Has anyone ever used expansion foam for autobody, filling holes?

 

The stuff from Lowes and Home Depot has been used with bad results. It sucks up moisture and causes more rot from inside out. The OE's use a structural foam, sometimes called pillar foam that is closed cell foam unless you cut it, then it is open cell foam and will suck up moisture and cause rot from inside out.

 

Really not recommended. It's made to fill voids not to patch hole in metal.

 

I'm pretty sure the expanding is closed cell. (I could be wrong there?) That said, there will be condensation on anything cold, (like metal), and it will then rot unless it has one heck of a bullet-proof paint job. If course it will have no air circulation.

My dad bought a camper van from the rust belt and brought it out here. He wire-wheeled a bunch of rust, then hit it with red rustolium out of the rattle can. (what they were selling in the early 80's). Where he put the foam, it actually helped with what was left of the metal, and sort or helped seal and hold things together, (at least from flopping around). Not pretty, not permanent, not "right", but for what it was, it worked.

Got a pic of the hole?

 

Stuff the holes with steel wool if you're going to patch them.

 

I've used that stuff a lot here at the house..... It hard to clean up and it doesn't like sunlight...... Idk I'd go with steel wool and bondo myself. Think of it like using newspaper in a hole the kids busted in the wall lol.
I bet you would have better results. On a side note it doesn't seem to draw moisture though.
You've got temporary fixes and lasting fixes..... I'm no auto body guy myself may work though.

 

It is closed cell until you cut, sand, or shave it. If you penetrate the skin it is an open cell sponge. Years ago the directions said to use a wet icecube to shape it to prevent creating a sticky mess. Probably the can has this info on the label

 

A pic of what he's dealing with sure would be nice. Almost anything I have tried, I didn't feel like the "initial adhesion", on the 1/2 funky worked. Yea, phosphorous, rob an oxygen and try to come back from H something...side story, I saw rust brake the edge of a concrete step as the re-bar expanded.
Seems rust can make allot of pressure.

 

Its just my rocker pannles are starting to rust out.