Foundation stress crack repair idea


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Old 02-07-12, 03:59 PM
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Foundation stress crack repair idea

My house's foundation/retaining wall runs the property length but the house only sits on half the wall, so a foundation wall runs perpendicular from the center of the retaining wall, which holds up the a wall of my house. I discovered some cracks and a sort of trench in the dirt at one of the corners. I talked to a contractor today who recommended that I run rebar through the cracked foundation and tie it back to the retaining wall on both sides, then pour concrete over the whole thing to brace the weak part. He said the trench in the dirt just means water has been collecting there, but he didn't see any sign that my foundation was undermined.

I'm not a masonry/concrete guy and know nothing about foundations, so I was wondering if the plan raises any red flags for someone with more experience than I.

IMG_3016
In the picture the rebar would be anchored on the left then run through holes on the right (the picture is just the theory, not the actual placement of anything) The same would happen on the opposite side. The cracks are highlighted in red.

Thanks.
 
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Old 02-07-12, 07:05 PM
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Since you're in earthquake country, beefing up the footing with rebar and concrete would be a step in the right direction. And bridging the cracked corners at a 45-degree angle with reinforced concrete is a good idea. But instead of drilling concrete at the angles shown in the photo, it will be far easier to drill all holes at 90 degrees (going in perpendicular), then glue in some short rebar in every hole, let them develop strength for a few days, then beat on or bend the bars over (with a pipe cheater) to the 45-degree angle, lapping with each other and tied together with tie wire. I would use No. 5 or 6 bars, and drill the holes no larger than 1/8" larger than the rebar diameter. Don't forget to blow all of the drilling dust out of all holes after drilling, and use either a low-modulus epoxy or even a neat Portland cement slurry (grout) to glue the bars.

If you try to drill at the 45-degree angles, your drill bit will want to skid along horizontally. And should you be successful in drilling at the angles shown, it will not be possible to slip a single bar into adjoining pairs of holes unless one of the holes is drilled extra-long towards the outside of the footing, allowing the exposed end of the bar to be slid past the opposite footing face and then back into the corresponding hole.
 
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Old 02-07-12, 10:18 PM
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That is a really good suggestion. I was thinking to actually run the rebar all the way through the cracked part of the foundation to the other side and bend it into place to tie to the sides. I'm pretty good at drilling at an angle, but I think going straight in will be easier over all. I'll take the suggestion to ties the bars together, though, and hire someone to do it.

Do you think pouring concrete over the bars is necessary? Just the bars seem pretty adequate.
 
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Old 02-07-12, 10:24 PM
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Pouring the concrete over the rebar is ABSOLUTELY a must. The strength of the 'fix' is the concrete -- the rebar is only there to keep the fix from pulling apart.
 
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Old 02-08-12, 01:19 AM
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As lefty said, you need the concrete to complete the fix. Without it, your bars could buckle and pull apart when the big one hits, or your house will slide down the hill in a not-so-big-one, or at least crumble apart.
 
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Old 02-08-12, 02:56 AM
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The fix sounds good, but the existing crack on the corner was inevitable. It would have happened regardless of ground movement. The corner is a re-entrant corner, and concrete almost always cracks there. It's due to shrinkage during concrete curing/hydration and happens because concrete can't shrink around a corner. Take a walk around and look at any slab of concrete that is poured around a corner. The concrete, will have cracked there at least 75% of the time if not more. Re-entrant corners can include where concrete is poured around a column, at building corners, or anyhere the concrete is formed into an "L" shape. Do an internet search for "concrete crack" and "re-entrant corner" and see what comes up. you may not need the hyphen in re-entrant, I don't know. My point is that you probably have no real structural damage.
The other cracks you see may also be shrinkage cracks. If both sides of the crack are on the same plane (one side isn't raised higher than the other), then it's probably just a shrinkage crack where the concrete broke as it shrunk during curing.
 
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Old 02-08-12, 10:00 AM
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Hi, thanks for all the replies. I really appreciate the feedback. I was concerned because there had been a lot of flooding before I bought the house and got the drainage situation under control. The foundation is under 20 yo and there's no evidence of settling around the crack. That said, do you think I should go ahead with the reinforcement if these are really just cracks, or do you think I should just patch the cracks?
 
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Old 02-08-12, 10:49 AM
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another method would be to drill perpendicular holes and grout or epoxy in dowels. Instead of going through the bending and beating on them, lay bars at a 45 degree angle on them and then pour concrete. The concrete will make the bars work together and provide ties in all directions.

The further out you go from the corner, within reason, the stronger the connection or tie will be will be.

Dick
 
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Old 02-08-12, 12:49 PM
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If it were mine, I would do nothing. However, I'm not in a frequent earthquake area and I would have expected those kinds of cracks from the start. I see them all the time.
In your area, I would contact a building inspector or structural engineer and ask their opinion. Maybe there's some kind of extenuating circumstance or different set of problems in California than in Indiana. Remember, all I can see is one photo. Maybe there are other clues elsewhere that aren't depicted. An inspection could turn up something important that we can't see.
 
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Old 02-08-12, 01:00 PM
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Well, I just got a second opinion and he said to do nothing, though he suggested a french drain to give the water that pools up there somewhere to go. He took a good long look at the foundation and corroborated what you (Pecos) are saying, that the cracks are inevitable, and no matter what I do, I'll always have cracks. I do appreciate the feedback, though. It's good to know I can spend that money on a good floor and not have to sweat the foundation yet.
 
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Old 02-08-12, 11:33 PM
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variable,

Well yeah,it's concrete, and I can guarantee you 3 things about it -- it's gonna dry hard; it's gonna dry grey (assuming no colorant was added); and it's gonna crack.

The way I read your original question was whether to encase the rebar in more concrete or not. What I said (and BridgeMan45 confirmed) was 'yes -- encase the rebar in concrete. Otherwise, the rebar will just buckle on you if the stem walls move any more.
 
 

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