When we are called in to perform a basement inspection, one of the first things we look for are cracks in the foundation. We find these to be more common in older structures, but also are finding cracks in newer homes where the concrete may not settle properly due to the soil freezing and thawing, contracting and expanding.
What Are Foundation Cracks?
A foundation crack can occur for many reasons. Poor construction, soil condition/settlements, or an act of god [earthquake/frost quake], any of these can cause stress on a foundation wall. Repairing a crack depends on the type of foundation wall and cause of the crack.
How Do Foundation Cracks Occur?
Cracks can occur in different ways: High water tables, saturated soils, extreme dry days, or just natural settlement where the soil just settles under your house. Depending on your area and the soil conditions, when an extreme amount of rain occurs, the water table can rise which can cause pressure under your house, and when the water table lowers so does your house. This creates stress to the foundation and the entire house itself. Saturated soils can expand, which puts pressure on your walls, and can even settle the house. These areas usually have a lot of clay or sand. On extreme dry days, the soil contracts and your home can settle too.
Extreme weather conditions, bad concrete mix, bad backfilling and equipment damage can be the culprit to your foundation crack. Extreme weather conditions entail hot and/or cold temperatures. When pouring a cement wall extreme cold weather can freeze the water in the cement allowing it to expand where extreme hot weather dries the cement too fast and shrinks rapidly. This rapid expansion and compression can crack the cement, especially if there was a bad mix prior to pouring and the concrete mix had too much water. If the cement doesn’t dry properly, it is fragile and likely to crack.
Backfilling when the concrete is still soft is another way the wall cracks. Equipment damage and bad backfilling can happen when the driver is too rough or the machine is too big and accidentally hits the side of the foundation. Big boulders or large debris can hit the foundation wall damaging the foundation.
Act of God
This is something that no one can control and can create more cracks or open existing cracks up more. Earthquakes, are not common and can cause major damage. Frost quakes, on the other hand, occur when a large volume of water is accumulated in the soil or bedrock and freezes due to a sudden temperature drop. This quick flash freeze puts pressure and stress on its surroundings. The pressure builds up until the ground cracks and gives out an explosive sound.
Foundation Wall Cracks
Cracks in foundation walls can be caused either by the natural settlement of your home or poor construction practices, causing shrinkage in your concrete foundation wall. In either case, an inlet for water is created. This can cause serious damage and become larger over time due to freeze and thaw cycles allowing ice in this void.
Foundation cracks can be fixed either from the inside using an epoxy injection method or from the outside, digging down to the footing of the foundation, sealing water out using rubberized urethane. A drainage board is added to enhance the drainage process and move water away from the crack. Either repair method should be considered as quickly as possible to prevent further damage to your home.
Cracks occurring in basement floor slabs can typically occur over time due to the settling of the building, poor sub-surface drainage, and concrete shrinkage.
Leaks coming up through the floor are consistent with older homes because the building techniques usually did not specify a substantial amount of gravel to be placed below the floor slab. Also, floor slabs were not poured as thick and years of coming into contact with ground water can exaggerate the problem because of erosion, further thinning out the slab.
Having gravel below the floor is important to create a capillary break between the existing soil that the home is sitting on, and the concrete floor. If there is little or no gravel, a remedy to this groundwater issue is to break up arteries or shallow trenches into the floor which lead into a point of drainage and install weeping tile with gravel, topped with concrete to match the existing floor. Ground water that is rising will find its way into these pathways and relieve pressure pushing upwards through the slab.
How Do Concrete Foundation Cracks Occur?
Concrete foundation cracks occur at any angle, as it’s a solid wall. This type of track typically occurs within 30 days of the concrete curing process. Usually a very simple repair. However, in combination with “other signs” could be a more serious sign of settlement issues and could mean there will likely be more cracks to repair.
Vertical cracks are very common in every foundation wall. Most cracks derive from the corners of windows and doors, starting from the top and tapers inwards towards the bottom. Once the vertical crack is chipped out, it is parged with industrial strength hydraulic cement and waterproofed.
Something as small as a hairline type of crack can be waterproofed. Anything bigger may require a structural engineer to be called in before any repair work is done.
The location of the horizontal crack depends on the problem. A horizontal crack at the bottom of the wall near the floor means the wall’s structural integrity has been undermined due to the water table rising/lowering the house; Or extreme dry days allowing the soil to dry out and shrink settling the house.
Horizontal cracks at the top of the wall are from the winter weather and spring thaw cycle. The soil expands and contracts and puts pressure on the wall. Clay soil condition is a major culprit as it acts like a spunge.
Horizontal cracks are often a sign of a structural problem that needs to be assessed by a structural engineer prior to waterproofing.
During the construction process, a metal rod is used to hold 2 plywood forms together to pour concrete between them. When cured the rods are then cut or removed and parged over with hydraulic cement which may break down over time and allow water to leak in through the rod holes in the foundation.
Concrete honeycombing is the result of imperfections or voids in the concrete revealing a rough/stony surface after the foundation wall has been cured and the forming been removed. Depending on the depth, the honeycomb can be chipped out until a solid sound concrete wall is exposed. It can then be patched with mortar, hydraulic cement, or other cement based that will match the color of the cement wall.