Concrete Blocks & Foundation Movement

Causes

• Foundation movement most often comes from soil and water pressure. The former is the weight of the soil against the walls of the foundation. The latter is called hydrostatic pressure, and refers to the weight of water against the walls. The latter can be dealt with effectively through outdoor drainage systems and a “controlled leakage” through deliberately drilled holes in the wall that can relieve some water pressure. Another central cause of damage to cinder block walls comes from freeze-thaw movement. In this case, the constant contraction and expansion of both blocks and soils under changing weather conditions can cause foundation movement. Concrete blocks are the most vulnerable because they are pieces that are mortared together. A solid, poured wall is much stronger against this pressure.

Cinder Blocks

• Cinder or cement blocks are an inexpensive, but potentially unstable foundation materials. If the walls are under enough pressure, the blocks are always vulnerable at their mortar joints. These are the first to move or crack under pressure. Most state and local codes require an iron bar, called a rebar, placed vertically through the block. The blocks themselves have two hollow cells, and when these are placed into the foundation, they are filled with concrete. The rebar is then rammed through the holes that will be held in place by the concrete. Blocks without the rebar are far more vulnerable than those without.

Types of Cracks

• Foundation movement leads to the cracking of the foundation structure. A horizontal crack, especially if it follows a pattern connecting to the floor, suggests very dangerous condition. Horizontal cracks are always more serious than vertical ones. The horizontal crack implies foundational movement and a growing lack of integrity in the structure. Vertical cracks are almost always less serious and often come from settling or the drying of concrete. Horizontal cracks usually come from foundation movement. Other than the mortar joints, the most vulnerable part of the wall is its very center. This means that foundation movement will affect a block wall at its central part, according to the cut of the joints. These are the most common causes of leaks and structural disequilibrium.

Results

• Foundation movement can lead both to cracks as well as bulging and buckling. A bulging block foundation demands immediate action. The bulge often derives from temperature shifts, where the blocks begin to weaken because of many seasons of freezing and thawing. This is the block's worst enemy and cause, over time, the worst damage. Usually, blocks reinforced with a rebar are far less vulnerable to this, yet it does occur. If the block foundation wall is attached to the floor, then any movement in the foundation will lead to a “leaning” of the wall at its topmost parts. This can be identified by an “overhang” of the upper bricks sticking out from the lower ones.