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Anyone Tapcon Ply Subfloors into Concrete? Screw Spacing?

FinishedBasementGuy | Posted in Construction Techniques on February 7, 2022 12:18pm
What is an appropriate screw pattern for affixing 4×8 panels to concrete? All the info I can find online refers to screwing ply to wooden joists, etc.- not to concrete. 

The context:
I’ve got a “basement” room in a slab on grade bi-level house with partially below grade lower level.

– Pulled up 50yr old carpet, down to the concrete. 
– Put concrete sealer across the exposed 11″x11″ area.
– Underlayment of DMX 1-step 2.0 dimpled plastic.
Now, I’m adding 3/4″ T&G Advantech 4×8 subfloor panels.

Using 1/4″ tapcons, fastening the panels into the concrete (thru the underlayment, of course).


I’ve seen recommendations for 6″-8″ spacing around the perimeter, starting 2″ in from panel’s edge. Also seen 12″, 19″ rec’d spacing. 
 
Seems like a lot of the recommendations are for applications over wood- so I’m wondering if applications over/into concrete are different.
 
Has anyone else screwed ply into concrete through an underlayment? What sort of screw pattern did you use?
Reply

Replies

  1. catmandeux | Feb 07, 2022 04:31pm | #1

    DMX 1 Step is intended as an underlayment for a finish floor directly over concrete.
    Why the subfloor?
    I expect driving screws through the DMX will defeat the waterproof barrier.

    1. FinishedBasementGuy | Feb 08, 2022 06:59am | #4

      Thanks and yes- I've seen installers seal the drill holes with silicone before driving the screw, to maintain the barrier. I'll do the same.
      Still, I need to confirm how many/what spacing of screws are needed. Any help on this?

      1. catmandeux | Feb 08, 2022 03:01pm | #8

        Install requirements from other vendors of similar products:
        Platon: Screws are 24" grid pattern https://www.spycor.com/v/vspfiles/templates/1/assets/Platon%20Subfloor%20Product%20Brochure.pdf
        Delta-FL: 8 screws per panel, staggered pattern: https://www.dorken.com/media/docs/products/Installation-Guides/Installation-Instructions_DELTA-FL.pdf

        You may want to check with the DMX support folks for their recommendation.

  2. kayakmsdt | Feb 07, 2022 04:33pm | #2

    Try looking at Rawl anchors. You drill through the material, into the concrete, and nail the anchor like a construction nail. I use them exclusively to anchor my bottom wall plates when constructing walls. They might work for plywood. And they will not pull out! https://www.fastenal.com/product/details/50610

    1. FinishedBasementGuy | Feb 08, 2022 07:02am | #5

      Interesting- thx. What do you use to nail them?

  3. calvin | Feb 07, 2022 11:32pm | #3

    I’ve tapcon’d a lot of things to concrete.
    I would certainly try my Hilti P.A.D. gun b/4 my arms gave out.

    Have you thought of dbl layering floating ply?

  4. FinishedBasementGuy | Feb 08, 2022 07:03am | #6

    Would love to dbl floating ply- don't have the room in my floor height- resulting floor would be too tall.

    Still, I need to confirm how many/what spacing of screws are needed. Any help on this?

    1. kayakmsdt | Feb 08, 2022 09:03am | #7

      Depending on the thickness, 6-8" spacing would be secure.

  5. andy_engel | Feb 09, 2022 06:10am | #9

    Just do a double layer of plywood and skip the concrete fasteners.

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