Try biodegradable degreaser instead of antifreeze, I use something comparable to simple green industrial cleaner (Jungle Jake works best if you have it in your area). You can find something similar at a local hardware or automotive center in the automotive chemicals/car wash section. Ive had good results with light-medium varnish and carbon build up. Heavier im not sure, but it doesn't hurt to try it. Can always go to antifreeze afterwords. Plus the simple green does wonders on other stains on concrete to jeans!