Moisture Barrier over Concrete Slab

GreenDog194January 18, 2013

We plan to install strandwoven click together solid bamboo floating floor over a moisture barrier on our ground floor concrete slab. The slab was installed in the 50s. It is not insulated and it does not have a plastic membrane or anything between it and the ground. We have not really had any moisture issues, but we need a moisture barrier for the warranty and want to play it safe.

We want to know if the moisture barrier fabrics that are used under tile would be a good choice. We would mud down the fabric and apply the wood on top with the required 1/16" or less pad between the fabric and the wood. We would follow the instructions for installing the tile moisture barrier, but not apply thinset and tile on top. Here are some the products we might consider:
NobleSeal TS, Thin-set waterproofing membrane; Dal-Seal TS (Dal-Tile Corp.); or the Schluter Kerdi or Ditra product.

We did investigate the plastic dimplemats. We tried a 1/2" thick dimplemat product by SuperSeal. It sounded like rice crispies when walking on it, although the dimplemat was sandwiched between garden cloth and the 1/16 foam floor pad. We will try the Superseal "warm and quiet" product next. However the bamboo requires the underlayment to be no more than 1/16" to prevent the click together floor from creaking or flexing. We'd probably have to put plywood on top of the Superseal dimplemat, which presents a height challenge.

Hence, we are hoping that the CPE tile isolation membrane will provide the moisture barrier we need without needing to add more height with an additional plywood layer.

Our flooring needs a vapor barrier with a perm rating of .13 or less for warranty. The Nobel has a perm rating of maximum 0.15 perms, but I'm not sure if I found the right specs. What I found was for steam room testing (ASTM E96/E96M, Procedure E uses the desiccant method at high temperature 100 deg F ). Kerdi has a perm of .75, according for the customer service, but I don't know what they were testing.

Any recommendations? Any thoughts?

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Sophie Wheeler

You are completely overthinking this. The cushion requrede by a floating floor install acts as the moisture barrier. If you are paranoid, then just tape down a layer of 6 mil poly under that, sealing the seams with real duct tape.

    Bookmark   January 18, 2013 at 7:04PM
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I usually do overthink things, and if I don't I always seem to end up paying for it!!

We met with an installer today and he really likes the NobelSeal product. He says we don't need to thin set it down, or glue it down. It is a great barrier and using the Nobel sealing product, the seams will stay closed. He doubted that 6 mil poly would stay sealed with duct tape over the years.

    Bookmark   January 18, 2013 at 9:31PM
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If you want to spend 10x the money you need to spend doing the job, knock yourself out. At those prices though, I'd do a painted on moisture barrier like RedGuard or HydroBan. Or just do a glue down with a polyurethane moisture barrier glue. It will be quieter underfoot with a glue down as well.

    Bookmark   January 19, 2013 at 1:38PM
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Hi GreenDog - posters are right. You don't have to go to that expense. Below is from Home Depot. I just used it under cork flooring that we laid (DIY) on ground floor, cement slab. It's 6mil, 14 bucks a roll.

Roberts Moisture Barricade 120 sq. ft. 12 ft. x 10 ft. Underlayment

    Bookmark   January 21, 2013 at 1:21AM
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Wow, thanks for the recommendation! I could put down plastic without any mastic below it? I also see that you wrapped the plastic up the walls a bit. My contractor wants to leave it away from the walls -- to breath. Breath what -- moisture? Where -- up my walls and on my floor? I'd really like to do your method, but perhaps I should not in rainy Seattle.

Here is what I found about prescribed methods per the hardwood flooring trade ass'n:

Copied from NOFMA Publications

Two membrane asphalt felt or building paper system.
Prime and apply cold cut-back asphalt mastic
with a notched trowel at the rate of 50 sq. ft per gallon.
Let set 2 hours. Roll out 15 lb. asphalt felt/building
paper, lapping edges 4". Butt ends. Over this apply a
second similar coating of mastic and roll out a second
layer of asphalt felt/building paper. Lay both layers
of felt in the same direction, but stagger the overlaps
to achieve a more even thickness.


Polyethylene method. When slabs are well above
grade and the expected annual rainfall is light to moderate,
cover the entire slab with 4- to 6-mil polyethylene
film, overlapping edges 4-6" and allowing enough
to extend under the baseboard on all sides.


Where moisture conditions are considered more severe,
prime and apply* cold-type cut-back asphalt mastic with
a straight-edge or fine tooth trowel over the entire slab
surface (100 sq. ft. per gal.). Allow to dry about 1 hour.
Lay the 4-6 mil polyethylene film over the slab, covering
the entire area and lapping edges 4-6". "Walk in" or roll
in the film, stepping on every square inch of the floor to
insure proper adhesion. Small bubbles are of no concern,
and may be punctured to allow captive air to escape.


Installing Screeds
Sweep the slab clean, prime with an* asphalt primer
and allow to dry. Apply hot (poured) or cold (cut-back)
asphalt mastic and imbed the screeds. Stagger joints and
lap ends at least 4"and leave 1⁄2" space between lapped
edges. Be sure there is enough mastic for 100% contact
between screeds and slab. Leave 3⁄4" space between ends
of screeds and walls with a continuous run of screeds at
end walls.
Over the screeds lay a 4- to 6-mil polyethylene vapor
retarder with edges lapped over rows of screeds. Avoid
bunching or puncturing it, especially between screeds.
The finish flooring will be nailed to the screeds through
the film.


