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Old 12-07-2018, 06:13 PM   #1
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Basement concrete hydrostatic pressure issue


Hello wise people! I am going in circles trying to decide how to best proceed with my basement flooring project. We had decided on Drop and Done LVP (by xlfloorings), which is 1/4" thick, VERY waterproof, removable (not click in, not fully adhered), durable, and nice looking. Then we did our water test and found we exceed their 3 lb limit (we're at ~5.5). They recommend using a concrete sealant, then all's good. But they can't explain where that water vapor will go if we prevent it from coming into the home except that it will go to the sides and out. I think that means out into our wall space, which is already framed, insulated, and wallboarded - i.e., invisible and a potential mold factory.


Also problematic is that they don't recommend any insulation (even cork) under their product if we seal the concrete, which means a hard and cold floor.


There is another product I read about called Dricore (http://dricore.com/nw/subfloor_about.php) that is well reviewed - it is a hard dimpled plastic click-together that lets air flow under a vapor barrier. The only problem (besides price) is that it's hard to believe in a good size room (15x15') that the airflow under 1/4" dimpled plastic is enough to prevent mold.


We have never had any visible water on the floors, but have had mildew in basement closets.


I'd appreciate advice!
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Old 12-07-2018, 06:46 PM   #2
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Re: Basement concrete hydrostatic pressure issue


Check out Applied Technologies Inc. & this product Hydro Block.
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Old 12-07-2018, 06:54 PM   #3
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Re: Basement concrete hydrostatic pressure issue


HI Clarence, That product looks great! Wish we had done that before building the walls. Now we need a way to prevent all the slab vapor from moving laterally then into the walls where it can't get out.
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Old 12-07-2018, 07:11 PM   #4
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Re: Basement concrete hydrostatic pressure issue


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HI Clarence, That product looks great! Wish we had done that before building the walls. Now we need a way to prevent all the slab vapor from moving laterally then into the walls where it can't get out.
Call the TECH support and ask what they would recommend.
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Old 12-07-2018, 07:14 PM   #5
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Re: Basement concrete hydrostatic pressure issue


You should have a perimeter drain at the footing level outside and that would keep water below the floor level. If that is not working nothing painted on the surface will help.
Tape 12" squares of poly on the floor and make sure it is seals and leave them for a day or two to see just how much is coming up under the poly. And see where to go from there.
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Old 12-07-2018, 07:48 PM   #6
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Re: Basement concrete hydrostatic pressure issue


I have done a water test, which is how I know we have ~5.5 lbs (/1000 sqft/day). Tech support is who suggested sealing the cement, but they also said that would protect their product but not necessarily the insides of our walls from mold. He said "I'm not a builder." They thought the Dricore would work fine, but didn't know of the product, so I'm leaning that direction but appreciate the help and discussion.



I don't know if we have perimeter drains that are working. We live on a steep ridge and my guess is there are no drains except a french drain on the uphill side. In fact, it's a daylight basement with the back half hanging over the ridge. So far, everyone's been surprised we have any measurable hydrostatic pressure since it seems the water ought to all flow downhill a lot easier than coming up through our slab....but we did the CaCO3 test and that was the result. It must take a long time to seep through the hillside.
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Old 12-07-2018, 08:01 PM   #7
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Re: Basement concrete hydrostatic pressure issue


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Originally Posted by jsand View Post
I have done a water test, which is how I know we have ~5.5 lbs (/1000 sqft/day). Tech support is who suggested sealing the cement, but they also said that would protect their product but not necessarily the insides of our walls from mold. He said "I'm not a builder." They thought the Dricore would work fine, but didn't know of the product, so I'm leaning that direction but appreciate the help and discussion.



I don't know if we have perimeter drains that are working. We live on a steep ridge and my guess is there are no drains except a french drain on the uphill side. In fact, it's a daylight basement with the back half hanging over the ridge. So far, everyone's been surprised we have any measurable hydrostatic pressure since it seems the water ought to all flow downhill a lot easier than coming up through our slab....but we did the CaCO3 test and that was the result. It must take a long time to seep through the hillside.
There is a difference from pressure pushing it up and moisture wicking up. If it is just wicking the heat in the room adds to that, behind you wall insulation might not be a problem.


I would drill a few holes in the deepest part of the basement.to see if you have water pushing up. Then you could pot a steel rod down there and see how deep the water might be. You would expect water to be 4 or 5 inches below the bottom of the concrete. While it is raining would be good.
You might want a sharpened stick handy in case you do.
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Old 12-07-2018, 08:09 PM   #8
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Re: Basement concrete hydrostatic pressure issue


Oh! Never thought of that! I can do that test - I think it's supposed to start raining next week. Are there different outcomes if I find the water nice and deep? Less to worry about?
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Old 12-07-2018, 09:05 PM   #9
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Re: Basement concrete hydrostatic pressure issue


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Oh! Never thought of that! I can do that test - I think it's supposed to start raining next week. Are there different outcomes if I find the water nice and deep? Less to worry about?
I f the water is deep then you might loo at the floor sealer and maybe plywood over 1" foam board to keep the heat away from the concrete.
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