stop frame rust, insulating, & wood rot prevention

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stop frame rust, insulating, & wood rot prevention

Postby Bob Hammond » Tue Aug 28, 2018 6:23 am


I'm replacing sections of the rotted subfloor of an Airstream (a problem common to almost all RVs), and I thought I'd share a few things that I learned from this job and also from building my woodframed foamie, the Nutmeg.

After removing the rotted plywood in the Airstream, I found sopping wet fiberglass batts in the underbelly, complete with snails and wasp nests. After excavating this nastiness, I found that the frame was not seriously rusted. After knocking off the loose rust and scale with a wire brush, I painted it with a paint that transforms the rust permanently to a polymer. There are several brands - "Paint Over Rust", "Chassis Saver", and they cost about $50-75/quart, and there are other treatments that also convert rust. Note that these products work best with rust, not bare steel. For those who build their chassis from scratch this might be a good option.

After painting the frame, then I cut EPS to fit between the frame beams and glued them in with Gorilla glue. It's probably a good idea to punch a few drain holes to allow any seepage to escape. The beams of an Airstream are 5-1/2" deep, so there would be a 3-4" airspace between the EPS and the aluminum bellypan (hmm, do any tiny trailer builder install bellypans, and would that have any advantages?

Recently, I have discovered a treatment used for log homes to prevent/treat insect damage and fungal rotting. One product is called Timbor, and here is a link to a discussion on an Airstream forum. It can be applied before or after installing the wood, so long as it hasn't been painted. ... 84474.html
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Re: stop frame rust, insulating, & wood rot prevention

Postby Andrew Herrick » Sun Oct 28, 2018 9:22 am

Thanks for sharing all your valuable information! I would add to that that one of the main reasons for a rotted floor or roof deck is the accumulation of condensation from warm, humid air indoors on cold exterior sheathing. If you don't have a completely sealed wall, floor, or roof assembly, it should be designed to dry to at least one direction. And a vapor retarder on the humid side is always a good idea :-)
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