What Do Concrete Cracks Mean?

Identifying concrete cracks and what they mean

Few issues will send homeowners running to contractors faster than cracks in concrete. The bad news is that nearly all concrete will crack at some point. The good news is that cracking rarely indicates a major structural problem. It is important to understand exactly why concrete cracking occurs and when you need to worry. This article will cover the basics of what concrete cracks might mean. However, if you are concerned about cracking in your driveway, patio or foundation, a concrete mason will be the best person to evaluate your specific situation.


The primary reason for concrete cracking is shrinkage during the drying process. This shrinking phenomenon can be compared to a sponge that dries out. What happens? The sponge becomes considerably smaller as the moisture disappears. The same is true of concrete. When the shrinkage occurs, it can put stress on the slab itself. If the tension becomes intense enough, cracks will appear. Some contractors will let clients know up front that this cracking might occur to relieve concerns about the foundation or the concrete surface. Most of these cracks are easy to repair and not much to worry about.

To control where these cracks occur, contractors will often install joints into the concrete. These joints are formed by decreasing the width of the concrete by a precise amount in certain locations along the surface. The addition of isolation joints will ensure the cracking that does occur will make a straight line in predetermined spots. You can see isolations joints along sidewalks, driveways and foundation walls in some cases. Masons may also use material like steel bars or wire mesh to hold concrete particles together in the event cracking does occur.

Thermal Cracking

Thermal movement is another common cause of concrete cracking, especially in larger concrete structures. In this situation, heat rising within the concrete can cause it to expand from below as the surface is cooling and contracting. The pressure placed on the concrete slab during this process can cause cracking. The amount of cracking and the size of the cracks will largely depend on how much of a difference in temperature there is between the inner and the outer concrete. Steel bars or isolation joints can also help to keep thermal cracking to a minimum.

Concrete cracking can be easily repaired in most cases. Homeowners can tackle hairline cracks themselves using a filler substance like epoxy or urethane. Always consult with an expert about the best material to use for repairs if you plan to handle the project yourself. For example, driveway cracks may require epoxy filler with sand while other repairs might require basic epoxy filler or an entirely different treatment.

Larger cracks might mean more extensive repairs. In some cases, additional concrete may need to be poured. Crack injections of polyurethane can be used on poured basement walls to protect the basement from water leaks. For larger projects like this, it is a good idea to hire a concrete mason to ensure the job gets done correctly.