Cracks In Custom Home Slabs

Cracks In Concrete

A question that drives Builders crazy, why are there cracks in the concrete  slab of my custom built home?

Consumers with little home building experience usually ask this question. It's many times delivered with an accusatory tone, as though the Builder has provided an inferior product. It's almost as though some people think, you can judge how good a Builder is by the number of cracks in a concrete slab.

Hairline cracks in concrete have absolutely nothing to do with how good a Builder is. The short answer, concretes natural tendency is to crack into squares.

A good Builder can look at a set of building plans and predict where the concrete slab is going to crack even before the concrete is poured!

Don't believe me? Next time you go for a walk in your subdivision look at the sidewalk. Public walks are usually 4' wide with a tooled control joint every 4' in length, notice you don't see many cracks in the sidewalk either. That's because the concrete finisher struck a tooled, control joint 1" deep into the concrete walkway. Striking that control joint 1\4 of the 4" concrete walks depth is the secret. The finisher knows the concrete is going to crack every 4' so he is providing a pathway for the crack to follow where it will be less noticeable, in the control joint.

The lesson here, concrete cracks in squares. A house slab with an irregular shape will have a tendency to crack in squares too.

So how do Quality Builders manage the cracks that naturally occur in house slabs? 

With carpet and hardwood areas, cracks less than 1/4" wide are not normally an issue. There is a waterproof membrane under the slab to stop water intrusion and the top side is covered with a flexible material like carpet. 

The slab areas that require special attention are places where tile or stone is placed on top. Quality Builders, install an isolating membrane that separates the hard surface materials from the slab concrete. They do this instead of adhering hard surface materials to the building slab.  This way, any obvious cracks or ones that may develop in the future will not telegraph from the slab through the tile or stone. This is an important quality feature that will be important to you as the consumer over the years. 

Being proactive during the building process will minimize any future cracks that may appear in tile and stone grout joints or through the hard surface material itself.