Undercoating removal

Everyone has their favorite method. It's a messy job no matter how you cut it. I used a propane torch to soften and scrape with a putty knife - just sweep up the chunks. It really doesn't take a lot of heat. A gallon of Goof-Off or other solvent will remove the residue.

Factory undercoat is not as volatile to an open flame as some make it sound. Aircraft strippers are expensive and equally messy. I'd save that for paint removal. And, if you've gotten lucky with power washing the stuff off - more power to ya.