Although many concrete problems are caused by the force of expansive soils and soil that settles and/or shifts after a building is completed, it's not always accurate to blame site conditions for cracked or settled concrete foundations.
Sometimes these problems are caused by mistakes made during the construction process.
The outcome is still the same: The services of an experienced foundation repair contractor are needed to correct the problem and complete the foundation repair work.
But it's helpful to understand that concrete problems can originate when the building was under construction.
Here are some of the more common construction-related issues that can cause foundation problems.
Too much rain You dig a big hole for the foundation and set up the forms for poured concrete footings.
Then it starts to rain.
If the soil gets muddy and/or washes away from around and under the forms, you've got conditions that will compromise footing stability and possibly cause cracks and settling in the future.
The same risks apply if there's a lot of rain before wall forms are filled with concrete.
Foundation contractors are supposed to wait for the soil to dry out and correct washouts before a pour, but sometimes this doesn't happen.
Substandard reinforcement Concrete footings and walls need the extra strength provided by reinforcing steel rods (rebar).
Building codes establish minimum standards for steel reinforcement (spacing, size and location of rebar), and an engineered foundation will have even more steel.
If the concrete isn't properly reinforced for some reason, it will crack and shift more easily when soil settlement or pressure occurs.
Inadequate vibration When concrete is poured into wall forms, it needs to be vibrated using a special power tool so that it will flow fully into all areas of the formwork.
Without proper vibrating, air pockets can remain as the concrete cures, creating voids that become weak points in the wall.
Bad mix Ideally, the foundation contractor and the concrete plant crew chief will collaborate to make sure that the concrete delivered to the building site has the right qualities.
The concrete mix should be "tuned" to suit the temperature and weather conditions and the size and design of the foundation.
Many mix factors come into play, including the thickness or slump of the mix, the ratio of cement to aggregate, and the use of admixtures to retard or accelerate hydration, control shrinkage and tolerate freezing temperatures.
A bad mix often means weak concrete that will require foundation stabilization work in the future.
Uncontrolled curing In warm weather, it's often necessary to mist the concrete with water and keep it covered so that it doesn't dry too quickly.
When concrete cures too quickly, it can crack and weaken.
Freezing Special aerated concrete must be used when pouring concrete in freezing temperatures.
If this doesn't happen, the expansive force of freezing water will cause cracks and weakening as the concrete cures.
Backfilling too soon The excavation for a poured concrete wall shouldn't be filled with soil (backfilled) until the first floor has been framed and the concrete is strong enough to withstand the weight of the soil.
Backfilling too soon can cause a foundation wall to crack and bow inward.