Cracks in new slab

[MNMike]

Just had a slab poured last Wednesday and it developed some cracks already. Kind of weird, they are in the corners and it looks like the corner will break off into a triangle. These are not very big, a little larger than a hair line crack.

Contractor says he gets these when he pours on foam board.
The slab is monolithic, vapor barrier, foam, pex tubing, wire mesh. Has 12" x 12" borders with rebar.

Should I be worried???
It's not even a week old.

Thx,
Mike

 

[ForceFed70]

Those look like shrinkage cracks. Normal and nothing to be concerned about.

 

[rburke65]

Curious....how soon after the pour was the floor cut?

 

[DLatham]

NRMCA has articles covering these problems. NRMCA CIP 4 covers cracking and CIP 29 concrete over vapor barriers.
https://www.nrmca.org/aboutconcrete/cips/

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[James-W]

I am certainly not a concrete expert by any stretch of the imagination, but from the picture you posted it doesn't appear to me to be anything serious.

 

[jhawker670]

Just had a slab poured last Wednesday and it developed some cracks already. Kind of weird, they are in the corners and it looks like the corner will break off into a triangle. These are not very big, a little larger than a hair line crack.



Contractor says he gets these when he pours on foam board.

The slab is monolithic, vapor barrier, foam, pex tubing, wire mesh. Has 12" x 12" borders with rebar.



Should I be worried???

It's not even a week old.



Thx,

Mike

I poured my 30x40 slab on 2" foam board 1 month ago and i dont have those cracks. But i have seen them before. I dont think its a biggie unless they open up


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[MNMike]

Thanks Guys,

He cut the lines the next day, the slab was kind of pricey so I was freaking out.

I won't worry about them. They will be covered with epoxy sooner or later.

 

[lakeroadster]

Excellent Reference Article For Evaluating Concrete Problems

Some Research: Visual Inspection of Concrete

 

[LegacyIndustrial]

What is the saying....
Some concrete will crack and the rest will too!!

 

[Shootinok]

my concrete guy gave me a fire and theft guarantee...
and assured me it would crack.

 

[n20junkie]

Thanks Guys,

He cut the lines the next day, the slab was kind of pricey so I was freaking out.

I won't worry about them. They will be covered with epoxy sooner or later.

He should have cut them before leaving the site on pour day.

 

[ForceFed70]

He should have cut them before leaving the site on pour day.

That's expecting a lot. Pour day often runs late into the afternoon, and you need it to harden before cutting.

Cutting next day is most common.

 

[73RR]

There are many contributing factors to cracks; not cutting soon enough (as soon as you can walk on it), not cutting deep enough, too much mix water (high water/cement ratio), inadequate sub-base prep and too thin of section vs panel size.
The concern is the crack 'gap' and location with regards to what is going on top of it/them.

 

[atthebeach]

I recently had a slab poured for my 15' x 20' shop addition which began cracking while the slab was still being finished. Two large cracks perpendicular to each other. This same contractor has done similar slabs for me in years past of the same general design which have yet to crack. This time it was an unusually humid day with temperatures in the 80s. He went on to remove the forms and cut the relief lines the same morning the concrete was poured.

The foundation design in the middle of the slab called for the standard 4" of gravel covered by a plastic membrane and wire screen. My contractor said plastic in direct contact with concrete can cause concrete to setup too fast on warm humid days. He said putting an additional layer of gravel between the plastic membrane and the concrete will avoid this type of cracking. Next time I'll change my design to include an extra layer of gravel.

 

[lakeroadster]

Thanks Guys,

He cut the lines the next day, the slab was kind of pricey so I was freaking out.

I won't worry about them. They will be covered with epoxy sooner or later.

He should have cut them before leaving the site on pour day.

That's expecting a lot. Pour day often runs late into the afternoon, and you need it to harden before cutting.

Cutting next day is most common.

https://www.concretenetwork.com/concrete/slabs/controljoints.htm

"In hot weather, concrete might crack if joints are not cut within 6-12 hours after finishing concrete. In this condition, if you don't want to use a grooving tool to cut joints, there are early-entry dry-cut lightweight saws that can be used almost immediately after finishing. These saws cut 1" to 3" deep, depending on the model."

 

[ForceFed70]

https://www.concretenetwork.com/concrete/slabs/controljoints.htm

"In hot weather, concrete might crack if joints are not cut within 6-12 hours after finishing concrete. In this condition, if you don't want to use a grooving tool to cut joints, there are early-entry dry-cut lightweight saws that can be used almost immediately after finishing. These saws cut 1" to 3" deep, depending on the model."

Should, should, should - I'm just sharing what I've actually seen. Most pour days go into mid/late afternoon with slab finishing being the last step. You really think contractors are coming back at midnight to saw-cut? OP says it was poured early June in MN - doubt it was that hot anyway.

I'd like to know more about this saw that can cut a control joint in cement that's just been finished. It's got to be darn soft to finish.

Poll the board 90%+ will say theirs was saw cut the next day.

 

[lakeroadster]

I'd like to know more about this saw that can cut a control joint in cement that's just been finished. It's got to be darn soft to finish.

http://www.mkdiamond.com/concrete/saw_srx-150.html

https://search.yahoo.com/yhs/search...e+saws+&ei=UTF-8&hspart=mozilla&hsimp=yhs-001

 

[bigman68]

The original:

https://www.husqvarnacp.com/us/machines/soff-cut-saws/

 

[Mr. D]

I had a concrete tell me if you don't like cracked concrete don't use concrete.