Basement moisture vapor issues – would like to finish basement
I’ll try to make a long story short – I would like to finish the majority of my basement, it’s around 2700 sq. feet, will leave some unfinished for storage. Flooring would be either laminate or vinyl planks.
Newer house, less than 5 years old.
Climate zone 5
No vapor barrier installed under basement floor.
Dehumidifier has been running non-stop since the floor was poured – maintains about 45% RH in the winter, up around 50-54% in the summer.
Testing has been done (except for pH):
Average RH value of slab at 40% depth is 94% (tested in 5 areas)
Average MVER result of slab is 6.1 lbs/1000 ft (tested in 5 areas)
High sodium: 1700-1200 ppm, 1-3 mm below surface
High potassium: 2600-2200 ppm, 1-3 mm below surface
High chloride: 1091-1189 ppm, 1-3 mm below surface
Total 5512-4688 ppm, max level for epoxy is 1600 ppm… urethane is 4800 ppm.
I tried a sodium silicate sealer, it seems to have stopped some transmission as seen by objects placed on the floor no longer showing marks when moved or cardboard isn’t molding. This doesn’t help much in the expansion joints, and it seems like it may have caused a larger issue in possibly increasing those levels tested above. It did not impact the RH or MVER ratings at all!
I was looking into epoxy coatings, but the above sodium/potassium/chloride tests were all too high, risking delamination. The contractor states that a urethane product would be able to handle those numbers, but at 2x the cost of epoxy.
I’m looking at alternative solutions, I need to eliminate the vapor infiltration from the slab, but i’m not sure if that is completely necessary once the space is finished/conditioned. I’ve looked at dimpled membrane products like Delta-FL, DMX 1-Step, but am worried that if I don’t seal off the edges, they will not support an equilibrium within the air gap they provide, leaving the moisture to leak into finished areas with drywall or some other material.
I’m at a loss – am I forever doomed to have an unfinished basement, or is there some way to get this done besides tearing up the floor and installing the under-slab barrier?
I’ve read through this article, but it’s still not quite clear as to what I can do with the results above: https://www.buildingscience.com/documents/insights/bsi-003-concrete-floor-problems
I’d love to get 30 minutes with the author – I believe contributes here!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part