Effloresence in Basement

[SamanthaAB]

We're just beginning to finish our basement but have noticed for the past couple years some efflorescence coming up beside the mats we have sitting on the basement floor. House was built in 2007 in central Alberta in an area that has a high water table, we have a sump pump that goes regularly once the ground thaws and we have our downspouts away from the house.

I'm not sure what we should do about it, we've found conflicting articles about in online and have been given different advice from other people, from covering the floor (after cleaning the efflorescence away) with acrylic paint, waterproofing, dricore, and doing nothing. We also will be hooking up our in-floor heat and don't know how that will affect it. We bought Behr Interior/Exterior Low-Lustre Sealer but haven't applied it yet because we don't know if thats what we should use.

Edited to add pictures and mention if we lift up the mats, the floor and bottom of the mats feel moist.




Any advice would be greatly appreciated.

[dlarrivee]

I would throw a 2' square chunk of 6mil on the floor and see how much moisture drive there is before buying anything.

[Dana]

This is a heated, insulated slab?

Moisture coming through the slab in the middle of the slab is an indication that it was built without a vapor barrier. Silane/silex based masonry sealers can reduce the capillary draw by quite a bit, somewhat better than acrylic sealers, but it's still not good enough to protect a wooden subfloor or rug. Paints will eventually blister and peel from the vapor pressure with acrylic-only sealers. The heavier duty epoxy sealer/vapor barrier treatments can make it dry, but for a price. eg: http://sealgreen.com/e10-epoxy-concrete-sealer.aspx Surface prep prior to application is still everything, in terms of getting it to bond well though.

But if there's that much moisture under the slab, the thermal conductivity of the soil is going to be high, and a heated slab may be pretty lossy to the ground compared to places with dry soil.

Before fully finishing out the basement you may need to slip a capillary break between the bottom plates of the insulating studwall in that picture, unless it already has a pretty-good sill gasket or something.

The rubbery closed cell mat floor coverings are highly vapor retardent as well as somewhat insulating, which is why it gets wet and stays wet below them. The R-value keeps the bottom side temp lower, which lowers the vapor pressure relative to the room air, and the high vapor retardency doesn't allow it to dry toward the room.

[johnfrwhipple]

I used drycore in my North Vancouver basement renovation years ago before we renovated the whole house and when we removed it and the click and lock flooring the floor was soaked. Is your home older? Mine was built in the 60's and has no poly under the slab.

We have yet to work on the basement of my home since we renovated and as an experiment I used 1/4" cork in my mudroom. The plan was to created a thermal break for floor heat but since adding the cork the room is quite warm unheated. I set the cork 2'x3' panels with a premium white thinset from Laticrete 255 and because of the colour might be hiding the fact that moisture is breathing through the panels seems.

I have been using Grani Rapid from Mapei with great success to set regular blue insulation rigid panels and perhaps you could install some of this and seam the sheets with a product like Kerdi Fix. Once the basement is heated it will draw moisture to the surface.

Do you have proper exterior drainage and rain water leaders?

JW