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I excavated my basement a couple of years back and I’m now in the process of finishing it. I’ve got a four foot kneewall about twenty inches inside the foundation wall. I’m thinking about spraying shotcrete on the inside portion of the fieldstone part, to stiffen up and seal everything. Nobody around here that I’ve talked to can tell me if this is recommended or worthwhile. Anybody out there have any suggestions
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If your fieldstone foundation was allowing ground water to pass through and you sealed it with shotcrete you would dam up water and create hydrostatic pressure. To resist this pressure you would have to add rebar or mesh before shotcreting. You might need a concrete strip footing to resist the lateral force at the base of the wall due to hydrostatic pressure.
I have been involved on three projects where brick/stone walls were reinforced with shotcrete. The engineer specified drilling into the brick/stone and epoxying in a #4bar (3' o.c.) to anchor rebar mat to the stone.
*James - I've used gunite on the outside below grade to do the same thing for waterproofing, but not on the inside. On the interior, we've done everything from repointing ($$$ - where visibility was important) to UGL coating. I'm guessing that you have no more than 4-5 feet of stone above the underpinning, so hyrostatic head shouldn't be too bad unless the water table is high. The primary reason to use a rebar mat as noted would be to keep the crete from cracking. It sounds like the water table isn't too bad since you don't report leaking between the stone and concrete.You probably have loose mortar and sand falling out of the joints and that is your primary concern. If so, I think that the shotcrete is a little overkill, expensive and messy. I'd use a thinner technique and paint everything white afterwards (if it's going to be exposed).Jeff
*The fieldstone foundation is only about 3 1/2 feet exposed with about 6" below the top of the kneewall.There is no problem with water. We sit on sand and gravel and have no moisture problems in the basement. The idea behind the shotcrete as Jeff mentioned is for the loose mortar and stone near the bottom of the fieldstone foundation. What would you suggest as your "thinner technique" Jeff.
*the problem I have seen when this is done is that the outer part of the stone wall still moves with the change of seasons and change of moisture content. this can ( actually did) lead to failure of the shotcrete on inside. if the new wall on inside has a drain under it, i would consider putting a thin framed wall in front of the stone wall , and finishing it with green drywall or even durock type product. you could even insulate it. if new wall has no drain, i would put a drain or channel in top of new wall and run to a sump or something to handle any water that may intfiltrate. i would the finish as above.
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I excavated my basement a couple of years back and I'm now in the process of finishing it. I've got a four foot kneewall about twenty inches inside the foundation wall. I'm thinking about spraying shotcrete on the inside portion of the fieldstone part, to stiffen up and seal everything. Nobody around here that I've talked to can tell me if this is recommended or worthwhile. Anybody out there have any suggestions