A question about vinyl plank vapor barrier

Discussion in 'Vinyl Flooring Q&A' started by dszafran, Oct 3, 2017.

  1. dszafran

    dszafran New Member

    Hey All,
    I'm an avid DYIer and have done several ceramic tile jobs from small bathrooms, entryways and kitchens as well as a few floating laminate floor installs.

    About to start a new project of laying vinyl plank flooring in my basement and could not find the answer to my specific question through Google so I figured it would easiest to just join and put the question out to the crew. I did the calcium chloride test on the slab it it came out at about 5.75 lb/1000/24hr, which is well within the specified limit of 8 lb/100/24h per the manufacturer. The question is whether I should lay a 6 mil vapor barrier over the concrete before laying the plank. The manufacturers instructions are silent about this. I'm not worried about the cost of the 6 mil plastic but more so whether it could cause issues in the future.
  2. Steve Olson

    Steve Olson Hardwood/Laminate Guru Charter Member I Support TFP Senior Member

    Is this a floating install or fully adhered?
  3. dszafran

    dszafran New Member

    This will be a floating floor with click installation
  4. Incognito

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

    The 5+ lbs of moisture vapor emmissions is fairly high and would proclude any glue down installation. Your next concern should be pH levels. Putting down some heavy plastic is standard with floating floors but what I'd be worried about is what happens to those emmissions under the vapor barrier down in a basement. Seems like it could get awful funky under there. On or above grade I've always assumed the moisture "wicks" out to the walls and dissipates in a reasonably healthy manner. Below grade I don't know if that's going to happen so mainly I would be worried about mold. Given extremely high pH readings there could be eventual consquences to the vinyl material in direct contact with the slab. But in general if your pH readings are moderate I would think you are better off without the heavy plastic sheet as some air passing through the planks is a good thing.
    • Like Like x 1
  5. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    One test isn't really enough to go from. The minimum number of tests per ASTM-F1869 is 3 for the first 1000 sq. ft. and 1 additional test kit for each additional 1000 sq. ft. But, even with the one you've done, you're getting a fairly high reading. As Incog said, that would preclude you doing a glue down installation in most cases. Hopefully, you followed the timing and directions for the test very closely. Mainly - Grind the spot the first day and open up the slab - come back 24 hours later and set the test - come back 60+ hours later and pull the test - weigh it accurately and calculate the result. Not trying to pick on you, but the industry is moving away from Calcium Chloride as a determining standard for acceptable installation because the test can be inaccurate even when done correctly. So, if even one step isn't done right then you might as well not do it, because it's not correct.

    Additionally, you should always do a pH test for each Calcium Chloride test site. You need to make sure you're using distilled water - not just bottled water - it must say distilled water along with an appropriate pH test strip or an electronic pH tester. Tap water as well as most bottled water contains free ions which can skew the pH result. The pH strips are usually included in the Calcium Chloride kit.

    Couple of other things. Moisture does NOT travel horizontally through concrete very far at all, maybe an inch or so at best. So, thinking that excess moisture finds it's way into the wall cavity isn't accurate. If the plate and wall cavity rest directly on the slab, then the moisture directly below the wall cavity will escape into the wall cavity but not from the floor out in the room.

    Incog is exactly right about the pH. If it's extremely high then you'll definitely want to use the 6 mil poly. Remember pH is exponential so with 7 being neutral a reading of 8 is 10 times greater than neutral, a reading of 9 is 100 times greater than neutral, etc., etc. up to 14 which is the max pH. A high pH directly in contact with the back of the product in a wet or damp environment can lead to the product cupping over time. The high pH can attack the plastic (vinyl) content on the bottom of the product and cause it to chemically react. Since no chemical reaction is occurring on top of the floor this is where the cupping comes from. One side contracts and the other side doesn't.

    If it were me, I'd probably use the 6 mil poly. As Incog said though you can have some musty odor and a potential for mold or mildew growth under that floor so the call is ultimately yours.

    Good luck with your project and wish you the best!
    • Like Like x 1
  6. dszafran

    dszafran New Member

    Thanks for the feedback. I should have been more clear about the moisture test. I did run three different tests in different areas of the space and they all came back in the 5.70 - 5.80 range. The kits did come with a pH test as well and I now plan on doing that tonight. Glad I asked the question because just about everything I've read so far about the pH level has been related to its impact on adhesives. Since I'm planning a floating install I didn't think it would impact me but, clearly, I was mistaken. Going back through the manufacturers specs I can see that they allow for a pH of up to 9.0.

    Thanks again!

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