Imperial Homepage -> Repair -> Paint -> Undercoating
Question from Marc:
I wanted to spray undercoating on my Imperial, but I was wondering if ALL the light rust has to come off, or if I can spray it over top. Its just surface rust. very light in places like the trunk and such.
YES - the rust MUST come off or be neutralized - at least "kill" the light rust with Oxi-Solv, Ospho, a generic acid prep, or something like Corrorless. The typical "rubberized" undercoating has no rust-fighting ability and the rust will continue, well hidden.
After growing up in Florida I'd say remove the rust no matter how light. If you spray over it all you will be doing is trapping the moisture and making your problem worse.
Question from Dave:
What is the consensus of opinion of underbody coating on restored cars. Is it better to have underbody coating as it came out of the factory or a painted finish equal to the outer body panels.
Reply from Kenyon:
I would use the rough, rubberized modern underbody coating for sound deadening and sealing properties. Doubtless someone on the list will be more product specific. How close to original depends on budget/performance properties of the various options and concern about the non-visible area of your beautiful car meeting rain or judges' eyes and surviving.
I would not just spray a glossy coat of body grade finish, as I interpret your question to ask about.
My buddy that does non-imperial "show" cars that he puts mirrors under at shows skips painting them and goes directly to diamond plate and chrome. Everywhere.
I doubt that's the thing that you may have had in mind.
Question from Eric:
So I'm laying on my back under the '56 with my one inch scrapper, getting "stuff" in my eyes, and I say, "there must be a more civilized way to get this ...... off. Who is the expert out there?
I got similar thick "pudding" off the underneath of my old Humber with industrial paint stripper. What you do is to score into the undercoating with a sharp blade, bush on the paint stripper and ( you'll like this bit ) go down the pub for an hour. When you get back what hasn't fallen off comes off with hardly any effort.
I have found that the best way to remove undercoat is with a small torch. I use the kind with the disposable bottles that you buy at the hardware store. Any kind of high heat is the best. It will also will work with a heat shrink gun. Just remember that gas lines are not the place to be around with a torch.
I think you have mastered the technique as well as the rest of us. Ain't no easy way. Be sure and wear goggles. The only thing that makes it easier is having it on a lift. SOMETIMES, pressure washers can take it off but they can also get water in the interior if you have holes in the floorpan.
Question from Stan:
Has any one ever heard of a type that does not dry that stays a little wet to the touch. The reason I am asking the question is a I am looking at a car that look to have 11k original miles the only thing that looks a little out of whack to me is the undercoating. The wet to touchiness of it.
When I worked for Quaker State Oil we had a brand of undercoat that we sold to dealers in canister form that had a small gun that attached to the air hose to fill tires. It was a solvent type and did not dry to the touch. It always stayed a bit sticky. I do not know if this is around any more as Quaker State quit marketing it many years ago. The new car dealers used it all the time. We also carried it in a 35 gallon drum with a pump that replaced the lid on the drum. I used to have to rebuild the pumps and the only way to brake this product down was to soak it in solvent.
Sounds to me like someone recently undercoated it., an old used-car dealer trick to hide underbody rust. I'm not sure how old this 11K-mile car is, but undercoating should be completely dry within days. Sometimes home-applied aerosol types stay tacky a little while longer, but if it comes off on your finger on a cool car, something seems amiss.
If it's purported to be factory undercoating, and the car has 11,000 miles on it, every piece of road grit the car ever drove over should be stuck in the underbody goo you seem to be finding. It would look like a cake frosted with toasted coconut (only upside down).
If it gets soaked in gasoline or oil, it could possibly dissolve or feel soft in some circumstances, but not a common thing. Smell it to see if it has something besides water in/on it.
Use common sense when doing so and don't hurt yourself in the process.
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