I’m currently building a new house with an active cellar in a room abutting an exterior wall. We have the wall and ceiling waterproofing and insulation worked out but are wondering what to do about the concrete slab. The slab sits on grade but it’s thick. The concrete floor of the house is built about 2 feet above the exterior grade. I’ve seen a few threads recommending water sealing and insulating slabs in basement cellars in cold climates. Does anyone have any recommendations for preparing a slab in a warm, humid South Louisiana climate in a room abutting an exterior wall?
In my basement slab (North Carolina) I sealed and used dri-core as the sub floor. I would probably seal and use some form of insulation.
I think insulation is going to be your big need. The slab is likely to be warmer than the (I assume actively cooled) cellar. So that means condensation on the slab probably won’t be an issue but it could/will be on the cellar side of the floor. I used dricore as well to make sure there was a little airspace between slab and subfloor. I would look into possibility of adding insulation above the dricore (though I see they have a new product that’s R-3) and below the flooring.
I just looked into the dricore R+ product and it looks great. Could I install a layer of NobleSeal underneath it? Alternatively, if I seal the concrete slab underneath the dricore, do you have any recommended sealants that I should use?
On another topic, do you have any recommended products for painting/waterproofing the stud cavities before the spray foam goes in?
Thanks for all the help!
Could you? yes. Should you? Not so sure . . . there is likely to be natural moisture coming up through the slab. You wouldn’t want to trap that between the Nobleseal and the floor. The Dricore is designed to allow a little ventilation underneath the subfloor so any moisture can escape. The NobleSeal appears to trap that very moisture.
Don’t think you need to waterproof the studs. Spray foam acts as a moisture barrier. You should use pressure treated lumber at least for the bottom plates.
You never want to create a moisture sandwich with vapor barriers. Everything that can get wet needs a path to dry. For the slab, that can be outside, but don’t have another air gap and something with low perm. The moisture will collect between and rot.
For the southeast, the ground isn’t doing you a favor for cooling so I agree with at least some insulation. I would plastic vapor barrier the floor with some foam insulation above it. Not foil faced, use the blue or pink xps. Seal or tie to the wall vapor barrier. Put the floor atop this.
Many cooling units require you to have a vapor barrier on the floor for warranty, as regulating humidity is very difficult if there’s a constant source. It would then run too much and die early.
Ask your concrete guy but Thoroseal is a commonly used concrete sealer. Now called Masterseal but guys in the trades still call it Thoroseal.
My contractor proposed installing Schulter Ditra on the floors as a moisture barrier. A layer of thinset is put directly on the slab, then the ditra material, then another thin layer of thinset, then tile. Does anyone have any concerns with this setup from a moisture-barrier perspective? Obviously, it won’t provide much insulation but the cooling losses through the floor shouldn’t be too significant.
I should add that there is a vapor barrier underneath the slab. But I wouldn’t think that has any affect on how I should moisture-seal the interior room.
DiTRA is fully waterproof when properly installed. I never checked the perm rating, but I believe it’s a near perfect vapor barrier as well.
It has a small air pocket between layers, so there’s probably some small insulation value as well.
There’s some worry you’d have trapped moisture between your under slab layer and the ditra, but as long as it’s not the full dimensions of the slab, it can probably dry out to the sides just fine, so I wouldn’t worry too much about that. You NEVER do that in a wall though as that’s just a recipe for mold.
Found the data sheet. Ditra is 0.006 rating for permeability which is near perfect for a vapor barrier.
Thanks, Anthony! You ant the other posters have been a huge help. I’ll follow up with some photos in a few months once completed.
having done some remodeling with schluter, i can say im not a big fan. i’ve heard good things about blanke.
if i was going to choose a brand right now it’d be laticrete or possibly blanke. ardex makes some very good specific products as well.
i just find schluter to be all marketing. too many idiots take their ‘training’ and the product/systems are only as good as who installs it.