Have a 4' high crawl space under an L section of the house. The poured slab has a slight slope. I just discovered in a transition point where the footing drops slightly due to the slope they left what must have been a 5 foot long 2x6 on top of the footing before pouring the concrete wall. House is 30 years old. 2x6 has now rotted and outside soil/sand is making it's way in. Should I dig out the rotten wood and fill with hydraulic cement? I read that this type expands when curing. Is this the wrong cement? There is a small crack that goes from this hole up to a foundation vent. Goes through to the outside. Would like to fill hole from inside as there is a patio on outside of wall, footing would be 3.5 feet down. On Cape Cod and it's cold outside!