Settling Cracks in Slab Foundation

Settling Cracks

I have a lot of calls and questions from customers that are concerned the home they are interested in purchasing may have structural issues due to cracking seen in the slab of the home, garage, or driveway.  In most cases these are not structural issues, these are settling cracks in the concrete that are caused by the way the cement was made.  Below is the cause of most typical cracking you will find in concrete slabs.

  • One of the main reasons concrete cracks in a new constructed home is water.  Concrete will reach its maximum strength without a lot of water added.  However, much of the concrete used on residential housing has too much water added.  This is done to make the application of the cement easier.  The down fall of this additional water is shrinkage.  As concrete begins to dry and harden it shrinks.  The additional water causes the concrete to shrink more than normal and resulting in cracks.  The added water will also reduce the strength of the concrete once it dry’s.  In some cases, the slab can shrink up to a ½ inch per 100 feet.
  • Other problems than can cause cracks in the slab foundation is improper joint controls.  Concrete like most materials will expand and contract.  Concrete requires joints every so often (the lines you see in sidewalks are expansion joints) depending on the thickness of the slab and the length/width.  If an improper joint is in place the concrete cannot expand properly and will cause cracking.
  • If the concrete is too dry and forms or sets up to fast there is a significant chance that it will crack.  Concrete though it seems simple can be a delicate process of balance in the materials used.

Though most cracks found are normal, there are some that are not.  Having a licensed home inspector look at these cracks to make the correct determination is strongly recommended.

 

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