Should I cut control joints after a month and a half?

[fordluver4x4]

Hi, I’m fairly new here but have been lurking and reading a lot for a while. I was finally able to have a 32x30 detached garage/work shop built (in southern PA). The floor slab was pored about a month and a half ago. It was not cut and currently has no visible cracks. The contractor is willing to come back and cut control joints in it, but I’m wondering if at this point I should leave it uncut? I read that “Cutting freshly poured concrete too late can lead to unwanted cracks in the concrete, rendering the joints ineffective.” My preference would be a smooth uncut slab, but I also don’t want to end up with random jagged cracks. Also if he does cut it, the correct spacing would be +-10’ squares correct? The slab is 32x30, supposed to be 4” thick but I didn’t actually check, if anything I think it may have ended up a little thicker. It has rebar in it. I should also note: at 2 places the slab is about 12” at the edge, dug down beside the footer where the block knee wall didn’t toatlly sit on the footer... long story for another time. Oh and one final note: there is a dark, almost damp looking, line running across the middle of the floor, almost looks like that area isn’t totally cured yet? Maybe where rebar is to close to the surface? Not really noticeable but thought maybe worth a mention.

Also, the front apron (+-32x20) was pored about a week ago, it is also not cut or cracked. The contractor does not suggest cutting it. It has quite a few angles in it due to slope and I’m not sure you could really cut squares in it, may have to follow the contour which may look weird. Thoughts on cutting the apron as well?

Thanks for any advice.

 

[ConCretin]

Concrete shrinks as it sets inducing tension in the slab. Control joints are designed to relieve this tension by inducing a crack at the bottom of the cut where you won’t see it before a random crack occurs where you can. Most of the shrinkage occurs early, which is why saw cuts should be made immediately after finishing.

Your slab is fully cured by this point and there is a pretty good chance that if you haven’t got any cracks, you won’t get any. It’s not all that unusual for a slab of your size to avoid shrinkage cracks. If you were to cut some joints, one in each direction would be fine.

 

[Jakemedic]

Hello! My contractor came back yesterday at about the 24 hour mark to cut the relief cuts. Looks very good as well. Best of luck with your project!!

 

[Retroman]

I would cut the apron coming off of any outside corners if there are any that is where they will typically crack out of.

 

[PhantomEB]

I did just that about the same time after my garage was locked up. My brother and his 28x32 is kicking himself for not doing it. I would do it to any shop I can around any cracks even 10 years after the fact.

 

[fordluver4x4]

Your slab is fully cured by this point and there is a pretty good chance that if you haven’t got any cracks, you won’t get any. It’s not all that unusual for a slab of your size to avoid shrinkage cracks. If you were to cut some joints, one in each direction would be fine.

Thanks for all the replies. I think I’m going to go with what LLWillysfan said and hope that if it hasn’t cracked yet maybe it won’t. I’d rather not have any cuts in it, so if I’m past the most likely time for cracks I think I’ll just take my chances.

Thanks again to all who replied.