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  • Subfloor replacement in bathrooms

    I'm not sure if this should be asked here or in the plumbing forum. I am remodeling my 2nd floor bathrooms which are back to back. There was some dryrot and bad ABS dwv. The original floor is 3/4" OSB on 2x10 joist, 16 OC. I removed sections of the bad OSB which extended into bedrooms adjoining the bathrooms. Also replaced sections of sole plates. I replaced with 3/4" plywood T&G, glued (PL400) and ringshanked according to plywood manufacturer recommendations. The floor seems quite stury and I will be tiling the flooring in both bathrooms.

    Now my concern is about the hole I will make for the toilet in one of the bathrooms. The spot where I have to cut a 4 1/2" hole is exactly where a t&g joint is located. Is the t&g joint, which is glued, strong enough to prevent deflection? I will be going over the subfloor with 3/8" plywood before tiling.

    I also put blocking 2 x 10 between the joists at each point where the plywood meets the OSB.

    Thanks.
    Rick

  • #2
    Re: Subfloor replacement in bathrooms

    Drill.

    J.C.

    Comment


    • #3
      Re: Subfloor replacement in bathrooms

      If you wanted to flat block between the joist 2X4 or 6 on each side of the closet bend it couldn't hurt.

      Even without it the 3/8" is going to make it something to forget about.

      Comment


      • #4
        Re: Subfloor replacement in bathrooms

        Originally posted by JCsPlumbing View Post
        Drill.

        J.C.
        Hayngh?

        Mi no Sabi

        Comment


        • #5
          Re: Subfloor replacement in bathrooms

          Originally posted by drtyhands View Post
          Hayngh?

          Mi no Sabi
          No good?

          J.C.

          Comment


          • #6
            Re: Subfloor replacement in bathrooms

            Rick15752 wrote: "Subfloor replacement in bathrooms

            I'm not sure if this should be asked here or in the plumbing forum. I am remodeling my 2nd floor bathrooms which are back to back. There was some dryrot and bad ABS dwv. The original floor is 3/4" OSB on 2x10 joist, 16 OC. I removed sections of the bad OSB which extended into bedrooms adjoining the bathrooms. Also replaced sections of sole plates. I replaced with 3/4" plywood T&G, glued (PL400) and ringshanked according to plywood manufacturer recommendations. The floor seems quite stury and I will be tiling the flooring in both bathrooms.

            Now my concern is about the hole I will make for the toilet in one of the bathrooms. The spot where I have to cut a 4 1/2" hole is exactly where a t&g joint is located. Is the t&g joint, which is glued, strong enough to prevent deflection? I will be going over the subfloor with 3/8" plywood before tiling.

            I also put blocking 2 x 10 between the joists at each point where the plywood meets the OSB. Thanks, Rick"
            Rick,

            After cutting the hole for the toilet, cut some 2x6 or 2x8 blocks to go in between the floor joists. Place them in front and behind the drain pipe and as close to the drain as possible.

            Run a bead of const. adhesive on the tops of each (this will help hold them in place), put 2 screws through the sub-floor into the tops of the blocks, then reach through the hole and place 2 screws (toenailed), per end, into the joists. This will help increase the strength of the toilet, especially with the weight of the tile on the floor.

            Also, I wouldn't use 3/8" plywood over the 3/4" sub-floor. It is better to use tile underlayment such as ProVa Mat, Ditra, Unimat Pro, or Durock. ProVa Mat is what my tile guy uses with great success. It is available at most home improvement stores. Make sure you get the proper thinset for this product and use the correct trowel to lay it.

            Hope this helps?!

            Here is a pic:
            Attached Files
            Last edited by CARPENTERDON; 04-15-2010, 10:16 PM.
            Dimensional Carpentry & Custom Woodworking
            Historic Renovations, Restoration, & Custom Log Homes


            I Beat The Competition Hammersdown!

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            • #7
              Re: Subfloor replacement in bathrooms

              Thanks to everyone who took the time to reply. I was thinking of some extra blocking around the toilet to reinforce that area and you helped me make up my mind.

              Also, I will check out the tile underlayment recommended. I was going to use Ditra over the 3/8" ply. The 3/8" plywood was suggested when I visited the John Bridge Tile Forum. Originally, these bathrooms had particle board underlayment on top of the OSB. I think the PB was 3/8" or 7/16" (if they make that). My reason to place 3/8" PB over the 3/4" ply was to even out the floor incase some of the new subfloor was not even with the OSB.

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              • #8
                Re: Subfloor replacement in bathrooms

                Rick15752 wrote: ". . .I will check out the tile underlayment recommended. I was going to use Ditra over the 3/8" ply. The 3/8" plywood was suggested when I visited the John Bridge Tile Forum. Originally, these bathrooms had particle board underlayment on top of the OSB. I think the PB was 3/8" or 7/16" (if they make that). My reason to place 3/8" PB over the 3/4" ply was to even out the floor incase some of the new subfloor was not even with the OSB."
                Rick,

                When I lay tile, I use 1/8" luaun over the sub-floor, over that I use a self-leveling compound. After self-leveling sets up, I place a layer of modified thinset, next lay the waterproof membrane into the mod. thinset. When mod. thin. & membrane sets up, last step; lay the final layer of thinset and tile.

