Preventing Cracks in Concrete Floors with Expansion Joints

You’ve hopefully read our previous post about why we chose to use concrete flooring in our flip and now you have made the decision to incorporate concrete flooring for your house (if you haven’t, check it out here). However, and along the way, you did some more research and realized that concrete flooring needs to be done right in order to prevent it from cracking. This raised a red flag for you and now has you wondering if that’s something you want deal with in the future.

Don’t freak out just yet and walk away from concrete flooring! Let’s go over why concrete floors can crack and what you can do to prevent it.

There are several reasons as to why concrete can crack such as drying shrinkage, excess water, poor sub-grade preparation and improper curing. Outside of these, cracks usually appear in concrete because it is weak in tensile strength. Now, you dotted all your “I’s” and crossed all your “T’s” to make sure that the former reasons listed above are not why your concrete would crack. The latter reason of weakness in tensile strength still needs to be solved and one way to help prevent the cracks due to tensile strength weakness is by using expansion joints (also known as isolation joints).

The tensile stresses that exceed the tensile strength are what causes cracking in concrete. This could be due to fluctuations in humidity, moisture and temperature which cause concrete to expand and shrink, thus causing the tensile stresses. Expansion joints provide relief that is needed and allows the concrete to freely move when it expands or shrinks.

So how and where do you place expansions joints?

First and foremost, expansion joints are placed before you pour your concrete. They are usually placed where a slab of concrete meets a building, wall or another slab of concrete. Pliable material such as asphalt coated, cork or plastic is used for these types of joints. The pliable material should cover the full depth and width of the slab. In the scenario that the concrete floor is an exterior floor, you should seal the joint in order to prevent damage from the elements.

Expansion joints are one of three types of joints that you can use in order to prevent cracking. You can also look into construction joints or contraction joints as a way to prevent cracks. However, a crack here and there is not the end of the world and in our eyes can add some character to the floor. You just want to make sure it’s not a crack that has affected the integrity of the floor and needs to be fixed.