How to Repair and Level a House's Foundation

Drill several holes in the foundation floor slab. If the slab is thick, more than 4 inches, then more holes can and should be dug. Normally, holes for a normal sized basement are about 1 inch in diameter, spaced about 6 feet apart. Depending on the size of the basement, two holes for pumping the grout is sufficient. If the entire side of the house is sinking, then three holes forming a triangle on that side of the house will do it. Since any high quality grouting material is designed to spread under the slab, the fewer holes the better. For most jobs, two is probably sufficient. Drill only on that side of the house that is sinking and needs to be raised. In general, a gas powered percussion drill is used, with a 4-point bit. Make certain that the hole is large enough for the pumping mechanism to penetrate under the floor.

Prepare the grouting material with consistent mixing. Make sure there are no lumps in the material. It needs to be smooth and consistent. Normally, you will hire a company that will mix and prepare the grout for you. The quality of the equipment here is crucial. The more severe the foundation slump, the heavier grout you will need. Medium strength grout uses about 10 percent cement, while stronger materials will use 20 percent, maybe a bit more. The remainder of the material is sand and water. Additives, like expanding chemicals, should be used for foundations that are severely sunk. Additives like Bentonite are occasionally used to increase the expanding power of the grout for heavier or larger houses.

Pump the mixture into the hole closest to the sagging part of the foundation. The pump should be, at a minimum, capable of pushing the grout at 110 cubic feet per hour. This is a heavy duty piece of machinery and should be worked on with care.

Reseal the holes with a highly rated polyethylene coat. In some cases, a polyurethane coating will do as well. This is something that you will want to check on at least daily in the first few weeks.