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Community and Q&A

Partially Finished Basement Plan

PLIERS | Posted in General Questions on

Hope everyone is doing well. So I’m putting my basement finishing on the back burner because I’m spending money on some structural repairs. I want to leave my basement unfinished but make it look nicer for kids playroom. So let me know if anything is wrong with my plan.

-I’m skimcoating my basement floor so it is level and clean, I am also resurfacing the walls with concrete in some spots that need repair. I’m then going to paint everything with 2 coats of white drylok and leave it bare

-On the floor I’m putting foam interlocking mats. I will be taking them up every few months to clean and check for any water

—The rim joist I’m going to spray with closed cell spray foam, I was going to buy one of those spray kits don’t know how hard that is for diy

-As some final touches just going to add a door in front of electrical box, close off mechanical room, and add 2 more doors. Also run my dehumidifier at 75%

Is there anything wrong with painting walls and floor with drylok? This is all going to help me finish it later with insulation and drywall. If it stays comfortable might leave it like this for a while.

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  1. Expert Member
    Michael Maines | | #1

    Joe, what climate zone are you in? Do you have insulation between the first floor joists? In cold climates, people usually underestimate how much heat loss occurs through uninsulated concrete walls. There is usually a decent return on investment for insulating the walls. But if you're committed to not insulating:

    Keep a close eye on the floor mats. Here in climate zone 6, uninsulated slabs can be 50°F or colder. If the air on the main level is 70°F and 50%RH, not unusual numbers, at 60°F it will be about 70%RH and will condense at 50°F. You can also get moisture coming up through the slab, trapped by the foam mats. You might be fine--many people are--just keep an eye on it.

    You can use a froth pak for your rim joist but it's a serious health hazard and all of the froth kits I know of use blowing agents that are potent greenhouse gasses. It would be worth pricing it out with a pro who can spray HFO-blown foam, which has a much lower impact.

    Drylok is a good product. I've seen it stay adhered on pretty leaky walls for 10+ years. Hydrostatic pressure is relentless, though, so it will probably fail eventually.

    Setting your dehumidifier at 75% is pretty high. Most building science experts recommend keeping RH below 60% at room temperature, but that's about the same as 75% at 60°F. Air at 60°F and 75%RH will condense on surfaces less than about 52°F.

  2. PLIERS | | #2

    Hi thanks for the advice. I’m in climate zone 4a, I’m in the suburbs of New York City. So hot and humid in summer, winters cold but not extreme. Yes the insulation would be worth the investment but I’m not fully confident in the moisture levels of old 100+ year old home. Walls are stone and mortar with a layer of concrete over it. When I first moved in had to rip out a finished basement with black mold everywhere so a little reluctant to finish. I’m sure if I follow advice here I could finish it properly but right now I’m planning a large renovation so closing walls might be a hassle later on. Insulating the rim joists I think would make a difference even if walls are not insulated and finished. Space I’m trying to use for playroom is about 10x22. Ceiling is low as typical in an older home. It shouldn’t be too much of investment to refinish some of the concrete. Is there a better option for floor? Maybe raised plastic tile would be safer choice than foam. What about a vapor barrier like delta fl or similar taped and sealed under temp floor?

    1. Expert Member
      Michael Maines | | #3

      Joe, we just had a pretty thorough discussion about a similar floor situation here:

      Mold thrives with temperatures between about 40-50°F and 85-90°F and a source of moisture. It can find food almost anywhere. The elements you can control are surface temperatures and moisture, including the moisture carried by the air. Drylok should help with moisture coming through the walls and floor for the short term, but that leaves temperature and airborne water (i.e., humidity) to worry about.

  3. walta100 | | #4

    Remember it is a code violation to put anything directly in front of the electrical panel. As I recall you need 18 inches to the left and right and 36 inches in front.

    Did you test the concrete for moisture by taping plastic down for a few days?


  4. PLIERS | | #5

    Is it possible to put down LVP before I insulate and build my basement walls? I’m thinking drylok floors, add 6 mil poly, and then put lifeproof lvp on top. Leave a 1/4in gap between concrete wall and floor. What do I seal the gap with? When I am ready to insulate walls I’m thinking rigid foam against wall and use furring strips to attach drywall so I don’t need to screw bottom plate through lvp. Trying to finish floors first if I need to leave walls open for now. A temporary floor might be useless and a waste of money if I can find a way to finish my floor first.

