What Do Horizontal Cracks in a Brick Wall of a New House With a Post Tension Slab Mean?

Post-Tension Slabs

• Concrete slabs act as a foundation material for home and building construction projects. Post-tension slabs include an embedded network of steel strands that form a structural framework for the concrete as it dries. Each strand end attaches to an anchor that works to hold the strand in place and maintain its tension within the concrete slab. In effect, steel strands function as tendons that compress the concrete and prevent it from cracking or breaking. Proper foundation design ensures post-tension slabs hold up over the years. When improperly designed, gaps and cracks may form along a home’s exterior and interior walls.

Differential Movements

• A newly constructed home should show no signs of wear and tear, so cracks along a brick wall may warrant cause for concern. Horizontal cracks, in particular often indicate problems further down the wall where the foundation begins. Differential movements along the foundation involve shifting soil layers that push foundation walls inward. When this happens, horizontal cracks appear further up on the wall as a result of the pressure exerted against the foundation. Since the greatest amount of pressure exists around the foundation portion of the wall, horizontal cracks appear in areas where the structure of a brick wall has shifted.

Earth Settlement

• When laying a post-tension slab foundation, moisture levels in the soil can affect how a home or building settles once the moisture evaporates. Moisture levels also determine soil compaction and soil erosion rates, which affect how a foundation sits or settles. Laying a post-tension slab foundation on top of moisture-laden soil can cause the foundation to shift once water evaporates from soil layers. In effect, the highest evaporation rates occur along the edges of a foundation slab where direct exposure to air and wind occurs. This can cause slab edges to buckle as perimeter soil layers settle. When this happens, horizontal cracks may begin to form along the brick walls of a newly constructed home.

Slab Lift

• Slab lift has to do with soil moisture increases that take place after laying a post-tension slab. Slab lift can occur when laying foundation structures on dry soil layers that later take on water and moisture. Water and moisture changes can result from groundwater levels that rise from the effects of heavy rains or snow. Faulty drainage systems can also cause groundwater levels to increase over time. Under these conditions, a post-tension slab may lift up in areas where the soil has expanded and cause the weight of the house to shift. Much like the effects from earth settlement, the pressure of the weight shifts can cause horizontal cracks to form along brick walls.