I have a limestone rock basement under a 100 year old house. I am wondering what the best method to getting it waterproof. also, I would like to clean up a couple of walls by covering them. somebody had covered these walls before by spreading what looks like a layer of cement over the top of the rock, which of course didn't adhere well and is loose and cracking off. I am a carpenter with alot of experience in alot of areas, but this ain't one of them!! My plan is to remortar the wall in the areas that the mortar has fallen out or just turned to sand. I will use regular mortar with an additive to help it adhere. Other sections have been remortared with either cement or hydraulic cement. i am guessing it was regular cement because I think the expansion of the hydraulic could cause problems like cracking the rock or shifting it. What advice can you guys give?