Did My Improper Great Stuff Foam Use Cause Frame Rust?
A 22 year old economy car in New England is going to have a lot of rust on it, unless it lived in a garage and was driven by a little old lady who avoided snow (and road salt). So five or six years ago, when a friend of mine mentioned that four wheel drive off-roaders filled their frames with Great Stuff foam to combat rust and corrosion, I figured I'd give it a shot. After all, there were plenty of little holes rusted in my unibody subframe already that I could stick the applicator straw through and fill.
Well, filling up with foam seemed like a smart idea at the time, but when I took the car off the road this week to start a rehab project for the ifitjams website, I realized that in most places the Great Stuff was doing great and the steel was doing poorly. In fact, the steel was so corroded that the if it wasn't anchored in the Great Stuff, I think a lot of it would have fallen off the car a long time ago. Maybe filling the frame with foam makes sense when it's pristine from the factory, but here's what I found digging all the Great Stuff out (and it did hold up great!)
I'll admit I never read the can, they might have warned dummies like me about foaming a unibody that had already started rotting away. What I found pulling the foam out was that it was often damp, despite the fact that the car had been sitting in a garage for the last month. Whatever water got in or moisture that condensed on the steel out of the air appears to have persisted because the foam (closed cell, I believe) kept the air away from it. Keep steel damp, mix in some oxygen, and you get rust, rust, rust.
None of this is intended as a knock on Great Stuff, it does a terrific job for insulating houses and filling all sorts of spaces, but I'd think twice about shooting your car frame full of it. After the fact, it occurred to me that those off roaders may have filled up with foam for flotation reasons when they hit the water, not to prevent corrosion. Those trucks have real frames, and the drivers usually beat the mechanicals to death long before any frame rust can have a serious impact.
Well, filling up with foam seemed like a smart idea at the time, but when I took the car off the road this week to start a rehab project for the ifitjams website, I realized that in most places the Great Stuff was doing great and the steel was doing poorly. In fact, the steel was so corroded that the if it wasn't anchored in the Great Stuff, I think a lot of it would have fallen off the car a long time ago. Maybe filling the frame with foam makes sense when it's pristine from the factory, but here's what I found digging all the Great Stuff out (and it did hold up great!)
I'll admit I never read the can, they might have warned dummies like me about foaming a unibody that had already started rotting away. What I found pulling the foam out was that it was often damp, despite the fact that the car had been sitting in a garage for the last month. Whatever water got in or moisture that condensed on the steel out of the air appears to have persisted because the foam (closed cell, I believe) kept the air away from it. Keep steel damp, mix in some oxygen, and you get rust, rust, rust.
None of this is intended as a knock on Great Stuff, it does a terrific job for insulating houses and filling all sorts of spaces, but I'd think twice about shooting your car frame full of it. After the fact, it occurred to me that those off roaders may have filled up with foam for flotation reasons when they hit the water, not to prevent corrosion. Those trucks have real frames, and the drivers usually beat the mechanicals to death long before any frame rust can have a serious impact.
posted by Morris Rosenthal at
4:32 PM
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