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Tiling bathroom, need help with subfloor

12 years ago

This will be my first time tiling. I just removed the old tile from the bathroom, it's probably been there for 50 years. Most of it was no longer adhering to the subfloor which was plywood. When we stepped on the tile in bare feet the tiles would stick and pop off the floor...lol. So it's time.

Joists are 16" on center. I'm new to this stuff so bear with me.

When I look at the floor there are the joists, then on top of the joists are 1" thick planks about 7" wide, then on top of that there is about 1/4" plywood and then the tile.

My original plan was to remove tile, then lay Ditra on top of the existing plywood, but the plywood looks nasty. it smells and there is still adhesive on it. I guess I could sand it down.

What are my other options? I could rip up the plywood and just lay another clean new sheet of plywood and use the Ditra on top of that?

I could rip up the plywood and lay 1/4" sheets of cement backerboard?

I guess I could also lay backerboard on top of the existing plywood?

I've included a pic, it's a view down onto the floor, you see the plywood and then the 'planks' I mentioned. I just want to be sure I have a good sturdy subfloor for my tile.

Thanks for any help

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Comments (6)

mash74
Original Author
12 years ago
Couple of corrections. The plywood is actually 5/8" thick.
And when I said it smelled it's not a moldy smell or anything and there are no signs of water damage. More like a pee smell because my two boys miss the toilet and as I said the tiles really aren't sticking to the plywood anymore.
If I could remove the adhesive can I just use the Ditra over the existing plywood?
Or do I need to bite the bullet and rip the plywood up?

Thanks again
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StoneTech
12 years ago
If you are using tile and not a natural stone, I would scrap the plywood and install 3/4" plywood with a face grade no lower than "C".....screw it down well. Now, install either a cement board like Durock or, if height is an issue, use Schluter's "Ditra" as a base for the tile. Either material needs to be "bedded" in thinset. The cement board needs to be screwed in as per Mfg recommendations. I like the Ditra....lighter, use a flat trowel to push it into a modified thinset bed like Versabond using a 1/4" trowel to spread it.

Fill the cavities with your flat trowel. The next day, tile away!
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I went through all of this. Mongoct and Bill V. are very helpful. Joist. you may or may not have the ridgidity to tile with stone. It requires a stiffer floor system than ceramic. Check the JohnBridge web site and look at their "deflectolator" to determine, roughly, your capacity. Subfloor. If you use cement board it has to be thinset inplace as well as screwed down. The thin set is not to glue in place but to fill voids that may flex and cause cracking of the tile system down the road. If you use plywood as the underlayment it needs to be screwed down on center every 6" not glued down. Ditra is a decoupleing membrain that goes down after your self leveling compound is installed. Check out my post on floor joist on the remodeling forum and here. There is a link to the remodeling forum that is very detailed and time consuming to read and interpret. I provide a link below. Check out Bill V's. post on frequently asked questions. bathroom tile FAQ's-bathrooms Check out Staceyneil's post on " Self-leveling compound & radiant heat: what I learned..." Mongoct has very detailed information throughout different posts. Here is a link that might be useful: Progress on floor prep for slate tile
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Also, I know we can't put down SLC over the glue that's on the slab currently. Frankly, I'm concerned about using SLC successfully anyhow - we have two doorways and two staircases to work around. Can we do something else to level the floor? It's not terribly uneven. What about installing cement board with thinset? We could use the Laticrete 254 Platinum (or whatever product you recommend) and level the floor with the thinset. Would that work? I don't think cement board is normally recommended for concrete floors, but if it's feasible I think it might be the best bet.
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what type and condition of wood is your joist in, and what is the unsupported span distance of your joists ? With those in combination with your other joist information you can calculate your floors deflection ratio (which needs to be within L/360 of the span for porcelain ceramic). Ditra is by far superior to hardibacker, however hardibacker should work fine. go with at least 3/4" of plywood.
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The Ardex 8+9 will handle that OK. I used a little mesh and thin-set as a double down approach on a couple cracks in this room myself. Not needed by the book but I thought it could not hurt. Level changes are the worst. These can be settling cracks and the settling can still be going on. Little cracks are common. These are the cracks I covered with some mesh and some thin-set. I let this dry out a few days before adding the Ardex 8+9 Crack Isolation over top. The spray foam was used to fill the gap under the drywall. Block Silver Fish from having a home. I cut it back so it was 1/2" high and a 1/2" wide. This will give me a compression zone later when I tile and prevent the tile from being installed two tight in this Sun Room.
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mash74
Original Author
12 years ago
Thanks for the reply StoneTech. Yes, height is definitely an issue which is why I was thinking of going with the Ditra.
So you think I should definitely scrap the existing 5/8" plywood?
I was hoping to avoid ripping it out and then buying/cutting new plywood but it does seem like it's going to be pretty tough to get the existing adhesive off of the plywood.
I think if I left any of that old adhesive the bond between the Ditra and the plywood could be bad.
Thanks for the input, I think I'll rip out the old plywood tomorrow.
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mash74
Original Author
12 years ago
Oh, and this is a ceramic tile.
Thanks
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mash74
Original Author
12 years ago
Another question regarding the plywood, while in Home Depot I saw that they have tongue in groove sheets. Is this better when laying tile? Or are the regular sheets better?
Thanks
0
StoneTech
12 years ago
The T&G is probably a bit better, but I would put them in tight and then pull them out about 1/8".....also set them perpendicular to the joists and stagger the rows. Don't let four pieces all meet together. (+)
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