How to fix gap under basement slab


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Old 10-08-15, 02:30 PM
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How to fix gap under basement slab

Hi,
I pulled up some pavers behind my basement door today to level out a dip that was causing water to pool near my wall. When I cleared the pavers it exposed a gap under the basement slab, which looks like it extends a few inches under and beneath the slab. I'm guessing this should be filled in to avoid cracking/settling in the future. Is this a job that would best be done by filling in with concrete, or would filling with gravel do the trick acceptably? I was planning on just leveling out the pavers with some sand but it seems like that would just get washed into the gap and not help in the long run. I don't know squat about foundation or concrete issues, so any input would be appreciated.

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Old 10-08-15, 03:52 PM
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foam-in-a-can ? it will fill the area & prevent water intrusion to a large extent
 
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Old 10-08-15, 06:00 PM
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I thought about that as a way to keep sand and water from flowing under there, but I thought maybe the gap should be filled with something solid. That would certainly be the cheap fix.
 
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Old 10-11-15, 10:34 AM
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Be very careful when using expanding foam under concrete. One of the DOT building maintenance guys at my former employer used foam under a concrete slab at several doorways, and it raised and cracked the concrete. Funny that a $7 can of product can cause thousands of $$$ of damage (they had to bring in a concrete repair outfit to remove and replace the damaged concrete).
 
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Old 10-11-15, 10:58 AM
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normally bdge & i agree altho it seems at times we take different paths to arrive at a common opinion,,, the apron/vest brand of foam-in-a-can has no structural property as its mostly insulation,,, polyurethane foam injection is as strong as cementitious mud/slabjacking however foam expansion continues after the material being pumped is cut off,,, the operator has to be VERY considerate of the amount of activator melded into the poly OR what bdge describes rapidly & OFTEN occurs
 
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Old 10-11-15, 12:57 PM
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Also they have both expanding and non expanding foam. Door and window companies recommend only the non expanding so I assume, though I haven't tried it, if it won't distort a jamb it won't break concrete.
 
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Old 10-16-15, 07:11 PM
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I appreciate the input, and went with the version that is for sealing up to 1", since that was about the height of the gap. I did a couple of sweeps to fill in behind the visible gap, hopefully it does the trick.
 
 

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