Guidance for Slab On-Grade Moisture

Discussion in 'Floor Preparation' started by Alicia, Feb 21, 2019.

  1. Alicia

    Alicia Member

    This is my first post - I'm sorry it's so long, but we're kind of lost in our floor situation!

    We live in Florida and bought our house 5 years ago as a foreclosure with no disclosures. It's on a monolithic slab built in the mid 80's. The bank put carpet and pad on slab throughout most of the home, with new sheet vinyl on slab in the kitchen and baths. Last year, we replaced most of the flooring in the home with floating vinyl planks with attached foam backing (product is Syncore X, Eagle Creek collection, Long View Pine Embossed). We left the existing carpet in two bedrooms. We hired a professional flooring installer who sold us this product and installed it. This product went over 2 different types of surfaces -- directly on slab in 4 rooms and over the sheet vinyl in the kitchen and baths. Our installer said that a vapor barrier was not needed for this product, so one was not used.

    Recently we noticed that the appearance of the floor was changing (looks like cupping in wood floors). The installer came and pulled up a couple of planks and discovered moisture between the vinyl planks and the slab. He then opened up a small section in each room of the house. In the rooms where the vinyl planks are directly on the slab, the back of the planks had a white residue, smelled moldy, and both the planks and the slab were damp underneath. In the rooms where the planks are over sheet vinyl, the appearance was much better with just a slight white discoloration, a slight smell, and not much moisture on the floor or product. The installer brought a Tramex Concrete Moisture Encounter meter and tested every spot and they all pegged the meter over 6%. Now, three weeks later, most of the areas where the planks have been removed have decreased to around 4% using the Tramex meter. The installer said the levels were 1-2% when the floors were originally installed.

    We are trying to figure out what to do. We met with a foundation contractor about the slab moisture who said because we are in a low-lying area with no grade elevation, there's really not a way to move water away from or around our home. We have also met with a number of different contractors in mold remediation, tile, concrete, etc. over the past few weeks. We have lots of conflicting suggestions, so I am hoping someone can point us in the right direction. We have moved out of our home temporarily with our small children (due to the mold issue). We will be removing all the existing planks and sheet vinyl beginning this weekend and applying anti-microbial to the concrete to remove the mold. Suggested ideas for our next steps have been:

    (1) install 6-mil polyethylene vapor barrier and install new vinyl planks (concerned the mold/mildew will just collect under the plastic)

    (2) seal concrete slab with 2-part epoxy and install new vinyl planks (concerned the epoxy would eventually degrade - this is also very expensive)

    (3) install a dimpled membrane product like DMX 1-step/DMX airflow and install new vinyl planks and new carpet -- this person suggested maybe also doing an epoxy sealer before installing the DMX (the DMX website looks like the sealer would be unnecessary, but not sure if using only this product is going to work)

    (4) seal concrete slab with RedGard and then install ceramic or porcelain tile

    (5) seal concrete with other types of sealers (suggestions include MVR 8000, Bostik Slab-Cote, Bone Dry, xylene sealer) and install new flooring

    Thank you if you made it to the end of this long post! I look forward to any suggestions/advice!!!!
  2. Jon Scanlan

    Jon Scanlan That Kiwi Charter Member I Support TFP Senior Member

    I am a lino layer from down at the bottom of the world and do not understand a lot of your products
    I picked up on this

    Was there any problems with the vinyl in these areas when you moved in?
    What is the state of your new floor in these areas?
    I would have thought the existing sheet vinyl could have been a reasonable moisture barrier?
  3. epoxyman

    epoxyman Pro Member

    Shotblast and install Koster
    It will not degrade but it’s very costly
    We use it under 90% of our epoxy floors
    And also for others to lay wood floors over
    And yes I’m using it in Florida
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  4. Alicia

    Alicia Member

    Hi John, thank you. Yes, there was some bubbling in the sheet vinyl. The installer for the vinyl plank cut small holes to get it to lay flat and said the planks would be heavy enough to hold it down. I think that's why the planks in those rooms are in better condition, but not without any problems. Maybe if the barrier was seamless it would have worked? Between the sheet vinyl and the slab he used some kind of leveling concrete patching to make it level.
  5. Alicia

    Alicia Member

    Thank you.
  6. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    Redgard is not a moisture mitigation product.

    Whereabouts in Florida? I’m in Citrus County.

    Vinyl /plastic sheeting traps moisture, ceramic it could go through grout joints.

    I have to monitor interior humidity. This pollen is killing our allergies. Simply impossible to prevent migrating to interior.
    • Agree Agree x 1
  7. Jon Scanlan

    Jon Scanlan That Kiwi Charter Member I Support TFP Senior Member

    That confirms my opinion that there is a moisture problem in your concrete slab
  8. Incognito

    Incognito No more Mr. Nice Guy! I Support TFP Senior Member

    Shot blast and install Koster moisture control. It's going to be expensive but it will cure what ails you.


    Over top of that you can install pretty much any type of flooring with the proper/compatible underlayment. For resilient floors, laminate or engineered wood that would mean a Koster primer and a couple coats of cementitious floor patch (Ardex Feather Finish) There are cheaper alternative products available but the Koster and Ardex are worth the premium price. I promise.

    IMG_2018.JPG IMG_2023.JPG IMG_2030.JPG
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  9. Alicia

    Alicia Member

    Thank you. We are in Tallahassee.

    Thank you.
    • Like Like x 1
  10. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    I’ve got similar commercial bid going for removal. Customer put chair mats over gluedown carpet, mold grew underneath. They’re ripping it all out and putting porcelain plank. My recommendation is to use hydraulic thinset, aluminum silicate? And same type grout to prevent/reduce moisture migration. Then the moisture that gets through is controlled by dehumidifier which for air /allergies it should be done anyway. Moisture mitigating products by Mapei are various, not sheet membrane like water proofing, moisture vapor is what your controlling.

    Had a call the other day for a removal in Tallahassee, that’s a long boring ride on I-10.
  11. Alicia

    Alicia Member

    Thanks for the advice on the thinset and grout. Our initial thoughts were to install tile rather than new vinyl plank. Yes, I-10 is very boring!

    Thank you!
    Last edited by a moderator: Feb 22, 2019
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  12. Justin Lee

    Justin Lee Not A Fan Of Forum Process

    DO NOT use redguard. I did and it just pops up as well if hydrostatic pressure is high enough. I have been through the same only with porcelain. Literally, mind blowing. Have you found any solutions? I have lost sleep over the last 2 yrs because I invested so much money installing my large porcelain wood like tiles. I have consulted with 3 geotech engineer firms, 3 full leak detection tests, building scientist consultation, flooring experts and cant fins a solution. I even teied a radon mitigation system (subslab depressurization). Even thay didnt work. Im desparate
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  13. Alicia

    Alicia Member

    I am so sorry to hear about your situation! We don't have hydrostatic pressure at our house, just water vapor. Our slab tested at 100% relative humidity using probe tests. We ended up shot blasting the slab and then applying Mapei Planiseal VS (two-part epoxy sealer). Then we installed normal 6 mil vapor barrier and floating vinyl planks over it. We are still finishing up, so hopefully this will work. It's been a major pain (our family moved out of our house to an apartment) and VERY expensive (twice as expensive as the original floor installation cost). Good luck with your floors.
    • Like Like x 1
  14. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    Job we did yesterday I saw the product they’re using. Planiseal PMB. One thing as in everything tested are numbers, while yes water, what would be the amount of movement.

    Attached Files:

  15. M Mekkem

    M Mekkem New Member

    Moisture will suffocate if you put it directly on concrete, you need some air flow. Pretty sure there are a few options in the market

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