The Cause of Cracks in Poured Walls

Drying Shrinkage

• After you pour the concrete into the form, it may lose water and shrink while it is still setting. According to the CFA, a 10-foot long piece of poured concrete loses about 1/16 inch of length as it dries. Because the part of the concrete near the surface shrinks faster than the inner part, cracks form in the surface, especially if the conditions when the poured concrete sets are windy, dry and hot.

Load Stress

• Cracks may appear because the poured walls support weights that are heavier than they can safely withstand. For example, there may be heavy machinery placed right against the building foundation. If this happens, you may see cracks forming along a horizontal line. According to the CFA, these cracks usually appear about 16 to 48 inches down from the top of the poured walls.

Settlement

• Settlement refers to the process by which a building structure sinks lower into the ground. This may happen if the soil beneath the building loses moisture and shrinks, or if the contractor failed to compact the soil before laying the foundation. It may also happen if the soil contains too much organic material, which decays and leaves voids. Settlement cracks stretch diagonally across the height of the wall. If you see such cracks, consult a structural engineer for advice.

Other Causes

• If you live in a cold area, the concrete may freeze in the winter, then thaw when it gets warmer. As the concrete expands and contracts multiple times, cracks may form. These cracks usually don't appear soon after pouring the concrete. Cracks that appear years after the concrete dries may also be due to corrosion of the reinforcing steel in the concrete and exposure to sulfates. However, these factors rarely cause cracks, especially if the poured wall is of good quality.