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We purchased the house about 2 years ago. The house is about 50 years old. Today we removed the carpet and the hardwood floors under the carpet. We found out the slab has an approximately 10ft long crack. See the picture. The crack goes from hairline and branches off to bigger cracks. See photo. It's about 5 inches deep from what I could measure.

The house is in Granada Hills, California. I was thinking it's maybe due to earthquakes or earth shifting. I know a major earthquake happened in 1994. The walls appears to be fine and show no sign of structural damage.

What type of crack is this? How can I fix it and should I be concerned? Should I use cement, Emecole 555 or a bottle of concrete filler? Any help or insight would be appreciated.

enter image description here

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This crack looks concerning to me. I'm not one to pay money for people to do work on my house, but I'd bring out a foundation expert on this one if no one can provide an acceptable response. If no foundation issue is present, just chisel out a upside down 'V' and fill with small aggregate concrete. –  Edwin Apr 9 '13 at 8:39
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is the floor still flat or has there been any displacement? Can you see any rebar embedded in the floor? –  shirlock homes Apr 9 '13 at 9:54
    
@shirlock I cannot see any rebar. The floor looks flat, maybe slight buldge where i chiseled out this piece. But it's hard to tell. I pointed a thin metal rod in the crack and i measured about 5inch deep. What's under this concrete slab. –  Hussein Apr 9 '13 at 15:53
    
What brought it to your attention? –  mike Aug 25 '13 at 6:25
    
The slab looks very thin. Settling crack I suspect. Not even thick enough for rebar. That's the issue. –  Matt Sep 24 '13 at 2:18
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2 Answers 2

This is not going to be the answer you wanted to hear, but here goes.

Although I cannot see the cracks up close, it appears that the cracks were created by the floor flexing in a fairly straight line. The cracks wander in a band about a foot wide with some parallel and joining cracks.

My first plan of attack would be to remove a rectangle of the damaged and weakened concrete apx one foot wide by the length of the crack, apx 10 feet. This can be done with a small hand held jackhammer. ($30 to $40/day at rental store). Slightly bevel the edges back from the surface to create an inverted "V", so it is slightly wider at the bottom than the top. Once the edges are clean of dust and chips, carefully fill the open void with a mixture of concrete mix equivalent to a 5000 pound mix. You can use a ready mixed in a bag, just add water. Keep the mixture a bit to the stiff side, not too wet. Fill the entire void be sure to push the mix tightly against the existing concrete. Wetting the existing concrete isn't a bad idea. Trowel smooth. Done.

The reason I would not recommend a quick fill fix is that there may be lots of other cracks below the surface. If you don't get a good solid patch, water could wick up through cracks or the hidden damage could compress or further separate in future shakes. Although it seems like a big job, a 1 foot by 10 foot removal and repair is not as bad as it sounds. With the proper tools, you should be able to do the whole job in 4 to 6 hours. Good Luck

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Don't worry about it. Just put some crack filler and put your new floor over it. Every house has cracks like that. It's on the slab, not the foundation.

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