How to Waterproof the Exterior Foundation of a House

The foundation is the most important part of the house, and wet foundations eventually fail. Concrete isn't waterproof; it's porous. Water vapor can penetrate unsealed concrete, and liquid water can seep through cracks and joints. Keeping the foundation dry requires moving water away from its base and the surface level and applying a below-grade waterproofing product to seal the walls. There are various waterproofing products on the market, and many aren't guaranteed unless a certified applicator does the work. Choose the product carefully, according to local conditions; there aren't any second chances once the wall is back-filled.

Push broom
Propane torch
Propane tank, 20 pounds
Long-handled ice breaker
Masonry hammer
Blow torch
Reciprocating saw
Non-shrink grout or patching cement.
Trowel-grade mastic
Chalk
Waterproofing product
Spray, roller, or trowel (for liquid or sheet membrane waterproofing)
Long-handled brush and acrylic additive (for cementitious waterproofing)

Instructions

- 1
  Dry the footings with a propane torch. Sweep any standing water away and dry the area with the torch.
- 2
  Break off the form ties on the inside and outside of the foundation. Cut those that won't break off flush with the blow torch or a reciprocating saw.
- 3
  Scrape any loose and excess material from walls and footings with an ice breaker and masonry hammer. Machine-grind any ridges or protrusions as required by the waterproofing product's manufacturer. Sweep the walls and footings until there is no film of dust.
- 4
  Patch or fill large voids and honeycombed areas with non-shrink grout or patching cement. Use trowel-grade mastic for small voids and form tie holes.
- 5
  Mark the extent of the waterproofing with chalk. Stop waterproofing at least 6 inches below the top of the foundation or as close to finish grade as possible. Waterproof any wall that has earth on one side and livable space on the other. Extend the waterproofing 12 inches on an intersecting wall that won't be waterproofed.
- 6
  Apply the waterproofing product with strict attention to the manufacturer's instructions. Ensure that the foundation is completely sealed, with either tight lap joints or a continuous seamless seal, depending on the product type. Back-fill to no more than 8 inches from the top of the wall.

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