Concrete cracks

JimDRIl

Member
My friend has a new carport floor about two months old. The area is about 20 x 20'. The contractor cut 2 grooves one lengthwise and one crosswise. It now has a couple of long cracks, not open, but very noticeable. Is there something to easily fill these with, or some coating to cover the whole thing?
 
Not likely, must have shrunk and separated, could be several issues to consider, reinforcing, the material itself, the weather when it was placed, hard to say, but once its fractured, even finely, you may be able to seal it with something elastomeric, at the joint of the crack there are sealants/caulking for this, but any coating, with expansion or contracting, the crack is likely to project through, sooner or later. Typically, if none of the above is an issue, relief or control cuts are placed, you don't have this problem on a slab of that size, placed at one time.

There are coatings, but they need to bond and be elastomeric enough to expand and contract with the slab, and most are not, there may be another underlying cause, excess shrinkage, not enough or correct reinforcing, did they place rebar, 6"x6" woven wire mesh, was the material good, what kind of mix design, how about the weather and hydration, (curing) all these can play a role in this.
 
Usually comes down to a well packed proper base.

Rebar will keep the crack from moving up or down or very wide.

Mesh will help a short time, but often gets mushed to the bottom of the concrete so not very effective, and rusts through when exposed on a crack in my winter de-icing climate anyhow.

You can pour some elastic sealer in a crack after it opens up, but not anything for a new crack as you say.

Paul
 
Are the cracks in the sawn joint ot elsewhere?? If in the sawn joint, thats where it was supposed to crack, did this sawn joint open up some? Or, are the cracks else where in the slab. If else where then see what the contractor has to say. It should not have cracked else where if it was sawn within 24 hour of placement. If it was excessively wet, as others have said, shrinkage cracking. Again talk to the contractor. You paid for a proper piece of concrete, you did not get one by the sound of it. gobble
 
IF it is the sawed expansion joint then They make a foam rope that you push about 1/2 inch down into the crack. Then you fill the crack with expansion joint caulk. It will self level and then it will stay semi-soft so it moves with the concrete.
 
Concrete does 2 things "gets hard" and "cracks" All though like others have said, if it cracked in first few days I would talk to the contractor.
 
We use a product here in OZ called Mr Crystal to repair leaks in concrete tanks and troughs

http://crystalfix.com.au/content/how-mr-crystal-works.html

Basically you make a slurry and paint it over the crack and the product wicks in and forms crystals, stopping the leak and protecting the reo. If the tank is moving under load they tell you how to reinforce it with 2 rings of re-bar to stop the movement. One of our tanks has gone from leaking enough to bog a cow beside the tank to minor seeps, which I hope to beat eventually.

Now this is not a slab repair, but a BIL is a professional concreter, and they use a similar product to deal with surface cracks in slabs

http://www.xypex.com.au/

For what it is worth
 

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