                Been doing it for many years (although not always with waterproof membrane) with great results. The membrane adds an extra layer of assured protection.
                Last edited by CARPENTERDON; 04-15-2010, 10:17 PM.
                Dimensional Carpentry & Custom Woodworking
                Historic Renovations, Restoration, & Custom Log Homes


                I Beat The Competition Hammersdown!

                Comment


                • #9
                  Re: Subfloor replacement in bathrooms

                  sigh.....NEVER EVER Luaun under tile no mater how you try and seal it with thinset it will delaminate deteriorate and cause cracks. seriously 35 years experience ?

                  Durock either 1/2 inch or 1/4 inch whichever works best for your finished floor height.

                  You thinset the durock to the plywood and screw with durock screws floor will come our as if it were a mud job.

                  Comment


                  • #10
                    Re: Subfloor replacement in bathrooms

                    Arthur96 wrote: "sigh.....NEVER EVER Luaun under tile no mater how you try and seal it with thinset it will delaminate deteriorate and cause cracks. seriously 35 years experience ?

                    Durock either 1/2 inch or 1/4 inch whichever works best for your finished floor height.

                    You thinset the durock to the plywood and screw with durock screws floor will come our as if it were a mud job."
                    I don't know what type of floors you have in NH, but it works here and there is NO de-lamination of the luaun, never has been.

                    I have tile in my own house done this way, been there for 17 years, still solid as a rock. I learned this method, 25 years ago from and old world Italian tile setter.

                    Durock, Hardiboard, and the like, are great products, especially in wet area application, but the luaun method has been used since before Durock, Hardiboard were ever invented. The luaun acts as a release between the sub-floor and tile. Luaun is very stable in this application and works very well.

                    So, before you start trying to dis-credit another contractors methods, you might look into the validity of that method. Personally, I think you like to S.U.S.!
                    Dimensional Carpentry & Custom Woodworking
                    Historic Renovations, Restoration, & Custom Log Homes


                    I Beat The Competition Hammersdown!

                    Comment


                    • #11
                      Re: Subfloor replacement in bathrooms

                      point old Italian tile setter before durock and i've done it myself (before durock and a few other products before even that)

                      in almost ALL cases the luaun has failed miserably the glue used to make it is NOT water resistand and the wood rots easily so when you use thinset to glue it down and on top the water from the thinset starts to rot it right away.

                      I've ripped up way too many floors with luaun as an underlayment and 99.9% of them it was the luaun that was trashed and caused the finished floor to fail. I wont even use it for vinyl anymore either.

                      Curious where you get 1/8th in luaun? i only have ever seen 1/4 sold in stores. 1/8th sounds like a door skin to me.

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                      • #12
                        Re: Subfloor replacement in bathrooms

                        I don't put thinset right on top of the luaun. I first use a leveling compound. The leveling compound not only levels the floor, but it seals the luaun as well. Then the thinset goes on top of the leveling compound.

                        Never have I had a problem!
                        Dimensional Carpentry & Custom Woodworking
                        Historic Renovations, Restoration, & Custom Log Homes


                        I Beat The Competition Hammersdown!

                        Comment


                        • #13
                          Re: Subfloor replacement in bathrooms

                          Rick, did you check your floor deflection? The tile industry recommends the L/360 criteria for tile floors and L/720 for natural stone, as bare minimums.

                          The John Bridge site has an app called "deflecto" that will calculate your floor stiffness for several (not all) types of floor construction.

                          I am surprised that you got a recommendation to go with 3/8 from that group. I don't recall any of the "real" guys over there ever recommending less than 1/2" ply. 3/8 ply will measure out at something like 0.330 - 0.340 thick. I can't imagine that's going to be good for much!

                          Personally I think you should *always* overkill the floor stiffness, especially if planning larger tile or if it's a room where you will have heavy furniture (or kitchen cabinets or a clawfoot tub ) on the floor. Unless you have a real serious stackup limitation, I would go with at least 1/2 ply... although as I said I prefer to overkill it and seldom use less than 3/4. Any interior grade ply has no business on floor job, IMO. Put a vapor barrier down before you set your plywood - 6 mil poly or 15# paper.

                          Then, as Arthur96 said, use some type of cement board - the 1/4 is fine for a floor. Again, if it was me and I could afford the stackup height of 1/2 Cement board, I would put thicker plywood down and go with the 1/4 cement board. The cement board adds no structure to the floor, it's just the underlayment. Agree also with Arthur about thinsetting the cement board to the plywood, and use backer board screws. You should not try to get away without thinsetting it. Screws are the way to go, but I have seen people successfully use ring shank nails. I like screws.

                          My favorite cement board is Wonderboard, but they'll all do the job. Hardibacker is a nice product but costs more and I don't see it giving a better result in the end.

                          I personally think Ditra is way, way oversold. If you get a good stiff floor and properly installed cement board underlayment, you won't need it. The stuff has its place to be sure. But it's being pushed for a lot of installations where it just isn't needed. Have you priced it yet? Yikes!! I would prefer to make the floor rock solid and pass on the Ditra but then again, it's your floor not mine. If your floor is flexy and you have large format tiles you're likely to have problems Ditra or no Ditra.

                          Good luck!
                          Last edited by Andy_M; 04-25-2010, 02:23 AM.

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