We often get asked about the causes behind concrete cracks. Customers wonder why they can appear even in a newly poured foundation. A homeowner will question why it is cracking and wonder if they received substandard workmanship or products.
When installed properly, concrete is one of the most durable and long lasting products you can use around your home. But it is important that concrete contractors follow well-established guidelines with respect to concrete placement. Durable, high strength and crack resistant concrete does not happen by accident.
Often we see simple settlement cracks. As durable as concrete is once cured, it’s hard to find a basement that doesn’t have at least one crack in it.
Why Concrete Cracks
1. Excess water in the mix
Concrete does not require much water to achieve maximum strength, however, a much of concrete used in residential pours tends to have too much water added to the concrete on the job site. This water is added to make the concrete easier to install. This excess water will however, greatly reduce the strength of the concrete.
Shrinkage is another common reason for cracking. As concrete hardens and dries it shrinks. This is due to the evaporation of excess mixing water. The wetter or soupier the concrete mix, the greater the shrinkage will be.
2. Concrete drying too fast
Rapid drying of the slab will significantly increase the possibility of cracking. The chemical reaction, which causes concrete to go from the liquid or plastic state (or a solid state), requires water. This chemical reaction, or hydration, continues to occur for days and weeks after you pour the concrete.
3. Improper strength concrete poured on the job
4. Lack of control joints (in concrete slab).
In a concrete slab, control joints help concrete crack where you want it to. The joints should be of the depth of the slab and no more than 2-3 times (in feet) of the thickness of the concrete (in inches). So 4″concrete should have joints 8-12′ apart.
5. Foundations poured in the winter
Foundations poured during cold months, or poured foundations that are left unheated during the cold winter months will develop many more cracks. Foundations poured on a base (ground) that is improperly compacted will inevitably develop more cracks as well.