How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
Why are there score line grooves in the concrete floor of the garage?
Monday, August 6, 2018
They are called “control joints” or “contraction joints.” Concrete shrinks a little as it cures and hairline shrinkage cracks are unavoidable, especially in large slabs. While the cracks are unsightly, they do not affect the structural integrity of the slab.
But it can look scary to a homeowner, so contractors cut a score line across large concrete slabs, like in a two-car garage or large driveway apron, running in both directions. It’s usually done with a concrete saw shortly after the concrete is placed and finished, and the typical depth is three-quarters to one inch—just enough to weaken the slab slightly at the score so that any cracks happen at the bottom of the score line, where they are not noticeable.
The photo below was taken at the outside wall of a garage, just below the siding. You can see the bottom of the scored notch at the side of the slab and where the hairline shrinkage crack opened below it. Cutting contraction joints in concrete does not guarantee that a meandering crack will not appear, but it reduces the likelihood of it.
Also see our blog post What is the difference between a carport and a garage?
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