Underbody Paint/Undercoat

[ehrawn]

Can anyone recommend a product for light touch ups under the floorboards? I'm slowly making progress getting 30 years of crud off of the undercarriage. All of the metal appears good to go, but I want to apply something to prevent any rust on the newly exposed bodywork.

[82eye]

Can anyone recommend a product for light touch ups under the floorboards? I'm slowly making progress getting 30 years of crud off of the undercarriage. All of the metal appears good to go, but I want to apply something to prevent any rust on the newly exposed bodywork.

por 15 is a good product many use. follow up with undercoat.

the underside of the car is not a good indicator. a better measure is pulling the interior carpet and checking the floorboards from the inside. the cars rot from inside to outside. by the time you notice it on the bottom the rust is either extensive or fatal.

[ehrawn]

I’ve had mixed results with POR-15. Better luck with interior than exterior because prep is harder.

good tip about pulling up the carpet. I didn’t even think about that.

[Panici]

I wouldn't use POR15 personally on sheetmetal/bodywork.

I've used it on bare "de-rusted" metal like subframes and differentials that still has rust contamination.
It needs rusty metal to bite and chemically bond.
The prep is multiple steps and if you don't get it right I've heard the coating will fail.

I have used both Rustoleum Oil-Based paint (brushed on) and rubberized undercoat in the past. Found that paint chips off with rocks and that is why rubberized coating is better inside wheel wells, and probably under the car as well.

I'd start with either a rust converter or etching primer depending on the state of your base metal. Follow up with paint, and then rubberized undercoating. Make sure you allow plenty of cure time between products lest they react with each other.

[tomstin]

I have had good luck with POR15 but the prep is CRITICAL. Do NOT shortcut the prep steps! Also, I use the 6 pack of small cans. When you are done, a shot of welding gas displaces the O2 before closing the lid and the product will store much longer.

I do agree it is finicky to use!

[packratbimmer]

Use an etching epoxy primer and go from there

[moatilliatta]

I don't understand people's love affair with POR15 and rubberized undercoating...

Etching Primer, Sealer, and some 3m Seam seal to replicate factory rock guard for patched areas on the underside if needs.