This is about basic floor crack problems, cause and effect.
Generally speaking most basement floors and slabs are not structural components, depending on your area and local building codes the basement floors are poured over soil without reinforcement. The concrete thickness may also very from area to area and be as little as 2 inches thick. It is very to have cracks in your basement floor and most are not structural issues many factors come into play to be the cause of settling ,cracking and floor heaving.
The most common problem with basement floors is the moisture or the water level beneath the floor, if the water level below the floor is allowed to saturate any Clay or soil below the slab this can cause the soil to swell and cause the to heave up. Water levels below basement floors if not controlled by weeping tile or drainage systems can also cause corrosion under slabs and footings, it is very common for a homeowner to look for a solution for basement floor cracks without solving the real problem.
Factors to consider when dealing with floor cracks:
1. Does the foundation have a working weeping tile or drainage system.
A working weeping tile system is very important to help control water level be for it gets under the slab, some older houses used clay drain tiles that over time have collapsed or been crushed from settling and some even older houses have no drain tile system of any kind. Typically houses with a drain tile system will have a trap or a cleanout that can be inspected to make sure that the back flow preventer valve is not simply stuck shut . New houses can also have problems from poorly installed weeping tile to weeping tile that has been crushed by the backfill during construction and another issue with some new houses built in a hurry that the weeping tile was simply not installed deep enough.
2. At times does the water level under the slab come near the surface level of basement floor.
Water level under basement floors that have poor drainage weeping tiles or a sump pump that the level is set too high will allow the water during storms or spring melt to overwhelm the sump pump and allow the water level rise just below the poured concrete. Water levels this high can have the effect of swelling the soil and up heaving the concrete floor and making it appear that water is coming from the perimeter of the foundation.
3. How thick is the floor?
The thickness of the floor can also have it affect on how easily the slab cracks, a lot of older homes built before any building codes can be suspect of thin floors, a lot of earlier homes had dirt floor basements then later on basement floors were poured. Some issues can arise during construction where the soil underneath was not leveled and when the concrete was poured some of the areas end up thin. Generally speaking any cracking in the slab floors would be established in the first three years and any drainage issues will make the cracks show up in the years after.
4. Was the basement floor or footings poured in the winter season?
Construction and winter in the northern climates can cause problems with the foundation and slabs, if during construction the soil beneath the footings is allowed to freeze it may swell and during spring melt or when the building is heated the footings and the slab may sink or shift.
So before deciding to repair any cracks in the slab the homeowner should check to make sure the weeping tile system is draining and if possible check the water or moisture level below the slab. Sump pump's should be set as low as possible as to keep the soil just beneath the slab as dry as possible. Sump pumps should attempt to keep the water level at least 12 inches below the slab level.
If you are dealing with the structure that has no drain or weeping tile system and only a sump you may have little or no control during storms or spring melt to control the water level under the slab for future heaving.