Solid Hardwood Options for Concrete Slab

Discussion in 'Solid and Engineered Hardwood Q&A' started by otterslide, Jun 15, 2019.

  1. otterslide

    otterslide Well-Known Member

    What thickness of solid hardwood and install methods are available for a concrete slab?
    I've only done flooring over 3/4" OSB, so I'm wondering what choices I will have if I have a concrete slab house.
    Also, if I am pouring the slab, how long do I have to wait before installing the wood? I am guessing I'd need to seal it first?

    Are straps the best way to keep everything tight? Once you strap an area, how long do you have to wait until you can continue?.. Sometimes I noticed that squeezing hardwood together causes it to push upwards, does this typically happen when using straps and glue down?

    If the wood is really straight and joins tightly and nice, I would think glue down is not too bad although never tried it, but if the wood has any issues, seems like glue down will be terrible.. is this the case?.. Or do straps work to close the gaps even if the wood isn't perfectly straight?
    I like the boards to have no space in between.. On my 3/4" nail down solid install over OSB I managed to get a really good result.

    I would prefer solid over concrete, but maybe I'd consider engineered floating as well, since it's probably a lot easier..
    I like Bona adhesives, so I'd be looking at using Bona for glue down.

    Thanks.
     
    Last edited: Jun 15, 2019
  2. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

    You have about 15 questions there on this thread. I think about 60 days on concrete to dry although a test or two would happen before. Generally, start straight and tap together on engineered. Doing one now that I clamp the first 4 rows til the glue in the joints sets, Shaw flooring glue sets pretty fast.
     
  3. Daris Mulkin

    Daris Mulkin The One and Only Charter Member I Support TFP Senior Member

    I was always told drying time on concrete was 30 days per inch thickness, and that was for carpet. Wood would be affected more from moisture so definitely do testing.

    :old:

    Daris
     
  4. Dan Schultz

    Dan Schultz Certified Wood Floor Inspector Charter Member

    • Like Like x 1
  5. Dan Schultz

    Dan Schultz Certified Wood Floor Inspector Charter Member

    Solid over concrete is doable.

    I like the method of covering the slab with 8 mil plastic allowing the plastic to go up the walls, overlapping and taping the seams.Running the plastic up the walls a bit allows it to be trimmed off behind the moldings.

    Then add two layers of 1/2" plywood, with the second layer installed on a 45° angle and fastened together. The top layer installed on a 45° will help the plywood stay flat. It also helps to prevent panelization gaps. Ensure to use fasteners that will not penetrate the bottom layer and puncture the plastic sheeting.

    Then you are ready to install your wood flooring. Again, make sure to use 1.5" maximum length fasteners so you don't puncture your plastic sheeting.
     
  6. Daris Mulkin

    Daris Mulkin The One and Only Charter Member I Support TFP Senior Member

    Dan, if he/she is using 2 layers of 1/2" plywood a 1 1/2" screw or fastener will penetrate the plywood by a 1/2". Might want to rethink that. Just saying.

    :old:

    Daris.
     
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  7. Mike Antonetti

    Mike Antonetti Senior Member

    Add the hardwood 7/16? And the angle of the fastener, (staple or cleat)
     
  8. Jim McClain

    Jim McClain Owner/Founder Administrator

    I don't think @Dan Schultz was referring to the plywood fasteners. Those would have to be coarse threaded screws with a maximum length of 1". Most commonly available 1" screw like that is for sheetrock, but I don't think it has the strength to withstand the normal movement in the plywood (I could be wrong). If it were me, I would make the bottom layer (if not both) 5/8" instead of half-inch, just to make sure I didn't have a problem if I drive 1" screws in too deep.
     
  9. Mike Antonetti

    Mike Antonetti Senior Member

    I currently have a few snapped drywall screws in som cabinetry I was trying to pull together, also going to replace my shed roof from OSB to plywood and want a screw that will not snap. So I got my ears on for recs.
     
  10. Dan Schultz

    Dan Schultz Certified Wood Floor Inspector Charter Member

    By the time you add the bottom 0.450" of the hardwood (top of the tongue) and drive the fastener at a 45° angle, it's all good.
     
    • Agree Agree x 1
  11. Daris Mulkin

    Daris Mulkin The One and Only Charter Member I Support TFP Senior Member

    Sorry wasn't thinking the angle and the thickness of the wood.

    :old:

    Daris
     
  12. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

    So the cleat or staple hold the wood floor on top is also attaching the 2 layers of plywood under it.
     
  13. phil verre

    phil verre I Support TFP

    I have floated plywood just like Dan says and had great results. I believe NWFA says 2 layers of 3/8" is acceptable? I also used urethane adhesive in between the panels. Make sure to leave 1/8" expansion gap between panels and 3/4" at all vertical surfaces. If i remember correctly NWFA says to use Black Poly?
     
  14. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    I wanted to add something to what Daris said about moisture in concrete because I hear that rule of thumb used a lot and it is an accurate statement it's just not the entire rule...

    The rule of thumb is 30 days per inch thickness...BUT per the conditions in the ASTM standards, the clock doesn't start until the building envelope is sealed and the HVAC is on and the building is stabilized at normal operating conditions. You can't even do a moisture test - either Calcium Chloride or Rh until those conditions are met. That's the rest of the rule that most people never heard of until they have a problem. :)

    The reason for this is because concrete can re-absorb moisture from the atmosphere above. If the internal Rh in the slab drops below the ambient Rh above the slab then the slab starts absorbing moisture - assuming it's a normal porous slab. How much and to what extent depends on how much troweling occurred and the types of sealers that were used. So you cannot count on getting consistency in the drying/curing curve until the building envelope is sealed and HVAC is on.

    Perfect example is the weather we're having this spring/summer here in the Midwest. We get a few days of warm dry weather and then we get a week of rain. Our Rh has been running very high and causing delays because nothings drying out the way it should be. You'd swear we were in Seattle. Great conditions if you're a duck.
     
    • Agree Agree x 2
    • Informative Informative x 1
  15. Daris Mulkin

    Daris Mulkin The One and Only Charter Member I Support TFP Senior Member

    Thank you CFR for that info. I did not know that, I just always heard and taught 30 day per inch. My stepson is a commercial installer and is having some slow times because of the moisture. Again Thanks.

    :old:

    Daris
     
  16. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    Daris, glad I could give back something for all you've taught me through your posts over the years!

    Yeah, I'm pretty sure I'm starting to grow webs between my toes. I look at the calendar and think that summer is here and then I look outside and it's still like spring. Heck, we had fog this morning - in the middle of June. Never seen anything quite like it. The farmers are tying life jackets around their seeds. The saying for corn is typically "knee high by the 4th of July." At the rate we're going they'll be lucky to plant by the 4th of July.
     
    • Agree Agree x 1
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