Painting the undercarriage to stop rust

[Thetireddad]

Hey everyone,
We recently got our bus from Kentucky and there is some decent rust underneath. My plan is to pressure wash then grind the rest down. Once it is clean I plan on painting underneath with a rust converter or any other options. My question is: are there spots underneath the bus where I should NOT paint? I’m not mechanical so please let me know even if it seems obvious. Also if you have used any products that helped I would love to hear about them. Thanks
Ryan

Has anyone used the hot oil treatments as a final coat? I’m from CT and it’s salt city up here

[Johnny Mullet]

Best thing to do is remove as much as the loose rust as possible and then repair any metal that needs addressed. After that you can use a rust converter like frame saver, POR-15, etc. If you are wanting to stop the rust from coming back, you need to oil the undercarriage every year. A popular product is called Fluid Film. You can also use motor oil thinned with mineral spirits in a pump sprayer and liberally coat anything metal under the bus and avoid the exhaust, rubber suspension bushing, rubber brake lines, and any electrical modules or computers.

I have a bus with some rust, but it's not severe yet. I drove it in the salt last winter and before this coming winter, I need to do exactly what I posted above to keep it under control. Cars and trucks that live in the rust belt and are oiled yearly before they began to rot out come into my shop and are in great shape because of it.

[o1marc]

I'm trying to picture how you would get the underside of a bus clean enough for paint to stick to?

[Mountain Gnome]

Paint is one thing. I say it's OK (if you can get it to stick like Marc said).
Oil/oil-based stuff, well, it's nasty, but helps your vehicle.

Rubberized undercoating (very much like spray-on bed-liner for pickups) is another story. Avoid that stuff like the plague.


My sister had an old 1980s Toyota Tercel 4WD with that stuff for the snow in the N.Carolina Mnts when she was in collage. I went to install struts, put a jack under the frame rail, noting how nice the underbelly of the car was despite the salted roads, and then the jack crunched the frame as I tried to lift this very light car. The rubberized undercoating gets micro-punctured from rocks, etc, then starts to peel away from the metal but stays in one piece. Then water gets trapped between, and rusts out the metal faster.

[EastCoastCB]

Originally Posted by o1marc

I'm trying to picture how you would get the underside of a bus clean enough for paint to stick to?

I've done it. Lots of time and effort.

[Marceps]

Was it worth it?

[pengyou]

Rent a compressor with a sandblaster? Use very fine sand.

[cweiss]

Exactly how much time and effort?

I'm trying to decide if it's worthwhile - I have a short-bus cutaway that has no metal sub-floor. The plywood above it is damaged enough that I'll probably replace it, so I'm assuming there'll be a stretch where the inside will be just a whole lot of open space.

I've got an angle grinder and flap disks/wire brush heads and that small HF media blasting cabinet which I could steal the gun from. I'm guessing it's messy AF - I've got a uptight HOA and can only push the RV storage unit owners so far

I wont really know how bad things are until I pull up the wood, it looks like it should get some kind of love from what I can see underneath...

[peteg59]

Unfortunately it looks rough.
If you don't have a place to do the tear down and renovation needed, put this one back on the market and find a better example with a metal floor and much less rust.
Anything can be fixed. You are the only one who can decide what is too much work, or not...
Good luck.

[Johnny Mullet]

Yearly undercarriage oiling like I posted above will stop that rust from getting much worse.