What Causes Cracking in Foundation Walls?
Maybe you read our article about cracked concrete. Maybe you’re looking at buying an older house and you’ve been told to budget for foundation wall bracing. Maybe you’ve noticed that that concrete wall in the furnace room isn’t looking as good as it once did. Whatever has brought you here, it has left you wondering, "what causes cracking in foundation walls?"
Typically, there are two main causes of concrete foundation wall cracking:
the weight of soil; and
the movement of soil.
Weight of Soil
Foundation walls aren’t just basement walls that hold up your house: they also act as a retaining wall to hold back soil. Soil, like water, increases its applied pressure with depth. Therefore, the deeper your basement extends below grade, the more weight your foundation walls have to hold back.
Further, wet soil is heavier than dry soil. You may have heard before that it’s important to slope your yard away from your house. You may have also heard that you should have a shallow layer of clay (a clay cap) right against your house. This ensures that as much water as possible can run overland away from your house before it infiltrates the soil. In turn, this reduces the amount of water directly against your foundation wall that becomes saturated.
If you’re from the Regina area, you’ve probably heard of Regina Gumbo: a highly reactive clayey soil. This soil is capable of retaining a high quantity of water and it is highly expansive. This combination creates a soil that is not only saturated, but also exerts extra forces on your foundation walls when it expands.
If heavy, saturated soil puts pressure on your foundation walls over an extended period of time, it may begin to cause bowing in your foundation walls: the mid-height of the wall will start deflecting inward. This may also begin to cause horizontal cracking. Both instances are signs that your wall is losing its resistance to overcome the soil pressure.
Movement of Soil
Another cause of cracking in foundation walls is due to vertical movement of soil. If your building is supported on a spread footing, then it is counting on the bearing capacity of the soil to keep it in place. What is bearing capacity? In this instance, it is the ability of the soil to support a load on top of it without settling or compressing.
Typically, a spread footing foundation should be constructed on native, undisturbed soil that has not been allowed to freeze during construction. However, a weak point could occur in the soil if it was disturbed soil that wasn't properly compacted or if the soil became saturated and the fine materials within the soil are washed away. A weak point could also be caused by organic material or an anomaly in the soil profile.
In this instance, localized failure could occur, causing the concrete footing to settle in one area where the rest of the footing is not settling.
Alternatively, if the soil below the footing becomes saturated and/or if it freezes, it could cause the soil to expand. In turn, this could cause heaving of soil under the spread footing.
If settlement and/or heaving occur below a footing, it causes differential movement: there is now a vertical invisible line running up the footing and the foundation wall that separates two areas that are moving in different directions and/or at different speeds. Now, hopefully this line remains invisible. Such movement adds stress to the foundation wall and over time can cause vertical cracking.
Has this article raised more questions than it's answered? Do you have questions or concerns about your foundation walls? Feel free to give us a call or send us an email!