I just took up a tile floor in my entry hall and discovered large cracks in the cement floor under the mastic I was removing. There are 2 cracks that run parallel to each other across the length of the room. One is a large crack, up to 1" deep in some areas, with a visible cracks under the open area. Evidently the previous owners knew about this, as they had filled it with silicone caulk. However, the floor is level within less than a 16th of an inch, the windows (5) and doorways are level, there are no cracks in the sheet rock or on the exterior of the house in the brick surrounding this area. This entry has a front porch on one side and a covered porch on the other, all bricked. This home was built in 1979 and we bought it 13 years ago. All that being said, is anyone out there that can tell me if I have a structural problem or is it possible that this is a large settlement crack that can just be repaired without additional concern? It looks to us as if the builder poured the concrete on both ends of the house seperately from the entry, which is in the middle of the house but we will never really know.
Can anyone provide some much needed advice?
Can we just fill the voids and lay new tile or do we need to do something else? Oh, one more thing. We live in an area with a high water table and it is a known fact that, in this area,
concrete always cracks. Thanks for any helpful advice.

The pattern of the cracks can be revealing, but it's hard to visualize the pattern from your description. Are you suggesting that the cracks may be where the floors for the sides of the house on either side of the entry were poured? That is certainly a reasonable assumption, if the cracks are located at those points.

Also, it would be good to know how long your entire house is from one end to the other.

Tell your neighbors not to feel so special, that ALL concrete cracks, The trick is to keep the cracks down to microscopic level, so they aren't so obvious.

Your cracks may be where one pour stopped and the other started, or at least one of them may be an expansion crack. If your house is very long, there should have been a control joint somewhere, but these are seldom installed in residential work. Also, if your house has a setback at the entry, creating an inside corner in the concrete, that would be a natural place for a crack to occur, unless the slab is specially reinforced to prevent it. Inside corners are places where stresses from expansion and contraction of the floor are concentrated, thus the cracks.

However, if there is little or no vertical displacement from one side of the cracks to the other, it is unlikely you have a structural problem. The floor may have cracked all it's going to crack, but we won't know that until we know a little more about the exact location and direction of the cracks.

I too have a house with a slab about the same age.
It is not uncommon to find cracks in the floor. Like Richard said it can be several factors that caused this. As long as you do not see any signs of water staining around the edges of the crack, I do not believe you will have any issues.
What I do suggest however if the crack is still pulling apart is that you use a Schulter system under the tile. This will allow some movement of the floor without any cracking of the floor above. Check this out http://www.schluter.com/
for more information

Thank you for your reply. My house is approx. 60 ft. long across the front and 40 ft. deep.
If you picture a rectangle, the entry hall is located squarely in the middle of the box and yes, it is set back about 4 to 5 ft. in the front and the back is inset about 10-12 ft.
The cracks run from the front to the back, on the sides of the floor where the entry meets adjoining rooms. They are not straight cracks
and I am concerned because they are 2-3 inches wide in some areas. What can I use to fill these cracks before I lay down the new tile?
I was planning on installing Schluter Ditra to
prevent future cracking of the tile. There are no water spots visible anywhere. I think these cracks have been here a very long time.
Again, thank you for your advice.
LD

I think both my guesses were right, and that the cracks were caused by a combination of shrinkage (normal) and stress concentration (also normal). I will further guess that the cracks appeared some time during the first year after the house was built, and that they have cracked all they are going to crack.

I should have used the word "shrinkage" in my original reply, instead of "expansion" or "contraction". Shrinkage in concrete is normal, and would be expected in a house of such length. A control joint, which is basically an order given to the concrete to crack "right here" would have controlled at least that part of the reason. A nice typical control joint is a metal tongue-and-groove assembly that is cast into the concrete between separate pours, and allows shrinkage cracks to be at least carefully placed, neat and not random.

By "normal", I mean that the cracks are typical of residential work. They could have been minimized by careful design, using control joints, and some reinforcing bars at 45 degrees at those inside corners, but these are seldom done in residential work. As I said, all concrete cracks, but cracking can be controlled and kept microscopic in size by careful design and construction. Why residential builders or architects don't do it is a mystery, because it costs very little to do so.

As for how to deal with them, I will defer to the hands-on guys like concretemasonry, Home Care Club, Jay In Minnesota, or Maintenance 6, among whom there will be at least a couple who can recommend products to use in filling the cracks. I just draw the pictures. =)

This message has been edited. Last edited by: Richard Hetzel,

I appreciate your advice Richard and Home Care Club. I feel much better now about the foundation. If anyone can advise me as to how to fill the voids in the crack so the floor will be even, please let me know. How do you know if a crack is continuing to open up? What signs do you look for and if you see those signs does it mean you have a structural problem?
Again, this forum is wonderful and I thank you for your help.

I've heard this method described: glue a popsicle stick or tongue depressor to one side of the crack, and mark the other side on it with a pencil...if the pencil mark moves off the other side of the crack, it's still moving. It might take a month or more for any movement to show.

I'm assuming the floor is a concrete slab on ground. If that's the case, and there is no difference in height between one side of the crack and the other, then it isn't a settlement problem or an expansive soil probelm, and those are about the only structural problems that can occur.

As I've said, cracks in a slab the length of yours, with also those inside corners, can be expected, and in fact predicted with some accuracy, unless the builder took measures that are very unusual in residential construction.

I can't help you with repair procedures. I'm hoping concretemasonry or Home Care Club, or any of a few other good people here, will read this and suggest a product to use.

If there large simply use a dash patch cement and trowel it in the cracks.
If they are real small, do not worry about them. They will fill with the cement mastic your going to use to put the new floor down with. If your going to use carpet. You can use a caulk as well.

The only way you will know if the crack is still active is to glue a glass microscope slide over it and see if it cracks the glass after a while. Based on your home type and age, I doubt its really still moving unless your on expansive clay soils and have a water table issue in your area. But even with that, you would see water stains along the edges of the cracked cement,

Thanks for all the help with my issue.
Perhaps you have also help others with all of this valuable information you have both so kindly shared.
Your are both terrific!