Concrete block was used extensively for foundation construction in the mid 1900’s. The primary problem we see with block foundation walls is inward bowing of the wall and cracking of the mortar joints.
Concrete block foundation walls which are tall enough to form basements, and are constructed in clay soils (very common in northern Illinois), generally do not have the strength to resist the forces of lateral soil pressure unless they are grouted solid and reinforced with steel bars. Unfortunately, most homes built in this area with block foundation walls in the mid 1900’s were not built with any type of grouting or reinforcement. Over time the pressure of the soil acting against the foundation wall forces it inward causing the walls to crack and bow. The integrity of the block foundation wall continues to degrade the further it is pushed in as more and more cracks develop between the block joints. And as the wall is forced inward, the weight of the home above the foundations accelerates the inward bowing process. If the situation is not stabilized early on in this process, the walls will continue to move inward and the mortar joints will continue to crack and deteriorate.
The lateral earth pressure increases significantly as the depth of the basement increases or as the soil becomes saturated with water. With older concrete block foundation walls the problem is made worse as perimeter drain tiles were rarely installed. This is usually evident as the basement area may be wet.
The service life of bowed masonry foundation walls can usually be extended by stabilizing them if there are not a significant number of cracks in the mortar joints. The most economical and effective way to stabilize a masonry wall is done with vertical braces in the form of vertical steel beams. Tie backs when used alone are generally not effective as the concrete blocks in the area of the tie back will fail as the rest of the wall continues to move inward. Tie backs are effective when they incorporate a vertical steel beam to the inside of the foundation which engages the entire height of the foundation wall.
The vertical braces rely on the masonry foundation walls having enough integrity to resist the soil pressure and span from bracing beam to bracing beam. If the foundation wall is bowed inward more than approximately 1-1/2″, and a significant number of the mortar joints are cracked and deteriorated, the then the foundation may have to be replaced or reinforced with a new concrete wall in front of it. Unfortunately bracing the foundation wall with vertical steel beams is not a viable option as the wall will continue to bow and crack between the vertical braces.