Here is our difficulty with pain on products:

(1) My contractor was burned using one in the past and doesn't think he would have any recourse to the mfg warranty if it fails for us.
(2) I have a bit of potential mastic with asbestos stuck to 1/6th of the floor that they don't want to grind off.
(3) They say shotblasting is too messy now that drywall is up.
(4) They say there is no way that my old 50s slab has the proper PH or chemical composition uniformly to provide proper adhesion for the trowel on waterproofing goo.
(5) My contractor's sub, the flooring installer, does not have a shotblaster and can't do that prep work.

If I just had the right contractor, he would have found the right solution, provided a warranty, and not involve me! Too late to switch horses.

    Bookmark   January 21, 2013 at 11:46AM
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You are again way over-thinking this. The installation method you've copied, pasted and commented on are for installing solid nailed down wood floors.
As another commenter pointed out, a layer of 6 mil poly is sufficient as a moisture barrier. If you doubt the efficacy of 6mil poly, buy some 8 or 10 mil poly. It generally comes in long, fairly wide rolls so there will be very few joints. Any joints can be overlapped (or folded) and taped with duct tape or (my preference) heavy duty packing tape. Lap it up the walls and cut off the excess once the floor install is complete.
And by the way, since you find it necessary to yell about the chemicals you don't want in your house, do some research on what's in your chosen strand woven Bamboo.

    Bookmark   January 21, 2013 at 2:09PM
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Thanks for the reassurance about poly. Glad you think I can do something as simple as poly.

I did not mean to yell with all caps -- could not figure out how to set apart comments to the instructions. I see that brackets would have done a better job!

I sourced the bamboo at a greenhome supply store, and it is supposedly as free of chemicals as the stuff gets. I thought I had to still treat it with the same care as wood, since it is not an engineered material, but solid strand woven that clicks together.

    Bookmark   January 21, 2013 at 8:40PM
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If your bamboo is anything like a solid sample I picked up at HD, I don't think you could have any problems. I stuck one end in a bowl of water for a day or two -- moisture wicked up and discolored it badly. After it dried out totally, I could not tell that it had ever been wet, still solid and original shade. Engineered floor samples I did that to fell apart.

    Bookmark   January 22, 2013 at 1:00AM
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I've read that lots of Bamboo has formaldehyde in the binding glue.
Personally I'm not all that concerned about it because many products have it in there naturally.
Good luck!

    Bookmark   January 22, 2013 at 2:43PM
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Thank you for the tip on the experiment! The retail supplier (Greenhome Solutions) says this is the product that they sell the most, and they have sold it for a long time. They said they've seen it hold up to house floods. Sounds like similar results to your bowl of water experiment!

I have requested from the distributor the product's final MSDS sheet on added urea formaldehyde -- I realize that stuff exists naturally in wood, I just want to avoid more of it. There are probably worse things I should check up on, but media has done a good job about slamming formaldehyde and I'm their target sucker for that sort of info.

    Bookmark   January 23, 2013 at 10:17AM
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I received the MSDS for the flooring. The floor does contain phenol-formaldehyde in the resin, but the good news is that this is not the toxic Urea Formaldehyde. It is considered a NAUF (no added urea formaldehyde) product.

The product I selected is manufactured by Teragren: which has a reputation as a responsible manufacturer. Here is the MSDS for their Synergy Woven Bamboo: . It looks more or less identical to the TAS EVOStrand solid bamboo.

The distributor did additional investigation: T&A Supply Inc. has evaluated formaldehyde emission rates from its products (typical range of 0�0.015 ppm) and found these rates to be below the no significant risk level that would require product warnings.

If you are looking for a NAUF product, looks like this is an option.


    Bookmark   January 25, 2013 at 12:36AM
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I've been installing Teragren since before they called themselves "Teragren". You chose a fine product.

    Bookmark   January 25, 2013 at 10:41PM
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Well, its been almost 6 months since you posted about your Bamboo - how did it go and how is it holding up??? We installed 1000 feet of this exact product in Nov 2012 - we are currently in the process of pulling it all up,, YUCH... moisture issue???? not really sure what happened,,, installer is being real good and standing behind it all - the house is 1/2 up and the rest is coming out tomorrow.. going with eng Hickory in its place - also laying down a very expense moisture barrier (painted on) Only used Glue that was suppose to have a moisture barrier in it??? floor was 14 years old in Central CA - maybe 10" of rain a year and NO problems in the past... anyway,, moisture test is in progress at this moment - Wish you luck with your Bamboo - wife liked it but it does NOT like any moisture and does NOT like spoons dropped on it,, LOL - still a very pretty floor,,, oh well, live moves on

    Bookmark   June 16, 2013 at 12:20PM
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If you have below grade concrete floor, and get moisture vapor through concrete from below, don't you need to adhere the plastic film to the concrete so there is no air between the film and the concrete? Otherwise, the moisture vapor will condense between the plastic and the concrete, and you will have water, and even mold, and the concrete will degrade, turn dark. I've seen it. You can seal in the water and smell with tape, and the damage occurring to the concrete, but 10 years later, pull up the flooring, and there it is. I think that is why plastic sheet I adhered in an airtight way below grade damp environments, so water vapor won't condense under it. But let me know if this is incorrect.

    Bookmark   January 30, 2014 at 12:32PM
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