Expert: Bruce E. Johnson - 5/5/2010

Question
I live in Minnesota so the ground freezes. The soild is very sandy.  My garage floor and apron are one piece.  There is a cut about 1/2 in deep between them. I have a crack in the garage floor about 2 1/2 feet from the apron, that runs width wise the whole way across the garage. I was told the crack could be caused by the apron heaving and I should take the cut all the way through to seperate the apron from the floor. If I do it, I would not be able to go the whole way across as the blade would hit the wall. What are your thoughts about making this cut?

Thank you I really appreaciate your time and help.

Answer
Hi Steve, my guess is that your garage/apron slab has a monolithic footing incorporated into it to support the front of the garage and it is the backside of the footing that is showing up in your crack, especially if the crack is in a fairly straight line. Doing a saw cut will encourage the crack to stay straight and may dress it up a bit, it can even be filled with an expansion sealant like Urethane self-leveling caulking.  As far as getting the saw cut all the way to the wall, in these instances we use a 4-4 1/2" grinder with a concrete blade in it to finish out sawcuts like this. You don't need to saw cut too deep, 1" in depth is generally sufficient.  Saw cutting concrete is used to encourage cracking to take place in a specific location and is called a "control joint".  Apparently the control joint cut across your apron didn't work and the concrete cracked where it wanted to on the backside of the footing instead of the front side.  This happens. Concrete has a mind of its own sometime even when we take precautions.  I never pour garage slabs and aprons together for this reason.  I usually pour the apron separately with an expansion joint between the two.  But that doesn't help you at this point in time.  Do your saw cut and fill it with a flexible sealant.  I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com