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I have a 25-year old concrete floor. It was poured (4″) inches thick with wire reinforcement over approximately 4″ of gravel. A shallow footer approximately 18″ deep was dug and poured. A row of concrete blocks laid on top of the footer and used to form the concrete floor. A couple of years after being poured a hairline crack appeared down the middle of the floor in the approximate location where the screed board was pulled out. This last summer, which was very dry, the crack widened and is now 1/2″ to 3/4″ of an inch wide. The floor has shifted and my garage door no longer closes easily. Is there any way to repair this, short of pouring a new floor? Why did this happen? Shrinking and swelling of the clay underneath? Or, should I just leave it alone. Could I just scribe the garage door to fit the new contours of the shifted floor? Or do you think it will continue to shift? How would I go about pouring a new floor? Sounds like major construction to me. Comments please. Thanks.
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Sounds like differential settlement to me. During last summer when it was very dry the ground under the edges of your slab has dried out and settled or shrunk relative to the centre of the slab. This is what opened up the crack.
You can repair by drilling holes in the slab and injecting a cement or chemical grout to bring the floor back to level. This is a fairly common repair method though it may not close the crack right up. Unless the floor no longer drains, I wouldn't bother with grouting. I'd just modify the door so that it closes and seal the crack to keep dirt and water out. If the crack lets a lot of water get into the ground under the slab you are going to have all sorts of fun with your slab's levels.
*Thanks, that's not too far from the opinion I came up with. I hadn't thought about that kind of a repair though. I was thinking more like cutting around the walls with a concrete saw, jackhammering the concrete and re-pouring. You idea sounds easier. Thanks.
*With a slab, unless the problem has significant structural ramifications, I always look for the easy fix first. The breaking out part of the slab and re pouring sounds much too like hard work to me. And you risk doing big damage to the wire reinforcing.Provided your foundation is not moving around and no trees are growing roots under the slab you should be alright. Keeping dirt and grit out of the crack, and preventing water from entering the crack and saturating your foundation would be my priorities. I'd just scribe the door so that it closed easily.
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I have a 25-year old concrete floor. It was poured (4") inches thick with wire reinforcement over approximately 4" of gravel. A shallow footer approximately 18" deep was dug and poured. A row of concrete blocks laid on top of the footer and used to form the concrete floor. A couple of years after being poured a hairline crack appeared down the middle of the floor in the approximate location where the screed board was pulled out. This last summer, which was very dry, the crack widened and is now 1/2" to 3/4" of an inch wide. The floor has shifted and my garage door no longer closes easily. Is there any way to repair this, short of pouring a new floor? Why did this happen? Shrinking and swelling of the clay underneath? Or, should I just leave it alone. Could I just scribe the garage door to fit the new contours of the shifted floor? Or do you think it will continue to shift? How would I go about pouring a new floor? Sounds like major construction to me. Comments please. Thanks.