New Monolithic Slab Has Crack - Your Opinion

[ldovekk]

I had a 30' X 40" monlithic concrete slab poured for my new shop. I had the contractor put a drain on each in the middle on each side. They brought in 90 yards of fill to level the foundation. I was out of town when site was prepped & the concrete poured so I wasn't able to see everthing being done but I was abe to inspect the work 2 days after it done.

My problem is there is a very small crack that runs from the edge across the middle of the slab to one drain inlet and the to the other drain. This crack was there from the 2nd day after the concrete was poured. As this area will occasionallly be exposed to water I anticipate over time this will be a problem?

What should I expect and/or require (if anythhing) the concrete contractor to do about the crack. What would be the best way to repair the problem?

Your input is appreciated.

 

[Fastback]

Was the floor properly cut after it was poured? How many cuts etc..? Floors can crack, mono pours with drains and slopes to those drains could really crack if the floor gets thinner near that drain due to fall & pitch changes.

 

[pop pop]

Unfortunately it can't be repaired. There are things you can do to try to mask it. But short of repouring it, the crack will always be there.

Concrete will show a shrinkage crack every 15 to 20 feet. It can't be avoided, but can be contained and controlled with the mixture and additives and reinforcements.

Guys I use to work with say there is two kinds of concrete. That that has already cracked, and that that will crack.

 

[Toomanytools?]

Two things I can guarantee with concrete. 1. It will get hard and 2. It will crack. Prep is important, compaction of the gravel is very important.
Since you weren't there hopefully the concrete contractor did what was needed. It is a little late now to worry about that though. You could have them saw kerf the crack trying to keep it as straight as possible and follow the crack. Then fill it with a concete caulk.

 

[Al Bundy]

Was the site properly compacted after it was filled? How thick is the slab? Was there any wire or rebar used in the slab? Are there any control joints? The answers to these questions determine why your floor is cracked. Yes concrete will crack, that's why they put control joints in it. If it cracks somewhere else, it's either substandard workmanship or a catastrophic event like an earthquake.

 

[Falcon67]

I have several in my slab about that same size. No big deal and once they formed, they didn't grow. They are all totally random in nature. I chose not to put in control joints. My slab was poured on days where sun exposed concrete surfaces would be arouund 130F in the daytime, so shrinkage cracks were pretty much expected. Kinda odd that it traveled to the drain hole. I'd think the drain pipe would be below the concrete so as not to create a weak area.

 

[Kevin54]

I'd get some control joint cut in for one thing that may radiate out from the drain. This will help stop water running where you don't want it to and any cracks from the frain will find the control joint. As far as the crack you have, about the only thing you can do is get a diamond wheel, gouge it out, and get a can of some of the flooring material from the flooring people and fill it. Or if it's just going to be a working garage and not the Taj Mahal, gring it out and fill it with some Rage filler (bondo) sand and level

 

[Wardster]

If the concrete is reinforced, then the crack may never get any bigger and might not be a problem. Shrinkage cracks like the one in your picture can be 'fixed' with a good penetrating sealer. If the crack is not sealed and is exposed to freeze/thaw, then it will most likely get worse over time.

 

[Provincial]

My bet is that the contractor added the drain pipe without putting it below grade, so the pipe is embedded in the concrete. That left a thin cross-section which cracked. If so, it may be a good idea to add a saw cut to continue the line of the crack from the other side of the drain.

I agree with toomanytools and kevin, saw cut along the crack and caulk it to make it look intentional.

 

[Mr.Magoo]

The crack is typical of a shrinkage situation at the surface, also, maybe because the pipe is directly below the concrete, maybe closer than it should be. This crack is appearing as always when a pipe, drain, conduit post or other protrudes through the surface, just happens to be a starting point as it shrinks. Like others have stated, cut some reliefs into the surface to avoid any more maverick cracks, the stress will be relieved and follow the control cuts you make, make 10' x 12' cuts or whatever comes out even for the size you poured. I say like others, I can guarantee concrete will crack, especially if you look at it wrong. Today without much surface troweling, it is more prone to surface cracks, we used to throw powdered steel on the surface and a lot of power and hand troweling, today, they rod it, tamp it, put the bullfloat and Fresno to it, touch it with a broom and leave. The world has changed. Anything you can do to mask it will help.

 

[rasit]

This crack is appearing as always when a pipe, drain, conduit post or other protrudes through the surface, just happens to be a starting point as it shrinks.

+1 for shrinkage and weak spot. Look a little closer at the pic and notice another crack @ upper right...

 

[Gary S]

Unfortunately it can't be repaired. There are things you can do to try to mask it. But short of repouring it, the crack will always be there.

Concrete will show a shrinkage crack every 15 to 20 feet. It can't be avoided, but can be contained and controlled with the mixture and additives and reinforcements.

Guys I use to work with say there is two kinds of concrete. That that has already cracked, and that that will crack.

Agreed 100%. Concrete can't be repaired.

On any slab of concrete over 15-20 ft, you need to make control cuts. They don't prevent cracking, they control the crack into nice straight lines. That's the reason they are used by most contractors.