Concrete is a commonly used material used in modern home construction. Though it is designed to last for many years, most concrete structures, including basement floors and concrete slabs, can develop cracks. These can be minor cracks, usually due to weather fluctuations or normal home settling, or a large crack that reduces the structural integrity of the home. Depending on the damage, the techniques and costs for repairing them will vary greatly.
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Concrete is primarily a combination of cement, stone and water that can have other components added depending on the needs of the builder. This flexibility -- making it more waterproof, for example -- is one of the reasons it is so popular in construction. Its makeup, however, also makes it fairly rigid, a trait that can be good or bad. When used in home construction, minor cracks may begin to appear in the foundation or basement floor within a few years. These are superficial problems that are usually caused by weather or normal shifting of the home. More serious problems may occur if the slab was poured incorrectly or not supported properly, which can become a costly repair.
Types of Cracks
There are three main types of cracks that occur with a concrete slab. Shrinkage cracks occur when the water used to mix concrete evaporates, causing the slab to shrink. These cracks are rarely a structural concern but may allow moisture into buildings. Settlement cracks occur for a few reasons, including a lack of proper site preparation before the slab was poured. If, for example, a slab sits over large pieces of organic matter, the foundation may begin to sink as this material decays. Improper mixing of concrete or general moisture loss of the soil may also be to blame. Perhaps the most severe damage comes from frost heaves, a problem that occurs when water in soil underneath a slab freezes, causing the soil to expand and forcing concrete outward. This problem occurs primarily in cold climates and can cause irreparable damage to a concrete floor.
Average Cost of Minor Repairs
The cost of repairs is largely based on how severe the damage is and how much labor will be involved in the repair process. For minor surface cracks, such as those caused by shrinkage, a simple concrete overlay can be done to cover them up, creating a more aesthetically pleasing look. The cost of this is minimal if going with a basic overlay, and as of 2011 runs between $3 and $7 per square foot. Another option is to simply fill cracks with a waterproof sealant, which can be purchased from home improvement stores for between $9 and about $20 per bottle.
Average Cost of Major Repairs
A basement floor or foundation that has been severely damaged may require extensive repairs or complete removal and replacement. Both are possible, though they can be extremely costly. Strengthening and stabilizing (underpinning) a floor or slab can be a time-consuming and expensive process. Depending on the amount of damage, these costs will fluctuate greatly. Underpinning one side or corner of a home that has started sinking can start at about $3,500. If a general strengthening or addition is required, that starts at about $300 per square foot. That largest variables are the size of the space and amount of damage that has been done, and, depending on which area of the country, local labor rates may raise prices.