basement level foundation slab issue

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Posted by: from Toronto
8/10/2011 at 2:00:00 PM

We have a 3 level side-split built in the mid-60's in Hamilton, Ontario. The basement level floor (in the family room) has cracked and is heaving (approximately 4-6 inches from rest of floor). No separation at crack has happened - floor is still generally smooth but with a definite up-slope. No apparent damage to inside or outside walls is visible. The main crack is approximately 6-8 feet from the foundation wall (minor secondary cracks have also occurred because of this). We have experienced no leakage or other damage. There is no reason for pipes to be in the vicinity of this area as all kitchens/bathrooms are in or near the front of the house or on the other side of the basement. The furnace is also on the other side of the basement. There are no large trees on our property or within 30 feet of this area. Looking for ideas as to cause and also who or what specifically to look for in a contractor so we can get it fixed.

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Date/Time8/15/2011 at 12:48:14 PM

Hi Dean, It actually sounds like you have a well installed concrete floor. If it has heaved 4 - 6" without major separation at the crack, the wire grid in the concrete is doing it's job well. The bad news is that you are going to have to break up the floor along and around the crack to find the cause and deal with it. I wouldn't rule out tree roots as they actively search for water and grow where they find it. They can extend 30 to 40 ft. outside the canopy of the tree. This is just speculation but it sounds like you had a void under the concrete that collected some water and the roots found it and liked it! You aren't seeing any water damage because the roots are sucking it up. The first step is to break up the concrete - anyone from a foundation contractor to a handyman can do that for you. Once you discover the problem, you can post the project here to get estimates, quotes, or suggestions. Good luck with it!

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Date/Time8/17/2011 at 12:54:15 PM

Jim is correct in that you will have to break up the concrete to have a look. There are a number of reasons for this to occur. We renovate a lot of basements and when breaking the floor we often find broken or clogged clay weeping tiles that run under a basement floor and/or clay soils that have created hydrostacic pressure to heaving.


Kingsway Construction Inc

Glenn Rosborough

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Dean in Toronto
Date/Time8/23/2011 at 10:49:30 AM

Jim / Glenn,

Thanks for the responses!

We had someone in yesterday to break up the floor and found the issue right away. The concrete in the area that heaved was only a couple of inches thick. The gentlemen doing the work (Warren & Shawn) excavated an area approximately 20 sq ft in total and noticed the further out they went the thicker the floor got. They tied into the existing slab the best they could and poured us a beautiful new, flat floor.

I was afraid of tree roots or water build-up, but never expected to see shoddy workmanship!

I guess the saying "They don't make 'em like they used to" doesn't apply here.


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