Hi I have a 70’s town house that I am currently renovating. The ground floor floor boards batoned onto a concrete screed about 50mm deep. The soil stack runs internally from the rear corner of the property to the front. There is a 9-12 inch square break in the screed around where the soil stack runs under the ground floor screed. Here there is nothing but loose dirt and sand and the overall level is about 2-4 inches below the level of the screed. I am assuming there is no damp proofing at this point. Is there anyway to repair this patch around the soil stack to bring the level up to the rest of the floor screed. I wish to do this without causing any damp issues by just chucking some cement/mortar down the hole, which I am guessing will lead to some sort of rising damp. Is there anything I could use instead of basic mortar? Epoxy mortar, tanking slurry, waterproof render? Any ideas appreciated. Thanks Steve