Opinions on undercoating (2024)

While it's not a B-body, I think the problem applies to all cars. The Dart I picked up a few weeks ago is an extremely solid, rust free California car. It was not undercoated from the factory, and this would probably be a death sentence if it hadn't been garaged and only seen 47k miles in its life. As I get ready to swap drive trains, I'm wondering what to do with the underside of the car.

The undercarriage is oily and messy, but the metal is in near perfect condition. There is likely some surface rust hanging about, but nothing serious. As this car is going to be a daily driver, I was planning to undercoat it- both for noise control and metal protection. I'm not concerned with factory correctness here. In the past, I've used Eastwood undercoating to fill in and repair problems. I have an undercoating gun and it was very easy to do. The stuff has worked well. However, I'm worried that when I go clean this car and prep it for undercoating, I'm going to lose what's left of the paint or primer that was still there.

Eastwood has a "rubberized rust encapsulator" that I've used before too, but I can't yet comment on how it holds up. I've also used products like Rust Bullet and Blackshell with really good results. I am, however, skeptical of all rust solutions short of cutting and replacing metal. Since this has at most some surface rust down there, I think any of these products would be a step up from leaving it more or less bare to road debris and moisture.

Should I:

1. Leave it alone!
2. Clean it up, undercoat and be done?
3. Clean it up, shoot some rust encapsulator-type undercoating, and go?
4. Clean it up, paint it with a product like Rust Bullet, then undercoat it?
5. Clean it, rust encapsulate it, then undercoat it?

Any thoughts and experiences welcome!

Im going to go with option 2

I also love the fact that you are going to daily drive it

Take a look at Lizzardskin http://www.lizardskin.com/

Thanks for the opinions. Bed liner and lizard skin were two other options. I've previously decided not to do lizard skin based on the price, but reviews are good. Since it is a newer product, I wonder about how well it will stand up on the outside of a car. Having done peel-n-stick sound deadener inside 3 cars now, I can say it's a pain. And it's not cheap either. It can cause fitment issues with seats too.

I'll keep thinking. Any more first hand opinions on lizard skin/bed liner as an undercoating would be appreciated.

I do not like undercoating.

Many times I have seen a car with undercoating and it looks fine, then you see a pin hole in it and scratch at it and a just falls off with rust.

Problem is you get a chip in it then moisture gets under the paint, if it gets under the paint it spreads along under the paint and the undercoating does nothing to stop it, and hides it so you don't see it until late flakes of paint and rust are coming off.

I'd probably just mist some oil into the frame rails, and put clear on strategic areas underneath like seams, brake and fuel lines. I also rattle can my exhausts when new with high temp engine clear, smells for about a week, turns a golden brown around the cats but keeps the rest of the exhaust looking new for years, only rest spots are from stone chips in the clear.

I'll even knock off loose rust and clear over whats left . It may not look pretty but I have the mental peace of mind when I look under my car I know EXACTLY what I'm dealing with and don't worry about rust hiding under spray paint or undercoating I can't see.

Resto Rick has all sorts of options. Check it out.
I'm in California. The cars I see out here are about 50/50 as far as having full undercoating. I never add it if the car didn't come with it. My Charger was a St Louis build, registered in Ca since new.

According to the restoration gurus, the under side was never fully painted. I say....So What? I like mine painted

Cranky said:

I'm with The not so tall man. After removing undercoating from a lot of cars over the years only to find trapped moisture and rust in the seams etc, I really hate the crap. It adds weight to the car and sucks at sound proofing. In fact, I'd rather spray the underside with 90 weight oil than undercoat it. Kern Dog, that's the way I like the bottom of my cars to look.

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All the more reason to use bedliner, you cannot chip it no matter what you do............ it's rubber and it's on there! Living where I do painting the bottom of a car is not even an option and I hate getting covered in oil every time I crawl under my car.

Somewhat off the beaten path here, but what about body plugs? I can't quite figure out why they are in the floor pan, other than for letting prime out of bodies that were dipped at the factory. Once the floor pad and carpet is in there, good luck getting the plug out to remove water from a dunking. At least that is my perception.

If I welded those shut before applying bedliner top and bottom, would it hurt anything at all?

318 Six Pack said:

Somewhat off the beaten path here, but what about body plugs? I can't quite figure out why they are in the floor pan, other than for letting prime out of bodies that were dipped at the factory. Once the floor pad and carpet is in there, good luck getting the plug out to remove water from a dunking. At least that is my perception.

If I welded those shut before applying bedliner top and bottom, would it hurt anything at all?

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I see no problem welding them shut, not sure what they're for because like you said it isn't like you can pull the plug?