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sluggermike 10-17-2007 03:43 AM

Concrete slab cracking Concrete slab cracking
About ten years ago I built a 14' X 24' family room extension on my house. I did everything except for the concrete slab which was a mistake. The person I contracted with to do the cement work mentioned to the guy who was pumping the cement that ithe cement seemed too wet. I didn't know any difference, and the cement contractor who should have told him to get another batch let them pour it anyway. It looked good for awhile and then it started to crack. The footing around the perimeter seems OK, but the interior has a lot of cracks, some 1/4" wide. Is there anything I can do to fill the cracks and prevent it from cracking further?
I want to put down a laminated wood flooring, but I'm concerned about the condition of the cement.

joasis 10-17-2007 04:36 PM

Was there no steel laid down? 1/4 inch wide cracks, especially if you can tell they are still opening up represents a serious problem. Concrete achieves most of it's strength at 28 days or so, and the "wet" mud probably detracted from the strength.....did you compact the sub base before pouring?

concretemasonry 10-17-2007 04:55 PM

Flooring > Concrete slab cracking
10 year old concrete?

At that age, it is done shrinking. If you have no wire to hold it together, it can settle if the base is not stable. If not the cracks can just increase or decrease depending on the conditions.

If it is stable, you could caulk the joints, but that would not do much.

If you want to install a laminated wood floor, you will have to prepare the surface for that flooring material. If you do not have a vapor barrier, the preparation efforts could be substantial. - A good flooring supplier or contractor can tell you about the preparation.

sluggermike 10-17-2007 09:58 PM

There is steel in the slab. I don't remember them compacting the ground prior to pouring. Some of the slab was poured over an existing concrete patio. It's interesting that there is a crack running around the perimeter about 12" in from the edge of the slab which is probably the width of the footing. I've seen some cement crack filler at HD that comes in a tube. Would that work, or do you think it might just continue cracking?

JazMan 10-17-2007 11:35 PM

A crack filler will do just what it says. There is no force on earth that can keep the slab from moving. Is the floor level? Are both side of the crack flush, or is one side a bit higher? Since you're going with a floating floor you might be able to get away with it, with the proper laminate underlayments?


sluggermike 10-18-2007 12:08 AM

The slab is level even where there are cracks. I just checked it with a straight edge.

joasis 10-18-2007 12:11 PM

I missed the original point of 10 years. You have a shifting problem, and a nothing, short of mud jacking will stop it. I generally will refuse to pour concrete over existing concrete for any reason...the exceptions being if the existing slab is good, and there will be no load on the new floor...we also drill through the existing slab....much easier to break it up and remove it. The crack appearing around the perimeter is a great indication that the sub base wasn't properly compacted.

sluggermike 10-18-2007 12:28 PM

What is mud jacking? What do you suggest that I do? Will the slab hold together since the footing seems to be OK, and I know that there is steel in the slab. Thanks

sluggermike 10-18-2007 12:30 PM

I watch Holmes on Homes, and I know he would probably re-pour the slab, but I don't have the money to do it.

joasis 10-18-2007 08:45 PM

If you are tight on money, we don't need to talk about mud jacking......but for the curious, it is pumping concrete under pressure to the underside of a slab to stabilize it, or raise it, etc. I have only seen it done once, and it was impressive.

sluggermike 10-18-2007 11:21 PM

I Googled it and found out that mud jacking is not recommended for house slabs. According to the source I read it is hard to control where the "mud" goes, and it can put too much pressure on in ground plumbing causes it to the pipes to break.
Do you have any suggestions short of pouring a new slab as to what I should do. I'm tending towards just getting a cement crack filler. I really appreciate the information you have given me.

JazMan 10-19-2007 12:06 AM


Explain what crack filler is going to do for you? You are not going to see the cracks once covered. Now if you were painting the floor, that might make a difference?

You need to evaluate if the floor is flat enough for the laminate you plan to install. If it isn't, then you either rob Peter to pay Paul, or just go with carpet.:no:


sluggermike 10-19-2007 02:40 AM

I get your point about the crack filler, but I think I'm going to do it anyway. It will make me fill better knowing that the cracks under the laminated floor are filled. It was my hope that it would stop the cracking, but I know that's not the case. BTW the floor is flat and level.

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