Undercoating residue

[DanMcG]

I'm in the process of removing the undercoating off of the wheel wells on my 85 Chevy truck. It's coming off fine with a heat gun and wiping it down with mineral spirits, but there is still some residue left. It appears to be an asphalt based coating. Which cleaner would work best for removing this.
Thanks!

 

[chevman]

Try not to overheat it and you will have less residue.

 

[DanMcG]

Well it is what it is and I still need to prep it properly.
Thanks.

 

[elwood]

Try acetone.