New home with 2" thick concrete slab in basement

by Jason D
(Woodbridge Ontario )

Q. Ive been living in my new home a little over a year now and have noticed the cracks in the basement floor worsen. Some cracks are almost 1/8 thick and about 1/16 offset. The floor vibrates when I stomp my feet in many of the cracked areas. Frustrated I drilled in various areas to discover only 2" of concrete thickness even as little as 1 1/2 inches. What problems will this cause and is 3" code for slab thickness?

A. I'm not sure what code is in your area. We always pour at least 4" of concrete for basement floors.

It sounds like the sub-base wasn't properly compacted, hence the vibration when you stomp on the concrete. The problem with the concrete floor being so thin is it will not be able to support much weight without breaking up and getting worse.

The cracked, thin concrete should be removed, the sub-base properly compacted (hopefully you have gravel under there) and a new 4" thick concrete floor poured.

Install concrete expansion joint material around the perimeter before pouring and saw concrete contraction joints in the floor the same day (hire someone who has a soff-cut saw).

Spray or roll on a concrete sealer after sawing.

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