How to Raise a Sunken Foundation

Drill a hole into the basement floor. This hole is generally no wider than 1 5/8 of an inch. The hole cannot be too large, or the structure of the basement floor will be compromised. The holes should be no more than 5 feet apart.

Break the joints of the basement floor to the walls or other structures of the house. If it is just the floor that is sinking, the floor cannot be connected to anything. This is not relevant if the side of the house is sinking, since the whole structure can be leveled this way. The larger and heavier the house, the less relevant the slab-jacking method is.

Pump the material into the hole. The pump needs to be a dual-action pump that will not allow any back splash of material up through the hole. This requires the pump to be roughly 1,000 pounds per square inch in strength to properly force the material into the ground. The material itself is often a mortar mix that is lighter than cement, but will provide a sturdy base that will give the foundation more support.

Pump closed cell polymer foam into the ground for larger or more severe jobs. For foundations that have sunk, the more expensive, but more effective, foam system can serve to both raise the house and create a stronger foundation than the simple mortar. This may also work for larger houses. For small ranch-houses with a slab foundation or shallow crawlspace, this might be ideal. The foam is designed to inch its way through the underlying soils. It fills even the tiniest void, re-creating the soil underneath the house. The foam also expands, giving the foundation an added lift that levels the entire structure. In addition, the foam will provide added insulation and negate the effects of an over-saturated soil structure that causes most foundation sag.

Seal the hole with waterproof polyurethane or comparable material to ensure the material does not rise back onto the floor. This also ensures that no water will penetrate the floor and flood the basement.