CONCRETE CRACKS

WHY DOES MY DRIVEWAY AND GARAGE FLOOR HAVE CRACKS?

There are two basic reasons why cracks occur in concrete. One is the concrete has cracked due to stress from applied loads and second the concrete has cracked due to the stresses applied to the concrete during the drying process. 

Cracking often occurs when concrete dries and in all probability the cracks you are seeing are from the second reason or shrinkage. Drying shrinkage is an inherent, unavoidable property of concrete and some cracking is normal because of rapid drying or use of a concrete mix that is to wet.  This can cause excessive cracking.  The current builder’s standard is that cracks which are 1/8” or more wide or with 1/8” or more in vertical displacement should be repaired.  The use of expansion or control joints can also assist in managing cracks.

Similar types of cracks can also be found in the interior of the home.  This may be noticeable when pulling up carpet or vinyl flooring.  These cracks, if excessive, can become evident when carpet padding starts to wear down.  Of particular concern are the areas where ceramic tile will be laid.  If proper sub-flooring is not installed ceramic tile may crack due to the concrete slab cracks.

The potential for concrete cracks can be reduced by the proper use of joints.  Large sections of concrete (driveway or slab) should be provided with properly spaced joints.

Control joints, also called contraction joints, are grooved and placed in sidewalks, driveways, or floors so that the cracks will occur in these joints rather than in a random manner.  For a driveway these joints should typically be placed every eight feet.

In addition to control joints, isolation joints are used to separate a concrete slab from other parts of a structure and permit horizontal and vertical movement of the slab. They are placed at the junction of floors with walls, footings, and other points where restrain occurs.