Posted: 11/29/2008 5:51:00 AM EDT
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I'm replacing the floor in a half bath. The old tile (circa 1968) was installed on a thick mud bed (which is now gone). Currently I have just the 1/2" plywood subfloor and need to figure out what sort of underlayment to use. Type of tile is still TBD, but probably either 12" marble or 4" tumbled marble.
Do I use 5/16" cement board over 3/8"? Should I just forget the extra plywood layer and use 5/8" cement board directly over the subfloor? Thanks for any help! |
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the easiest and cheapest thing to do is to lay down an 1-1/4 mud bed over the 1/2inch plywood, But if you are not up to the task (Most people are not up to the task)
, lay 3/4 plywood (Screw it down good) over the 1/2 inch then place 1/2 inch wonderboard on top (Follow the directions on the wonderboard). As stated by the previous poster large tiles require a solid backing. |
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Quoted:
Thanks for the input. I have a max of 1.25" to work with (on top of the current 1/2" subfloor) before the transition to the hallway gets unreasonable. How about another layer of 1/2" plywood, plus 1/4" Hardibacker, and then tile on top of that? I would not do it, I would go a Min. of the additional layer of 1/2" ply wood, But I would use the 1/2" backer. The 1/4" stuff is meant for use over sheetrock on walls, It is really Not for floor use & I do not think it will hold up. Don't worry about the transition, A little step up to the bathroom floor is not going to bother anyone. |
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I have always screwed down the 1/2" really good
glue 3/8 plywood making sure the joints are staggered on top with lots of liquid nails Staple it down with 3/4" narrow crown staples 2" along the edge and 4" every direction within the field Repeat the stapling and glue with 1/4" hardibacker with the joints also staggered mesh tape the joints and glue the mesh down with redgard which will hold the mesh down and help prevent cracking Install the tile with the best polymer modified thinset you can find I have been a general contractor for 12 years and never had a callback on a floor we have installed due to cracking 1/4 " is specifically designed for floors since height is a consideration 1/2 for unsupported walls that will flush up with drywall There is no reason to use 1/2" on the floor as it adds no strength to the install a good book on the subject is tiling with michael byrne by taunton press feel free to IM me with questions. |
| Ditra! Check your joists to see how far apart that they are and the span. Ditra will install on 3/4inch bc plywood. It would be best to have at least 1 inch sub floor and the proper span. Ditra is only about 1/8 inch and you can get it at home depot. Use latex mortar to adhere it to the subfloor and use non modified to install your tiles. |
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Quoted:
Ditra! Check your joists to see how far apart that they are and the span. Ditra will install on 3/4inch bc plywood. It would be best to have at least 1 inch sub floor and the proper span. Ditra is only about 1/8 inch and you can get it at home depot. Use latex mortar to adhere it to the subfloor and use non modified to install your tiles. Yup. A good non modified. the cheap stuff at Depot sucks, not enough portland in it. Mapei Kerabond is what I used. |
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Thanks for the advice everyone.
Original subfloor is 1/2" ply and I've added another layer of 1/2" ply over that. Joists are 2x10 and span about 11'. Spacing is generally 16" OC, but this bathroom has a doubled joist running right down the middle and another that's spaced at about 10". Room is only about 4.5' wide by 8' long with the joists running long-ways under the room. Currently looking in to using Ditra. Tile has been ordered––12" polished travertine; about 230 sq ft (going all the way up the walls). Vanity has been ordered too. My credit card hurts now. 
Here's a picture of midway through the demolition: 
And this is the vanity that's going in: 
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Goodness, have you done your floor yet? There is some really good info and some absolutely crap info.
Basically your finished floor will only be as good as the subfloor its laid upon. If you want to do it right you need to make sure the subfloors deflection is suitable for the finished floor. Natural stone is considerably heavier than ceramic or porcelin tile, not too mention a mud bed. You need to make sure there is no flexation along the length of the joist or with the plywood that spans between the joist. You could easily lay a floor that looks fantastic, only to fail later down the line. If the subfloor is suitable to carry the load, then you should go with a minimum of 3/4" ply, refer to HandyDave's post. If finished floor height is a concern use, 1/4" CBU or Ditra which is only 1/8" and also helps by acting as an uncoupling membrane that allows the tile floor to move independant of the subfloor. In any event, if you have further questions, I would suggest John Bridge Forums |
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I have not done the floor yet. I think the structure should be stiff enough to support the tile. Joists throughout the house are generally spaced 16" o.c. but they are closer under this bathroom (one doubled joist in the middle, and all but one of the other spans are less than 16"). I'm adding a few cross braces between joists just because I can. The "deflect-o-lator" over on the John Bridge site says I'm ok for stone when I use a rough average of my slightly irregular joist spacing.
I'm following handydave's advice and using another layer of 1/2" ply over the existing 1/2" subfloor (except screwed rather than stapled). Still debating on Ditra versus 1/4" cement board on the floor. Nothing's going to happen with this project until after Christmas. This is my first major tile project...hopefully I don't screw it up! |
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Dry cut all the wonder board pieces to fit bathroom, then mud floor with flexbond from homedepot with a 1/4" notch trowel, then install wonder board pieces, then while still wet screw down wonderboard to wood putting a screw every 6".
do it this way and it will be solid as a rock and its not coming up forget dirta, save your money, ive been doing bathrooms and floors for 15yrs check out my site BathsAndFloors.com |