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Bathroom Subfloor Questions for Ceramic TIle

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  • #31

    Re: Bathroom Subfloor Questions for Ceramic TIle

    Originally posted by altiplano View Post
    I'd do a second layer of 5/8" ply, LOTS of screws, and ditra.

    Make sure you use the correct trowel size and mortar putting down the ditra and tile.

    Good luck.
    A specific 4" at teh edge, 6" in field screw pattern is what the John Bridge Forum guys most often recommend IIRC.

    And yes, trowel notch AND type of mortar for Ditra is VERY important. Last I read you needed Unmodified Thinset mortar under the Ditra, and not to use Modified Thinset (Thinset with polymer glues and compunds added).

    Mapei KeraBond Unmodified Thinset is what I've always used under Ditra and Kerdi. Available at Rona and Lowes. When mixing the thinset, stay very close to the instruction times for the initial mix, slake/rest time, and the second mix. There's some good youtube videos on how to properly mix mortar for Ditra in order to get just teh right water/moisture content to ensure the fleece backing on the ditra/kerdi bonds correctly.

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    • #32

      Re: Bathroom Subfloor Questions for Ceramic TIle

      Originally posted by cstephens2 View Post

      A specific 4" at teh edge, 6" in field screw pattern is what the John Bridge Forum guys most often recommend IIRC.

      And yes, trowel notch AND type of mortar for Ditra is VERY important. Last I read you needed Unmodified Thinset mortar under the Ditra, and not to use Modified Thinset (Thinset with polymer glues and compunds added).

      Mapei KeraBond Unmodified Thinset is what I've always used under Ditra and Kerdi. Available at Rona and Lowes. When mixing the thinset, stay very close to the instruction times for the initial mix, slake/rest time, and the second mix. There's some good youtube videos on how to properly mix mortar for Ditra in order to get just teh right water/moisture content to ensure the fleece backing on the ditra/kerdi bonds correctly.
      Absolutely, John Bridge is a very good resource with many helpful posters... and yeah that spacing is correct. It's a lot of screws for putting down the ply. But if you are investing the time and money, you might as well do it right.

      I believe the Ditra trowel is a 4.5mm or there's a bigger size recommended for Ditra XL. Rubi tools makes one.

      There are many suitable thinsets out there, I've used the Tec 337 unmodified thinset which used to be labeled as for Ditra, but now just labeled as for uncoupling membranes as I believe Shluter now sells their own mortar. It's available at Centura. If you are unsure based on the Schluter data and what's available in your area, I'd call Shluter to confirm.

      Schluter has a lot of info available on how to use their products, I've called them with questions in the past also and they're very knowledgeable and helpful to deal with.


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      • #33

        Re: Bathroom Subfloor Questions for Ceramic TIle

        Originally posted by altiplano View Post

        Absolutely, John Bridge is a very good resource with many helpful posters... and yeah that spacing is correct. It's a lot of screws for putting down the ply. But if you are investing the time and money, you might as well do it right.

        I believe the Ditra trowel is a 4.5mm or there's a bigger size recommended for Ditra XL. Rubi tools makes one.

        There are many suitable thinsets out there, I've used the Tec 337 unmodified thinset which used to be labeled as for Ditra, but now just labeled as for uncoupling membranes as I believe Shluter now sells their own mortar. It's available at Centura. If you are unsure based on the Schluter data and what's available in your area, I'd call Shluter to confirm.

        Schluter has a lot of info available on how to use their products, I've called them with questions in the past also and they're very knowledgeable and helpful to deal with.

        Schluter has been great to call and ask questions.

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        • #34

          Re: Bathroom Subfloor Questions for Ceramic TIle

          Originally posted by cstephens2 View Post

          Thatched roofs are indeed neat, and I been in buildings in the UK with thatched roofs and spoken to the owners about the upkeep and maintenance of them.

          Thatched roofs are *not* allowed for any new construction in the UK and are only maintained on buildings for historical purposes from what I was told while I was there (early 2000's). There was also significant retrofitting of fire suppression systems into the buildings I saw (sprinklers) to deal with the ever present additional fire hazard. Its possible that new installation approaches with some sort of fireproofing applied to the thatch has changed this.

          So yes, once upon a time a valid building practice (in the UK at least) that has been made obsolete with modern engineering and materials science for various reasons (cost, comfort, safety, longgevity, etc).
          And seems to be popular and upcoming in Europe.

          Egon
          from
          The South Shore, Nova Scotia

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          • #35

            Re: Bathroom Subfloor Questions for Ceramic TIle

            Originally posted by cstephens2 View Post

            The addition of 1/2 or 5/8 play would definitely be beneficial for torsional support, but beam/joist deflection is measured independently of floor sheeting. Cross or solid blocking between beams/joists DOES improve beam deflection to a degree.

            And yes, additional support posts would change the length of the 'span'. 'Span' is the unsupported distance between support posts or load bearing walls. Reading the OP's first post, his numbers seem to be measurements of unsupported span, but thats an assumption on my part. If indeed OP's measurement is ~12.5' unsupported span with a 2x8 joist, his deflection is approximately L/270.

            Simply put, a 2x8 with live loads on a span of 12.5 or more feet has too much deflection to install Ceramic or Porcelain and have the install last based on my past readings and moderate DIY experience.

            As I posted in my original comment, the OP should really head over to the John Bridge Forums and ask his question there. The forum participants will often ask for pics or make clarifying questions to get as good an idea as they can to help. They answer questions exactly like OP's every day and the forum is filled with tiling professionals.
            A simple span based on end supports with full rotation is in a different word than the real situation.
            Egon
            from
            The South Shore, Nova Scotia

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            • #36

              Re: Bathroom Subfloor Questions for Ceramic TIle

              Originally posted by Egon View Post

              A simple span based on end supports with full rotation is in a different word than the real situation.
              You havent asked OP for a clarification. So....

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              • #37

                Re: Bathroom Subfloor Questions for Ceramic TIle

                Originally posted by cstephens2 View Post

                You havent asked OP for a clarification. So....
                So what needs clarification?

                Last edited by Egon; 11-18-2020, 01:49 PM.
                Egon
                from
                The South Shore, Nova Scotia

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                • #38

                  Re: Bathroom Subfloor Questions for Ceramic TIle

                  Originally posted by Egon View Post

                  So what needs clarification?
                  Nothing I guess. Get your last word in.

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