No... Cleaned all the mold off easily with the spinner and rotary. I use a high alkaline concrete cleaner for 98 percent of all the cleaning. Everything came up, gum, mold, rust, except the black stains from the leaves.
We did not try bleaching it out yet. That might be all it takes. We tried a peroxide based cleaner and it lightened a bit.I'll need pic to make sure. F9 should work on tannin stains. Most tannin stains are orange. Black could be mold or a sap residue. If its a sap residue, a strong sodium hydroxide used in combination with a stiff bristled broom and the power wash at 200 degrees will help. But sometimes they can be so deeply embedded that even acid washing won't do it.
Rob, post a pic so I can see how bad they are. The orange battery burn can travel 2" deep into concrete. We recommend to surface clean the concrete first, let it dry completely then a double application of F9 allowing both coats to dry and follow the outline explained in our battery acid removal videos. This will make it look about 95-100% on average.Hey I left my golf cart on my new driveway and it left orange rust looking stains after a big rain. I tried rust remover and a brush. A little lighter but not much. Rinsed fast so min damage but still remains. So...your suggestion from here?