a question about the cracks in new house floor

I have a question about cracks on the floor for my new house. The house is at the Central Florida region, which a builder is still building for us. Currently, the foundation, the pipes, the walls and the roof are done with the dry wall installed at the next step. But I noticed there are three very long cracks on the floor around the sink pipe, two of which extend to the boundary of the foundation and are at least 30 feet long. The size of the crack is less than 1/8’’ wide and less than 1/8’’ deep currently since the slab is only one month old. See the attached picture. I was wondering whether the experts here can tell me what you think about the crack. What causes the cracks? Where can I find an engineer to inspect them? Thanks!

There were no “Control Joints” cut or placed in the concrete after it was poured, or when it was poured.

Concrete cracks period, if you do not control which way it cracks, it looks like your picture, perfectly normal

This is some good reading about the nature of concrete.

Concrete is going to crack. If they cut control joints in it the concrete might have minded and cracked where it was instructed to crack.

Control and expansion joints are useful.

Thanks, Dale and Larry. Does it mean that my builder didn’t do a good job here and he should use the cut control joints.

Somebody told me that this type of cracks may be a potential problem since they reached the boundary of the foundation from the center of the kitchen. How do you think?


Don’t worry about slab cracks like these - even if they’ve extended to the perimeter foundation.

The guy responsible for mixing the concrete controls the amount of water in the mix. The distance from the truck to the house and other factors are involved, it’s easier to pour a wet mix sometimes. Then the weather during the curing. It’s rare to see a garage in my area that doesn’t have shrinkage cracks in the floor.

Read the info at Dale’s link.

John Kogel

Cracks in concrete floors is a norm. The floor is poured last and has nothing to do with the stability of a building.

Thanks all of you for sharing your expertise. Can somebody talk about why the cracks are around the kitchen sink pipes and not other places? I forgot to mention that the pipes are for the kitchen island sinks. There are only three cracks and no other crack in the whole house.


look at post 2- 3 again, Dale has already answered that

A lot depends upon the length and width of the floor slab. Let’s say it’s 25 feet wide and 75 feet long, without any control joints. It will tend to crack somewhere near the middle, due to normal shrinkage as the concrete cures, and that pipe sticking up may have created a stress concentration point which would tend to begin the crack. Inside corners are another common stress concentration point.

You know how a crack in a car windshield can begin from a tiny nick caused by a stone? Same idea…the stresses are concentrated by the nick, and the crack begins there and will ultimately probably spread the full dimension of the windshield.

I agree with those who say it is nothing to worry about…probably before the floor finishes are installed, they will patch the crack, and that could be the last you will ever see of it. The concrete floor isn’t structural…it’s just lying on the ground, and it probably has steel mesh in it to help control cracking. Maybe that crack occurred where there was a joint in the mesh that wasn’t lapped or tied, but probably it’s just plain old normal to-be-expected shrinkage.

It is very common to see shrinkage cracks initiated at penetrations through the slab (like that pipe). Those 3 radial cracks are a textbook example of typical shrinkage cracks and are of no concern.

It really is a classic picture and no problem. If you don’t mind I’ll steal it for a powerpoint presentation.