Tips to Avoid Cracks in Concrete

It has been my experience that there are two kinds of concrete: concrete that is cracked and concrete that will crack at a later time. However, there are ways to minimize the occurrence of cracking concrete.

Cracks in concrete driveways are common and can lead to water transferring through to the soil that bears the weight of the slab. The water can cause additional settling of fill and increase the size of the opening in the crack as the slab loses bearing on the fill, thus more water transfer, settling more fill, etc.

To minimize the cracks when initially placing the concrete, control joints are critical. As a rule of thumb, there will be no more than 100 square feet of unjointed area. Control joints can be placed with different methods. Some use ¾” wide pressure-treated wood, others will sawcut a 3/16” groove on a layout that can be adjusted to accommodate the project design. The sawcut joint will be approximately 1” deep, and can be cut using a hand held saw with a diamond blade or a walk behind power saw.

Welded wire reinforcing mesh or “re-mesh” can be used in the placement of the wet concrete to add structural strength. The re-mesh can hold the cured concrete together even when cracks occur. The use of a “fiber” or chopped strand fiberglass, can be added in the batching process of the wet mix before placing. The fiber also strengthens the cured material.

Many overlay systems are marketed to restore the beauty of the surface or to decorate old concrete that has cracked and become unattractive. Not a lot can be done to repair a crack unless the control joint rule of thumb is followed. If the original installation did not include sufficient control joints, they can be cut and the existing cracks filled with epoxy before the overlay is installed, however this may not offer a long term solution.

Interior concrete can be installed with control joints as well. A barrier material can be installed for underlayment before finish flooring materials such as tile or wood. A random crack in an interior slab can reproduce itself on the finish side of tile or stone especially if no crack barrier underlayment is used.

Exterior concrete flatwork with control joints can be maintained by applying sealant (preferably urethane based) in the joint opening to decrease any water transfer through the slab. Pitching the concrete to drain and not pond is also recommended and should be designed before the concrete is placed. Existing grades may be altered to allow proper and sufficient watershed when the concrete is installed.

In summary, the most important decisions in the concrete installation will be made BEFORE the pour is scheduled. A professional should be consulted about grade, control joints, finish, re-mesh, fiber, aggregate, water in the mix during batching, water added to the mix on site and methods of placing and finishing the material.