Q: I need to fill some gaps I have in a welded aluminum frame. What is the best “Bondo type” filler that won’t outgas too badly and ruin my finished powder coat?
I would prefer an epoxy or something that wouldn’t necessarily need a preheat or super-long cure time, but I do understand there are tradeoffs and I probably won’t be able to find a product that applies to metal, dries and sands smooth, and doesn’t outgas. Any recommendations would be great.
A: Your observation regarding fillers is right on the money. Traditional auto body fillers based on polyester resin (e.g., Bondo®) work fine for room-temperature-cure applications such as refinish paint, but they blister and outgas at the elevated temperatures typical for powder coating cure.
There is a solution, however. Alvin Products has a material called Lab-metal that works well as a high-temperature filler for parts to be powder coated. It’s a one-part, aluminum-filled product that is easy to apply.
Please note that the company specifies that Lab-metal is good to 350°F, so the powder coating you use will have to cure at a temperature below that. Since low-temperature-cure powders are fairly common, your coating supplier should be able to suggest a powder that’s right for your application.