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-   -   Gluing hardwood planks directly to slab? (https://www.johnbridge.com/vbulletin/showthread.php?t=129342)

makethatkerdistick 06-15-2020 04:39 PM

Gluing hardwood planks directly to slab?
Just learned that one of my colleagues is having hardwood floors installed directly to their slab on grade foundation. This just doesn't seem right to me, does it? I see no vapor retarder, just the bare slab (with some typical hairline cracks) onto which the installer is applying an adhesive with a notched trowel and then sticking the planks on top.

I thought a quality install would include vapor management and possible a subfloor/sleepers on top of a slab before the finished material goes on. Or am I wrong here? Just curious if this is an accepted practice.

cx 06-15-2020 09:48 PM

Glue-down nominal 3/4" hardwood over SOG has been accepted in this part of the country for years, Woolfgang. I was very, very skeptical the first time one of my customers asked me about it when she had contracted with a local flooring company to do such an installation in her house when it was probably 15 years old or so. Replacing bedroom carpet.

I talked with the flooring company on her behalf and they assured me that it was now an approved method according to the adhesive manufacturer, Bostik. I talked with Bostik and they assured me that they had had excellent success with such installations.

That particular job is still quite intact (maybe 10 years?) and I've seen it within the past year. Some problems with the wood finish, but not with the installation. I know of other such installations, but that's the one with which I'm most directly familiar. I've never done, nor had done, any such installations in any of my houses.

And I know that particular SOG to have a proper vapor barrier under the concrete.

jadnashua 06-15-2020 11:35 PM

Moisture can turn a hardwood into a pretzel. If that was covered when the SOG was poured and the SOG has dried out enough afterwards, it can work. Wouldn't want to do that over a green slab.

My preference is a floating floor over a cushioned vapor barrier, but clicking it together can take a bit longer depending on how familiar you are with it, and I think that slight cushion, even under a solid wood product can be felt versus gluing it down.

Tool Guy - Kg 06-15-2020 11:51 PM

Bostik’s Best has had a fantastic reputation for years and years and years for installing hardwood to slabs. Handles moisture and bonding in one product. Hopefully, this is the product they’re using to install the wood.


makethatkerdistick 06-16-2020 11:30 AM

Interesting. I suppose I learned something new then. I would assume their slab house has a proper vapor barrier between the soil and the concrete. The added benefit would then be to have no extra subfloor height to contend with. Given the overall dryish North Texas climate, I can then see how this would work.

When I bought my home I foolishly looked into hardwood floors. That was when I thought all my house needed was a coat of paint in the bedrooms and living room. I disabused myself of such flooring plans quickly once I learned about costly repairs that required my attention. Anyway, the guy who gave me a quote at the time suggested a subfloor with vapor barrier and sleepers. He was obviously doing it the traditional way. Too bad for him that I didn't have any money then (or now, for that matter).

Tool Guy - Kg 06-17-2020 08:54 PM


Originally Posted by makethatkerdistick
...I would assume their slab house has a proper vapor barrier between the soil and the concrete...

Absolute pot shot in the dark to whether that’s true in this case.

cx 06-17-2020 09:27 PM

What Goldstein said, Wolfgang. Not everyone does proper preparation for SOG foundations just like not everyone does proper preparation for ceramic tile installations as evidenced by the threads in our Advice forum.

I'd wanna do some serious MVER testing before I committed to such an installation. I don't recall what Bostik's limit is for that application.

I'd start with several patches of poly taped to the slab in various places that were to receive the hardwood installation. If there is any indication of moisture, I'd then want to do a proper calcium chloride test.

My opinion; worth price charged.

makethatkerdistick 06-18-2020 07:36 PM

The calcium chloride test is among my top ten favorite building tests. Only the lead test is more fun :D

I am not going to say anything and take away from their upgrade. Usually, people have disliked me for bringing awareness to possibly unpleasant things.

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