Let's say you were a little sloppy using that can of "Great stuff". If you didn't care about the surface it was on, how would you get it off - as in all the way off? Knife, that works just fine, but won't get it all off of concrete. Spackle knife, same as a pen knife. What will dissolve it - mineral spirits, lacquer thinner, diesel, acetone, ...
I'm just looking for a quick way to dissolve it so that I can do a proper job that the Great Stuff temporarily fixed.