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Question DetailsAsked on 12/1/2013

why are there cracks in basement concrete floor

I'm trying to find out if the cracks in my concrete basement floor are normal. I recently found out that I have a busted drain pipe under the concrete since the house has been built 8 yrs ago. I'm concerned whether these cracks are a result of the pipe being busted or something else.

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5 Answers


You say you "have" a broken pipe under the floor. If the pipe was never fixed it is possible that the broken pipe is causing the problem by eroding the soil under the slab by a siphon action of the soil near the pipe. You did not say if the cracks were near the location of the pipes though. Many slabs do crack as the soil settles. On residential jobs many contractors will take a short cut and not compact any fill added to level the floor prior to pouring concrete. On larger commercial jobs usually there is either an engineer or job super watching over each stage of construction. You can still get some small contraction (shrinkage) cracks on larger floors though even with good soil beneath. You say the house is only 8 years old so it may be possible it is covered under a HOW program. I am not sure of which states require this but in mine it is. Since I have scaled back to mostly renovation work I am a bit rust on what it covers but I think it was for a 10 year period and covered this sort of thing. If the cracks are not i the area of the pipe and are small with no elevation differential between the sides of the cracks it may very well be just shrinkage cracks and are not anything to worry about.


Answered 6 years ago by ContractorDon


I agree with Dan. One way of checking movement of concrete is to tape the crack, If tape cracks or comes off, crack may be active and further action may be necessary. You can use sand or polyurathane rope caulk to partially fill the crack, then use a good sealant like Geocell in grey to fill last 1/2 inch or so. ( All available at Menards.) If you do not use a filler you can caulk to China, so do your self a favor and always use that technique inside or outside on concrete. Old contractors joke "what guarantee do you get with Concrete?" That it will crack.

Jim Casper Very old Water Control Guy

ps for tips on gutter and covers see my blogs


Answered 6 years ago by jccasper


I don't know how to reply to your comments on here but.....

The pipe has not been repaired as of yet...working on it. The cracks have been there since the house has been built but they are expanding. There are two main cracks that I'm concerned about. Both are going in opposite directions with hair line cracks now.

Answered 6 years ago by Tish


As I said before if they are near the pipe problem that could be the cause. As the homeowner you may not have the tools to know exactly where the pipe runs. If you look at the base of a leader pipe from your roof you can see what happens when water is running over soil. If the break in the pipe is just right it can suck the surrounding soil with the water from the leak. You see stories about this condition about sink holes created in city streets from broken water mains all the time in the news. A drain pipe can do the same thing but at a slower rate. If the cracks are making an X and the floor seems to be sloping to the cracks it is settling either from the leak or poor compaction when the house was built. If the floor is staying flat it is shrinkage. I would need to see it to give you a better answer. There is a reason they put expansion joints in concrete.


Answered 6 years ago by ContractorDon


When the pipes are repaired, make sure they check for voids under the slab. If there are any, they should be at least concreted to eliminate them. A more professional but also more expensive way is to mudjack them - pump in grout under low pressure to fill all voids.

Unless these cracks are vertically offset or more than about 1/8" wide, I would wash out (or use compressed air) and a sharp pointed pic to clean the cracks after the pipe is fixed, then fill the joints with a creamy mix of portland cement or concrete fixit type grout (preferred), or you can get concrete caulk that comes in tubes for a caulk gun and caulk the cracks, smoothing it with a wet putty knife. Then watch their growth over time - if just a gradual hairline crack that does not vertically offset across the crack or grow more than an eighth inch wider over a decade or so, then I would not worry and would just close it back up with grout or caulk periodically. Obviously, while this is growing, putting any type of tile or stone floor on top of it would not be a good idea, as the crack will propogate through them too. A floating floor should be no problem, but of course you loe the ability to see how much the crack is growing.

If you can describe how the cracks run relative to walls, doors, etc it might help to understnd what type of cracks they are, especially since you said they have been there since the house was built. Also, are there matching cracks in the foundation walls ?

Answered 6 years ago by LCD

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