Below grade leaks require 3 things:
Since at least Roman times, we have known to:
1) Keep water away from the building with proper site grading, proper rainwater runoff control from off the building
2) Assume all of your efforts to keep water away from the building have failed and then limit the ability of the water to penetrate the building by using clay caps and other impermeable materials adjacent to the building and controlling hydrostatic pressure below grade against the building
We believe the most robust approach relies, not on eliminating all the holes but eliminating the force the pushes the water through them. The weight of the water is that force. We measure the weight of water with...water. Ok, water column. 1 inch of water weighs 1 inch water column (WC). To make this more complicated, 1 inch of water = 250 Pascals (Pa). Pascal is French. Naturally, the English came up with their own measurement system: Newtons per square meter. Anyway, 250 Pa, is equal to a 70 MPH wind! That's just 1 inch of water on your foundation. But you can literally have many inches of water against your foundation.
So, free-draining material is used to reduce hydrostatic pressure. Rocks and sand traditionally allow the water to drain away from the foundation to a perimeter drain and we eliminate the force or #3 above so, no leak!. We can also layer drainage board or other mats with big dimples around the foundation to accomplish the same thing. Drainage mats with big, Cary Grant-style dimples also provide a capillary break for the foundation.
Again, we focus our efforts on eliminating this force because we don't think we can eliminate the holes in a porous material like concrete that is also prone to cracking and as we stated above, we assume all of our site grading and proper rainwater runoff efforts will fail. Ask us why we assume that...:)
So, use materials that: Span the cracks. Control hydrostatic pressure. Provide a capillary break. You won't be sorry.
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