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Addition Slab Lower Then Original

 
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Old 01-18-2012, 01:03 AM   #1
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Addition Slab Lower Then Original


Looking for any tips from anyone who has dealt with this before. New basement slab is 13" below existing slab water is seeping from between the existing slab and footer (which was underpinned with new footing at new foundation level) each slab has its own draintile and sump pump my question is how to seal this joint and handle the water issue. The design would allow me to pour a concrete step along the entire wall above the joint with the idea that path of least resistance would again become the draintile of the higher original slab i have seen some sealents that are designed for bonding two slabs in this manner or should i just use a sealer at the joint of original slab and footing or do you think i need to run a drain tile under the old slab and tie into the newlower sumpcrock
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Old 01-18-2012, 04:02 AM   #2
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Re: Addition Slab Lower Then Original


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Originally Posted by peakecg View Post
Looking for any tips from anyone who has dealt with this before. New basement slab is 13" below existing slab water is seeping from between the existing slab and footer (which was underpinned with new footing at new foundation level) each slab has its own draintile and sump pump my question is how to seal this joint and handle the water issue. The design would allow me to pour a concrete step along the entire wall above the joint with the idea that path of least resistance would again become the draintile of the higher original slab i have seen some sealents that are designed for bonding two slabs in this manner or should i just use a sealer at the joint of original slab and footing or do you think i need to run a drain tile under the old slab and tie into the newlower sumpcrock
You have to provide a channel embedded in the concrete or block to allow water pass externally from under the upper portion of the slab to reach the lower portion of the lower slab and provide drainage to divert the water to the sump on both levels. It's a mess of a job now since its already built and in place...the genius who did this should have thought about this during construction, because it is obvious that the water from the higher point will always find a way to penetrate into the lower point. Since under pinning is in question, you have undisturbed soil under the upper slab and you have the same surrounding the lower slab, where now the lower slab became a basin and takes all the water from the top, not to mention from underground water table if present...and when you get the rain and the seasonal water table rises, hydrostatic pressure pushes the water into the cracks because its finding ways to escape and there is no better way then using the voids in or between the the two slabs.

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Old 01-18-2012, 03:31 PM   #3
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Re: Addition Slab Lower Then Original


WOW! Now that sounds like a real mess. Pics would be cool to see...
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Old 01-18-2012, 03:39 PM   #4
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Re: Addition Slab Lower Then Original


A combination of the 3 solutions you mentioned may be your best bet at this point, depending on what you want as a finished product and how far you're willing to go to get there. I've run into similar situations before. Good luck!
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Old 01-18-2012, 04:19 PM   #5
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Re: Addition Slab Lower Then Original


Thanks for the input i think i agree that the upper drain tile needs to be tied into the lower which wont be too hard at this point. I'm thinking the joint still needs to be sealed would you use a flexible sealent or a hydraulic cement? As for the genius who built it, i am the gc but neither the architect, structural engineer, soil engineer, foundation contractor put any detail on the drawings or raised any issues. If we all had perfect foresight like you we probably wouldnt need this forum

Any one have a detail on how you would install the draintile if you were pouring a two level slab from scratch? I may be able to replicate
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Old 01-18-2012, 05:30 PM   #6
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Re: Addition Slab Lower Then Original


http://www.masco.net/pdf/catalogs/fo...es_page221.pdf

Bentonite waterstop RX

Oddly enough have used this on a underpin along with Volclay panels.

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