If it's real thick, just make sure you soak it down well and let it sit. You may get a layer off at first, then do it again. I had one side that was that way. I did both of my rear fender wells in little over two hours, (after letting it soak over night) that includes a final cleaning with my pressure washer. BTW, I did my front fender wells the old way, I worked on them on and off for a week and still wound up finishing them with the Goo Gone.
