Boy,, that's a tough one. I've never flown off cement or asphalt before. Which is this? I get oil out of my cement drive by spraying it with Espree Wheel Magic,, scrub it lightly then let it sit for an hour or so,, spray and scrub again,, then hose and scrub it off. Why don't you get a 4x8 sheet of 1/4 inch plywood and take off and land on that,, or a piece of old carpet.

Mike