Hi. I own a bungalow in Minneapolis, MN built 1921 with a poured concrete foundation. I am finishing 1/2 of this basement as a legal bedroom, and wish to put in drywall walls and ceiling. My wife and I have lived here for seven years, and have had nary a drop of water leak through the foundation and into our basement. No mold or mildew problems, either, though it can get humid down there in the warmer months, for which we use a dehumidifier.

The room we are finishing was your typical Midwest basement bar when we moved in, and the walls were nothing more than 1/4″ thick cedar closet board tacked to furring strips attached to the concrete foundation with masonry nails.

I just finished tearing out the last of this stuff and am noticing that there is one corner of the basement where the concrete walls seem pretty soft, to the point where I was able to scrape a 2″ gouge into it with the claw of a hammer without too much trouble. The walls are also rather damp at the very bottom, to about 1.5′ up, for a length of about 3′. I want to clean these walls up so that I can attach 2″ XPS board all the way around as an insulated vapor barrier, and understand that these need to be attached to the concrete with construction adhesive (PL400 or something similar). This wall also had a sacrificial layer of concrete skim-coated across the lower two thirds to make it look pretty, and I’ve already scraped off all of the loose stuff (i.e. nearly all of it.), as well as any efflorescence/surface blisters.

I of course need to make sure that the adhesive will hold, which means I can’t be attaching them to a dusty, crumbly surface. I realize there are concrete sealers and hardeners out there (Drylok, SaniTred, RadonSeal) to help stabilize the concrete and keep moisture at bay, but I know that anything applied to an interior, without waterproofing the exterior, with only last for 5-20 years depending on the product. Waterproofing or wrapping the exterior of our foundation is not an option at this time (we spent a lot of money already on the egress window for this basement room and other home improvements this year), so I need to figure out something for the interior.

Once the insulation board is up, I want to hang the drywall on furring strips that are attached to it, so I can’t run the risk of the insulation board separating from the foundation eventually.

So…what is my best course of action with this foundation issue?

Thanks for your time and suggestions!

*UPDATE*

So, here’s something crazy: Looks like I’m not going to insulate the basement at all. As it turns out (according to Minneapolis code, anyway), insulation is not required for refinishing an existing basement into habitable space. It’s not that I don’t want to, though. It just seems that I shouldn’t. Check this out (from the City of MPLS website):

“Cover a northern quadrant of the interior bare basement wall (floor to sill plate) with clear 6-mil. polyethylene such that the polyethylene extends at least 10 ft along each wall away from the corner. Seal the polyethylene edges only to the wall, sill plate and floor with appropriate sealing tape or construction adhesive….observe the polyethylene for a period of at least 2 weeks. If the wall surface becomes wet or any condensate that has collected on the interior surface of the polyethylene does not evaporate or drain away, then the wall is by definition wet and interior insulation of any kind should not be installed on the walls of that basement.”

I know for a fact that the bottom 2-3 feet along the west and north wall had areas where they were consistently damp to the touch, even though most of it has now been parged over with a thin layer of masonry concrete and Drylok (which I only used on the lower half of the wall). While it’s too cold now to do a soak test (where you soak the ground next to the foundation for awhile to see if and how it penetrates the foundation wall), I feel like I shouldn’t even take the chance with insulation, especially because the rest of the basement isn’t insulated. I mean, the basement never really gets that cold, anyway, and is always comfy and cooler in the summer (though I do have to have a dehumidifier running constantly to keep it between 50-55% humidity, otherwise it’s around 75%. BTW, I’ve done everything I can on the exterior to make sure rainwater drains away from the foundation. I should also add that exterior insulation on my foundation is not an option.

Basically, there’s no way in hell I’m going to take a chance with a potential mold problem.

Two additional questions, then. First, should I use treated wood studs in addition to treated wood for the sill plate because I’m putting a wall over uninsulated concrete? Also, should I use regular sheetrock or the water and mildew resistant stuff with the green paper backing?

Anything else I should do before building these walls over my uninsulated foundation walls?

Again, many thanks.