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Thread: Subfloor build up order?

  1. #1
    DIY Member ironspider's Avatar
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    Question Subfloor build up order?

    First off all thanks to everyone that helped me out in my previous post! I found that deflection calculator which was a great tool and helped me to understand that I think I will be going with ceramic tile instead of slate for our bathroom remodel.

    Okay, back to the NEW post here! Basically we tore up our first floor bathroom because it was *extremely* dated and we wanted to put in a different tub/vanity/mirror/faucets/toilet etc. . . So we finially finished the demo and now we are in the reconstruction phase.

    Our new goal will be to go with cermaic flooring tiles. So what I need to determine is what we need to do to the floor to get to the tiling stage.

    After removing the old "mud floated" floor we now have a subfloor of 1x6 wooden planks. I replaced several that had cracked or had gotten hit by water so the subfloor looks "good" but obviously--it has spaces in it so we can't put any sort of thinset mortar or anything on it (duh!).

    So, given a 1x6 plank subfloor in good shape and the ultimate goal of ceramic floor tile what materials will I need to use to get us to the tiling stage?

    I would think that it would be something like this (but I don't know the thicknesses which is another issue I need resolved):

    1. 1x6 Plank subfloor (already in place)
    2. plywood/osb?
    3. Some sort of leveling compund? (any brand recomendations)?
    4. thinset mortar layer?
    5. Cement Backerboard (like HardieBacker?)?
    6. thinset mortar layer?
    7. Tiles?

    So is that the correct order? and what thickness of materials will I need to use? And, most importantly, what the heck am I missing?

    Thanks!

  2. #2
    One who lurks Basement_Lurker's Avatar
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    1. get rid of that 1x6
    2. put down 2 layers of T&G fir plywood, two 5/8" sheets would give you min specs, but two 3/4" would be better.
    3. use SLC if necessary, although it shouldn't be.
    4. put down a layer of ditra if the budget allows for it
    5. set your tiles

    You should spend a week perusing johnbridge.com before attempting this project at all or asking follow up questions.
    Last edited by Basement_Lurker; 01-01-2009 at 09:46 PM.
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  3. #3
    Plumber jimbo's Avatar
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    Unless you are way out of whack , you would not need leveling compound.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You need a minimum of 1/2" ply with exposure I glue (almost all is this, but check) that has C or better faces on both sides on top of the planks. Then you need a decoupling layer; 1/4" cbu is fine (Hardibacker is one brand), or you could use a membrane like Ditra (www.schluter.com) which I prefer since it is light and easy to install, and works better (uses more thinset, though).

    You should ensure the planks are well anchored to the joists...use screws if necessary to anchor it well. Don't anchor the ply to the joists, but to the planks - this provides more decoupling.

    Ensure you use the thinset under the cbu if you go that route and offset the seams so you never have four corners together or over a seam in the ply. You will also need to use the alkalai resistant mesh tape (looks like but is not the same as used for drywall) on the seams. It is easiest to install this while tiling to avoid speed bumps. You aren't finishing drywall, you are just embedding the tape over the seams to help make it monolithic - looks isn't important.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Member ironspider's Avatar
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    Jim,

    I just watched a youtube video on that Ditra system and that looks very cool. Too bad no one makes ceramic floor tiles that look that cool

    Anyway, so, let me see if I am reading you correctly here and if this would work:

    1. Put down 1/2" or 3/4" (3/4" preferably) plywood made with Exposure 1 Glue that has C or better faces on both sides.
    2. Attach this plywood to the existing 1x6 planks using decking screws running about 8" off the joist
    3. Lay down my thinset and ditra as shown in the Ditra instructional video
    4. more thinest on top of Ditra
    5. Tile

    Does that look about right?

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    That should work if the joist deflection is at least L/360. If you have trouble finding Ditra locally, you can order it on-line through the store on www.johnbridge.com. HD in some areas carries it in smaller rolls (smaller rolls retail are more expensive than larger rolls - check the prices on the Tile-your-world store as shipping may or may not make it less expensive - usually does).

    If your floor is very uneven or not level, there are ways to fix it, but tile needs flat, not level, but level is nice, too.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    DIY Member ironspider's Avatar
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    Quote Originally Posted by jadnashua View Post
    That should work if the joist deflection is at least L/360. If you have trouble finding Ditra locally, you can order it on-line through the store on www.johnbridge.com. HD in some areas carries it in smaller rolls (smaller rolls retail are more expensive than larger rolls - check the prices on the Tile-your-world store as shipping may or may not make it less expensive - usually does).

    If your floor is very uneven or not level, there are ways to fix it, but tile needs flat, not level, but level is nice, too.
    Thanks Jim,

    I have calculated the deflection at L/505 using the John Bridge calculator.

    Thanks for the tip on where to order Ditra--if my HD doesn't have it I'll ordr it through there.

    Last question I have is that our bathroom is coming out almost *exactly* at 8x8 which, obviously, would mean buying 2 4x8 sheets of the 3/4 plywood to screw onto the existing planks. My wife's car is a hatchback but in the past we tried to transport a 4x8 sheet and it wouldn't fit. HD will cut wood for you for free (first cut) so would we be hurting our floor rigidity/deflection by having them cut those 2 sheets in half so we can fit them into the hatch?

    In order words, will I notice any difference if I put down 4 pieces of plywood (4 2x8 strips) instead of 2 pieces of plywood (2 4x8s)?

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    Probably not, but you'd be better off with them whole. Some padding and rope if you don't have to go too far and keep your speed down should get them home intact...or bug a buddy with a bigger vehicle.

    When using Ditra, you'll need a modified thinset to adhere it to the plywood, and then must use an unmodified above it. HD doesn't sell a decent unmodified thinset (although they have some fine modified ones). If you want to only buy one type, you can check out Lowes to see if they sell Mapai and get their dryset and some modifier addative...use it with the addative for under, and without for above the Ditra. A really good unmodified, you may be able to get at a tile store, is Ditra-Set. Schluter has it made for them to their specs and it is a really nice, creamy thinset that is easy to work with; and, it doesn't cost an arm and a leg, either. You can download the Ditra installation manual at www.schluter.com. It's pretty comprehensive about subfloor prep and installation of their products. Follow that, and they'll warrantee the installation.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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