  5. Expert Member
    NICK KEENAN | | #6

    There are at least four sources of moisture in basements:
    1. ground water coming up from below.
    2. Rainwater coming down from above.
    3. Moisture wicking through the masonry walls.
    4. Humidity condensing out of the air onto cool surfaces.

    Drylok is a good product. It will cure #3. It won't help at all with #4. Depending on the severity it may help with #2, similarly with #1 but less likely. The danger with waterproofing from within with liquid water (#1 and #2) is that if you give the water no place to go it can become trapped behind your basement walls. Water is quite heavy, and it will start exerting a sideways force on the walls, which they are not designed to resist. At best this will cause the Drylok to blister and come off, at worst it will cause the wall to bulge or collapse.

    So the first step is to figure out what kind of moisture you're dealing with. If it's liquid water -- #1 or #2 -- the real solution is perimeter drains below floor level to take the water away, and a loose rainscreen along the wall that allows the water to flow freely into the drain without any chance of buildup.

    While Drylok will help with #3, it's kind of overkill, because so will plastic sheet or foam insulation.

    For #4, insulating the walls will help eliminate cool surfaces, and dehumidifying the air will reduce indoor humidity. Air sealing the basement will reduce the amount of work the dehumidifier has to do. Drylok will air seal the above-ground portion of walls, but so will plastic sheeting.

    So the answer is, there's no situation where Drylok is the best solution.

  6. PLIERS | | #7

    I’m almost sure #1 is my problem because slab has spots of moisture or dampness regardless of season. If I were to put in a perimeter drain would I still be able to semi finish it, put flooring with walls open. Will drylok only on the floor still cause wall buckling or damage? Can I paint concrete wall with 100% acrylic paint or some other material that will not block the moisture to escape? Function is my number 1 goal with aesthetics somewhere in there.

    1. Expert Member
      1. PLIERS | | #10

        Thanks for article, I read both. So I have 2 points from article and something that was said:

        -If you bury your waterproofing treatment behind finished floor and walls such that they cannot be inspected for new cracks, there is no guarantee that your waterproofing system will stand the test of time.

        -they tested 3 products Koster sealed concrete with no water leaks.

        So NSW should not be your primary defense but there are products that test well. Plus you can’t cover your walls with insulation and Sheetrock because you would have to be able to inspect cracks and reseal them. DC also pointed out worse case scenario you trap water and walls burst or collapse so I don’t want that.

        So at the end of the day I’m left confused still. I’m building an addition in about 2 years so part of the process will be digging on side of house so my water/moisture problem can be addressed. I can live with heat loss with uninsulated walls and I can live without the beauty of Sheetrock. I just want to seal my walls and floor with something safe. Lighten up the room with white concrete. I don’t want my walls to explode from water pressure and I can keep up with the maintenance of checking for water and moisture. My uncle lives a few streets down, does not have a stitch of insulation, except a popcorn ceiling and it doesn’t ever seem cold down there. He paints the walls every year, checks for peeling, scraps off and starts again. He even has cheap area rugs on some spots that he just tosses or washes periodically. I mean it’s not perfect or hgtv worthy but he goes to bed every night and doesn’t worry about mold or exploding walls. There has to be a safe product to use to seal and lighten up concrete. And yes I will ask him what he uses for paint but I doubt it is a green solution.

        1. Expert Member
          Michael Maines | | #11

          Joe one traditional approach is to use a lime mortar wash on the interior, "whitewash"--it's a sacrificial layer that will flake and peel over time but you just keep repairing it as needed. It protects the existing masonry from spalling as well.

          Many approaches CAN work, and often do. But when you're asking for advice on a green forum, we're going to do our best to tell you ways that are most likely to not result in problems.

    2. Expert Member
      NICK KEENAN | | #9

      The problem with trying to deal with water infiltration from the interior is that unless you give it somewhere else to go it's going to find another way in.

      Rather than thinking of it as finished vs. unfinished, I think you should think of this project in five stages:
      1. Water management
      2. Moisture sealing
      3. Air sealing
      4. Insulation
      5. Finishing

      Note that steps 1-4 are now required in new construction for an unfinished basement. Just sealing the space against air and water leaks will make it much more comfortable.

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