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Can anyone tell me if it is safe to use Rust-Oleum on moving undercarriage parts (like the driveshaft for example)?

Also regarding the undercarriage, should I spray it on or roll it on? And should I first apply Rust-Oleum primer and then Rust-Oleum paint, or should I skip the primer and just use the paint?

I'm in the process of painting an old school bus I'm turning into a camper. The upper body is pretty decent for being 20 some years old, but the undercarriage has quite a bit of rust.



For the undercarriage of a car or bus... you should be able to directly spray bomb the Rustoleum or Tremclad on. It would be easier than attempting to get into every nook and cranny with a roller and brush.

As for the driveshaft... you should have no problem slapping a coat of paint ( by brush or spray bomb ). The weight of the paint is so insignificant that it should not cause vibrations in the driveshaft.

One thing I would most certainly do prior to spraying the underside of a vehicle ( whether bus or car ) is to use a high pressure washer to blast all the road crap, dead animals, flakes of surface rust and other undercarriage debris off. This would give the paint a better chance at getting a strong adhesion directly to the undersurface.

Since Rustoleum/Tremclad are designed to be 'anti-rust' paints... they will do a good jobs at sealing up the undercarriage surfaces.

The main reason for thoroughly cleaning off the undercarriage prior to painting is also to ensure that the paint won't peel away or somehow separate from the painted surface. The integrity of the Tremclad/Rustoleum as an anti-rust solution under the vehicle might be compromised if water is able to find a way to get between the paint layer and the surface that has been painted.

The weak point to the plan is that once you have fully painted the undercarriage of the vehicle, I would assume that you in the future would have to be doubly cautious when putting a torch under the vehicle. I don't know for sure... as I have no real life incidences that I can fall back to explain this... but imagine the vehicle is in the shop and they are using a torch to cut off the muffler system or bolts off to do a replacement... I am not sure if a Rustoleum painted undercarriage might be more susceptible to catchings on fire ?

I would assume the risk is higher in the first year or so after the undercarriage is painted. After that I would assume that most of the flamable components of the applied paint will have been rendered neutral and not pose any greater risk then say motor oil or transmission fluid that tends to leak and gravitate to the undercarriage of the vehicle.

One potential benefit of the Tremclad/Rustoleum undercarriage painting is that it may work as a sound deadener and give better sound proofing then say an oil undercoating on the undercarriage.
The paint has a thicker skin when dried then a lot of the undercoatings sprayed on the bottom of vehicles.

The other benefit is that a year after 'the initial' Tremclad/Rustoleum undercarriage painting, you could probably take your garden hose, spray the undercarriage to loosen any road dirt and give it a supplemental spray bombing with the Tremclad or Rustoleum to simply touch up or boost the protection that you already have.. or to touch up any spots where road rocks have flown up and scarred the paint and exposed the metal surface below.


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