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Community and Q&A

Vapor Barrier Paint for Concrete

NICK KEENAN | Posted in Green Products and Materials on

I’m working on a house where the basement has a concrete floor with no vapor barrier. Is there a product that is a)meant for concrete and b) a class I vapor barrier?  All the products I’ve looked at that are meant for concrete don’t list a perm rating. The products that are meant as vapor barriers — primers — don’t list concrete as a recommended surface.


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  1. Expert Member
    NICK KEENAN | | #1

    So after I submitted this question the ad at the top of the page was for Liquid Rubber Multi-Purpose Primer. So I Googled it and it is recommended for concrete. Then I tried searching for a perm rating. I couldn't find it, but that search led me to Ames BWRF5 Water Base High Strength Elastomeric Liquid Rubber ( ) which is also recommended for concrete and has a perm rating of 0.016.

    Curious if anyone was experience with either.

    1. Expert Member
      NICK KEENAN | | #6

      Got this response from Liquid Rubber:
      "In response to your message, we don't have vapor perm ratings for our Multi-purpose primer as it is designed to be top coated with one of our sealants that do have perm ratings."

  2. Expert Member
    BILL WICHERS | | #2

    Google was probably watching you, and snuck that ad in to snag your interest :-)

    I've never used the Ames rubber coatings, but I have used epoxy. Epoxy works, but it can lift if there is too much hydrostatic pressure. It also won't adhere well if the surface is damp.


    1. Expert Member
      NICK KEENAN | | #3

      The basement is bone dry, the concrete is powdery on the surface. But that doesn't mean that vapor isn't passing through it, and I want to block vapor transmission. The problem is just about everything that is sold for basements is for waterproofing, and paint can be waterproof and have high vapor transmission -- like exterior latex paint for example. There are tons of basement waterproofing paints on the market but the Ames one is the first I've found that has a perm rating available.

  3. thegiz | | #4

    I didn’t read the Ames carefully but is it formulated to withstand foot traffic? If epoxy is a vapor barrier and floor is bone dry then it would work. Although I can’t find anyone that lists their perm rating for a epoxy product. I wanted to use a 1 part water based epoxy coating on my basement floor but was nervous about causing problems with trapping moisture and peeling. Although would it really matter if I cover it with something like padding or insulation? I’m assuming it can’t cause major structural damage to the concrete as I have read in some places

  4. HertzR | | #5

    Check out Laticrete’s epoxy coating product line. They have a couple products made specifically for this purpose. You’d have to contact their support line —which is really good by the way— to see what they say about leaving it uncovered and exposed long term for foot traffic, furniture, storage, etc.

    I am looking at using SPARTACOTE Moisture Vapor Barrier for my own basement (0.052 perms).

  5. thegiz | | #7

    I saw this ad today, not sure what this stuff is, says it made of elastromeric liquid or something like that. It is called semco and comes in a lot of colors, has a perm rating of .135 I guess that would be semi Impermiable Not sure if it is any good or anyone has used this before

  6. thegiz | | #9

    Thanks for link I read through the article, seems like redguard is recommended by code and is a class 1 vapor barrier. A classic article talks about the benefit of an adhered vapor barrier over poly. Epoxy is a recommended coating as well. Here is where I get confused, they mention you should never use any of this stuff if there is hydrostatic pressure. How do you know how much hydrostatic pressure you have, don’t you have to have like flowing water or seepage to have hydrostatic pressure. Also I don’t see how if for instance redguard or epoxy debonded it would make your problem worse. Is it better to leave bare concrete sometimes? For example if you put carpet pad, area rugs, or lvp over a sealed floor with epoxy or redguard and it debonded, does your problem become worse? I keep hearing that sealing your floor sometimes creates mold but how is that worse over bare concrete? Does this go back to the whole should concrete breathe debate? This is all assuming you are applying a top barrier in an older floor, where nothing exists underneath.

    1. Expert Member
      NICK KEENAN | | #12

      If you have liquid water entering your basement and you block it on the inside without providing a path for it to drain away then more water will accumulate and eventually find a place to go. That can make the problem worse. If enough water accumulates it can structurally undermine the foundation.

      The problem with liquid water intrusion is that it's often intermittent, it only happens under certain conditions. So it's hard to look at a basement and say it's never going to have a liquid water problem.

      But that's a completely different problem from vapor intrusion.

  7. Jon_R | | #10

    What is the reason for wanting a low perm barrier? It makes a difference as to how low you need.

    1. Expert Member
      NICK KEENAN | | #11

      To prevent vapor from wicking through the concrete and entering the living space.

      1. Jon_R | | #16

        > vapor... entering the living space

        Run the numbers for your case, but you should find that anything < 1 perm results in an insignificant amount of moisture (eg, 1 pint/day).

        The concrete alone should be about 3 perms, which isn't much moisture. Quite possibly less than the upstairs walls and ceiling.

        1. Expert Member
          NICK KEENAN | | #17

          The problem is finding products meant for concrete that have a published perm rating.

    2. thegiz | | #13

      Im going to use lvt or tile in a bathroom area and when you first walk in from back door. I think redguard makes sense there. The rest I was going to put lvp or use foam board with plywood. The area is very unleveled, so in meantime I was going to seal and use waterproof carpet pad with rug so kids can use until I fix the floor. When I asked manufacturer of carpet pad they said not to seal floor it would trap moisture and cause mold because it is difficult to adhere surface. Does that actually happen when stuff debonds or does vapor just escape. If it just debonds I rather seal it and worry about fixing it if it debonds. I’m just confused on how it could make a situation worse. I would think it’s worse just to put nothing. I also don’t know if I have hydrostatic pressure

      1. Expert Member
        NICK KEENAN | | #14

        Did you see my response #12 above?

        Hydrostatic pressure is a liquid water phenomenon. If you don't have liquid water dripping or oozing into your basement, you don't have hydrostatic pressure.

  8. thegiz | | #15

    I actually didn’t see comment 12 until after I replied. I guess I could use redguard as a liquid applied vapor barrier under tile, lvt, or padding since I’m not directly walking on it. I could use epoxy but I know redguard has a perm rating. I will still need to contend with condensation. I will use a dehumidifier but if area rug gets destroyed I will just toss it. There’s an article on here by Peter Yost where he has the whole basement in area rug but I don’t think he has a liquid applied barrier I just think he keeps it clean and uses a dehumidifier

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