What causes a horizontal foundation crack in concrete and is it serious?
As we have discussed before, concrete cracking is not abnormal. Cracks can range from hairline, with only cosmetic defects to large multi-inch wide structural cracks. These large cracks usually indicate foundation failure and require immediate repair.
A recent repair call in Richmond Kentucky today highlights some of the challenges in diagnosing the cause of a foundation concrete crack. We were called to evaluate a small wall that has a long horizontal crack. The wall is located in the basement with the front partially exposed and connected to the floor slab. The back is set against soil and a slab that is outside. To the left is a masonry block wall and on the right a brick column, foundation masonry.
(Editor Notes: pictures were taken in a dark basement, an app was used to brighten them)
The crack is large, approximately 2″ at the widest point. As we take observations of the wall, we notice honeycomb sections, aggregate pop, delamination and discoloration. The wall serves as a way to hold back soil with no dead load.
Honeycombing refers to voids or cavities that are left in the hardened concrete due to incomplete filling of the formwork or improper compaction of the concrete
Aggregate popout is small, generally cone-shaped cavity in a concrete surface left after a near-surface aggregate particle has expanded and fractured.
Concrete delamination is when the top or outermost layer of a concrete structure detaches exposing the aggregate underneath. This is caused by incorrect finishing, or inconsistent materials.
Discoloration is when the concrete surface appears patchy. Efflorescence is a white, chalky, or powdery deposit that forms on concrete when moisture causes soluble salts to rise to the surface.
What could cause this type of issue?
In short, there are many variables that can determine why this happens. Let’s take a look at those causes and if they apply here.
The crack runs right through where the delaminations and honeycombing occurred weakening the surface. The delaminations here are most likely the result of an incorrect distribution of form release on the form and the surface just peeled off when they were removed. The honeycombing is likely caused by not vibrating the form and the concrete being too watery.
The efflorescence tells us that water has traveled through the crack. The crack is dry and the owner has never observed water leaking but this summer significant water drainage work has occurred.
The concrete wall has no expansion joints at the block or brick walls. Likely the culprit is as the concrete dried, the wall began to contract and expand and cracked at the weakest location. Water from the ground or behind the wall followed the crack making it open and begin to fail.
As general advice, if the crack is greater than a 1/8″, you want to investigate. If this wall carried any load, repair would be necessary.
As an aside, we here at Felice Construction warranty all our work. We offer multi-year guarantees since most issues do not appear till the 1-3 year mark.