Thread: Concrete slab crack in living room

We purchased the house about 2 years ago. The house is about 50 years old. Today we removed the carpet and under the carpet the hardwood floors. We found out the slab has about 10ft long crack. See picture. The crack seems to branch into separate cracks. It's about 5 inches deep from what i could measure.

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

Do i need to fill the crack at this point or leave it as is. Should i be concerned. If it's a DIY job, Should i use cement, Emecole 555 or bottle of concrete filler. The crack goes from hairline and branches off to bigger cracks. See photo. Any help or insight would be appreciated.

2013-04-08 16.17.47.jpg

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Yep, that is a crack and it loos like a pretty good one. Has the house moved? Any problem with doors and windows not working properly? Any wall cracks?

If the slab has failed which it kind of looks like in the picture you really should gets good foundation contractor involved.

Black floor glue - good chance it has asbestos in it. Don't grind or sand the glue.

Did the flooring have gaps in it before you lifted it? It could very well be old damage from an earthquake. I will echo Scott, get a pro to take a look.

You may want to have a structural engineer look at it. That's a pretty good crack, and if I saw it during an inspection, I would advise further investigation by a civil/structural engineer


Matt Fletcher
Joe Viglica, Professional Engineer

I am curious whether or not any put a level on each side of the crack to see if each side was still 'in plane' with the other side - are both sides level, do both sides slope the same direction, do both side slope up toward the crack, do both sides slope downward toward the crack, does one side slope upward toward the crack and the other side slope downward toward the crack, etc.

I'm guessing that both sides slope upward toward the crack.

Granada Hills is right near Northridge and Sylmar, isn't it? Could be earthquake from the 90s or the 70s. If on a hill, could be soil movement. If on the flat (or hill, for that matter) could be expansive soils.

Looks like dirt/soil where that chunk of concrete was removed. Is it?

Is the slab 4" thick? Doesn't look like it to me.

I also don't see any welded wire mesh. Not that WWM would prevent cracking, but it is typically a part of a concrete pour.

As has been said, I would suggest an engineer review this.

This is just a wild guess, but kinda looks lake a crack that is sometimes caused by a root.

As someone else said, put a level of straight edge across the crack to see if the floor is level. Its a large crack. If the slab settled or heaved it would probably be noticeable. The slab may have shifted laterally (especially if the house is on a hill). Earthquake is a possibility. You could patch the crack with cement as a way to monitor it for further movement. You could use a structural epoxy to patch it, but if something is causing movement the epoxy probably will not help and if no further movement occurs then it does not matter too much what you patch it with. Consulting a structural engineer would be a good idea, but if you do not want to spend the money that monitoring is a good approach. Of course, if you cover it with flooring that is not easily removed then monitoring is not practical.

There have been at least three major earthquakes since this house was built, all in the general area of Granada Hills. I lived in San Fernando during the 71 earthquake.I think you would be hard pressed to find a house of that era that did not have signs of movement.

That said, you may want to have an engineer look at it if there are signs of problems such as doors racked, etc. However, lots of damaged homes were looked at after the earthquakes by engineers to make sure they were OK. You might be able to find past documentation at the Building Dept, but could be difficult considering the amount of time that's passed.