a hot day and collect dust? I know the ziebart stuff does, and want to avoid anything that.

I'm using Naphtha to remove old tar and undercoating. It eats through tar and undercoating.

Tod,

Use the wonder product of the ages - WD40! Cleans the old indercoating, while inducing it to resume some of its level of flexibility. Spray in onto throwaway towels liberally & rub down. Let set for 24 hours & do it again. You'll swear that the undercoating is new. Yes, it will be slightly tacky, but only for a couple of days, because wD40 dries. After that you CAN use the 3M product if you wish, to fill voids. But, I would suggect NOT using the rattle can version because the texture will be obviously different. Get the specified gun, bulk version, and use no more than 30 psi to spray it. Blends well. Looks great. Works like a charm.
BTDT. Just can't find the gun, though I think I lent it to a fellow Porsche guy in Redlands. Otherwise, I'd send it to you. But it's cheap.
Pat

The directions on the stuff I use says you can apply undercoating over undercoating as long as it is first undercoated. I'm a little confused. Did you know they make really great wine here in Paso Robles?

lol too funny. Is that like preboarding Elliot? Getting on the plane before you get on the plane?