Concrete Block Foundation: Repair a Bowing Base
Performing a concrete block foundation repair on a bowing foundation can be both dangerous and expensive. The bowing in a concrete block foundation is generally caused by outside pressure from soil and water as they expand and contract during seasonal freeze/thaw cycles. Cracking in basement walls is usually an early indicator that the foundation is beginning to bow. The most surefire way to fix this problem is to jack the floor up, excavate the ground around the foundation, and rebuild the wall. The process is inconvenient, expensive and time consuming. However, if the problem is caught early enough, performing some of the actions below may fix the problem.
Fill the Foundation
Only attempt this foundation repair method if the inside wall of the foundation is dry and the bulge in the wall does not deviate more than 1 inch from being plumb. This method involves cutting the faces off the blocks near ground level on the exterior of the house with a concrete saw. Within the blocks are round hollow cores. The homeowner then fills these cores with wet concrete. Into this wet concrete #3 steel rebar is pushed all the way down to the footings. This process should be repeated for each block along the wall or, at minimum, every 48 inches. When the concrete has set, the faces on the outside blocks are replaced using any concrete that is left over.
Ensure there is No Lateral Movement
If the foundation is filled, the lateral movement of the wall must also be arrested. Newer houses will have a mudsill along the top of the interior portion of the wall that will do this. If the house is older, a piece of wood that is at least 2 inches by 6 inches can be nailed to the underside of the joists to keep the wall from bending or sliding forward. Similarly, on the bottom of the wall a support can be anchored to the concrete slab of the floor, unless the foundation wall was installed without any expansion foam beneath it. In this case, the floor slab itself will keep the wall from sliding.
Brace the Wall from Within With Support Beams
Some people prefer to brace a bowing foundation from within. Like other foundation repair methods, this method should probably not be attempted unless the wall is dry and no more than 1 inch from plumb. When bracing a wall from the inside, homeowners usually use steel I-beams. The beams should measure no less than 2 inches wide, 3 inches deep, and should have walls at least 5/16 of an inch thick to be strong enough for the job. People who attempt to fix their foundation this way place the beams against the wall and bolt them through the joists above. The beams cannot be more than 48 inches apart. If the joists run parallel to the wall, a notched 2 inch by 8 inch board is usually connected to the joists perpendicularly. These perpendicular boards must span at least two joist bays. The I-beams are bolted to these boards for support.
Anchor the Beams
Those who use bracing I-beams always anchor them to the slab floor. A bolt is run through a plate that is welded to the bottom of the beams and down into holes in the concrete. The Holes are predrilled in order to properly anchor the bolts.
Fill the Spaces
To keep a braced bowing wall from moving inward any more than it already has, the spaces between the beams and the wall are generally filled up with mortar grout.