1) You should have a double layer of plywood beneath your tile substrate so yes, I would use the 1/4″ additional layer (1/2″ would be better). You do not need a moisture barrier on the floor of the bathroom. The marble and grout are not waterproof but the amount of moisture it will be exposed to should be minimal and will more than likely evaporate off the surface before enough is soaked in and retained to create any damage. And if not – I wanna party at your house.

2) Green board is fine – I hate it – but it’s fine. It’s just a personal thing and I’m a stubborn, bull-headed bastard. Kerdi will stick to it just fine.

3) No real need to seal it with anything, just use a good latex-based paint and it will be fine.

Is it just me or does it seem like I typed the word ‘fine’ excessively in this reply? By the way, the walls you tore out were mud walls – I still build them when I find someone willing to pay for them. They *really* last forever! No fun to tear out, though.

Give your dog my regards.

Yes, the layer of 3/4 and the 1/2″ CDX will be a suitable substrate for your ceramic. Be sure to install thinset beneath your cement board to fill any voids and ensure a solid layer for tile.

You can put the tub on top of the cement board or place the cement board up to the tub – entirely up to you. Either way is completely acceptable. If you place the tub on the plywood and put the cement board up to it be sure to leave about a 1/16″ or so gap between the tub and cement board. Many people butt it right up to the tub and eventually, due to movement of framing, joists – you know, regular stuff, the tub will move just enough against that edge of the cement board to give you a nice little squeak every time you step into the tub and it will drive you absolutely insane! (It does me, anyway )

The house is on pier & beam. I plan to tear the bathroom floor down to floor joists & would like to have ceramic tile in the bathroom.

Is one layer of 3/4 plywood nailed to joists, followed by 1/2″ CDX plywood NOT nailed to joists OK for a subfloor?…followed by 1/4 cement board on top of the 1/2″ plywood?

Since I am replacing the tub, is it OK to put the tub on top of the cement board or should cement board just be placed “up to the tub”–that is put tub on top of plywood?

Thank you again for an informative website!

Jeanie

Had 3 questions – 2 directly about tiling, and the 3′rd not-so-much, but given you’re experience thought you might have come across it..?

Its a ~50 year old home, fixer-upper, 2-story colonial-style (almost done, just the bathrooms left). Questions relate to the Master Suite, which is on the 2nd floor directly above the already remodeled kitchen). We’ve gutted the room, back to studs – was an old original (lemon-yellow tile, and leopard-skin wallpaper on top-half walls and ceiling – a real treasure) mortar/tile job (OMG what a back-breaking process that was). The original subfloor was 1/2-inch ply and what looked like tar-paper under the mesh. Completely rotted out, so cut it all away. Have sistered up various joists where either damaged, or required (putting new large soaking tub in). All Joists are 10X2 on 16-inch center. Replaced the subfloor with 3/4 inch ply to start with, and screwed it all down, now it feels nice and solid. My questions…

1. We’re installing small marble subway-tile (1/4 inch thick, 2X4 inch size, come on pre-mounted 12X12 mesh sheets) on the floor. I’m intending on following this article to the letter… [possibly further 1/4 sheet of ply - should i bother?], trowelled thinset, 1/2-inch hardibacker, then thinset and tile install. Do I need any sort of moisture barrier/plastic sheet etc? And if so, where should it go? Everywhere I’ve read, including here, it says ceramic or marble etc are NOT waterproof, and neither is the backer. The current 3/4 inch Ply subfloor is untreated. Do I have to stop any moisture from getting to the subfloor, or all the way through and into the kitchen ceiling below? (Just for clarity, im NOT talking about the shower box – Im using schluter shower system for that, with kerdi-lined shower box walls – just referring the rest of the room floor).

2. Im installing 1/2 inch green-back drywall on the walls in general. For the shower-box specifically, we’re putting Kerdi membrane on the walls, is it ok to use the same green-back drywall in rest of the room, as the shower backing behind the membrane (rather than just normal drywall as Schluter suggests?) Is the green better/worse? Membrane still stick ok? Or go hardibacker instead?

3. (and for the non-tiling question…) I was going to put the green-back on the ceiling too, but then found that for ceilings it requires closer joist-center distance than 16-inch, so opted not to, and will be forced to just put standard drywall on ceiling (1/2-inch still). Do we need to specially seal the ceiling drywall before painting? (especially above shower box?) Any ideas what with?

Sorry for the long post, and advice hugely appreciated.
Cheers.

I’m unsure who advised you to build a sleeper floor to tile over but that is one of the worst solutions. You’re absolutely correct, depending on the quality of wood used, the height, as well as several other factors the amount of movement makes it unsuitable for tile installation.

Your best option is likely another mud bed. Just tear out what needs to be gone and mix up some deck mud (just like a shower floor) and create yourself a nice flat, solid substrate for your floor. It’s cheaper and better and a proven method – no way to lose.

My question is about the sleeper floor. How sturdy is a sleeper floor…I mean it has space between my original subfloor and “new” higher floor. I am thinking that the tiles will crack over time.

The second question is how important is it to get the strips of wood parallel and attached to the floor joists on this sleeper floor? It seems that I would be redistributing the weight of my floor if the base of my sleeper floor is not over my floor joists correctly.

Thanks for any advice you can give me

And so I did a test run. I have some interior french doors that had warped jambs- got them at a steep discount. Of course, this was b/f I started studying & experimenting as a DIY’er & I did not realize the jambs were warped. Thanks for letting me ramble here. I figured if I can get those doors hanging properly, I’ll trust my abilities & attempt installing a front door. Well, success! The doors are hanging almost perfectly. (Can doors ever be perfect?) The reveals are pretty straight & the doors open & close smoothly. It took me three days, but I’m happy

So I am going ahead with the front door. Still some hurdles to cross. I really need a better math education- don’t tell my kids. I must crunch the numbers to make sure I can raise the door up enough. Not sure if I have enough clearance up on top. And the door jamb widths on the exterior pre-hungs at home depot & lowes are only about 4 & something wide. My door opening is around 8″. I know I may have to do a jamb extender.

Slow & steady here. Slow & steady.

The 3/4″ plywood beneath the threshold does not have to be tied into or a part of the actual 3/4″ of plywood beneath your tile in the entryway, it can be separate. The only purpose of placing it there is to give your door enough clearance. It does not necessarily need to be installed last. As long as you can get it moved up with enough clearance before you start that would work fine as well.

Problem is, if I take out the front door, I can’t leave the door off for a week. I need to get the new door up the same day. I don’t know if I can finish that fast.

So now I need to get a professional to install the door & only then can I continue with the tile.

Even with 3/4″ planks you need 3/4″ plywood. You do not need to use the 1/4″ backerboard, you can use something like Ditra which is only about 1/8″ thick. The purpose of the underlayment is to have a substrate suitable to stick the tile to. Backerboard, Ditra, things like that. The thickness is not important.

You can either take a look at the joists from below or take off the planks to get a look at the joists if you want to. Not really necessary unless you want an actual deflection number.

If you are going to install a new door I would pull everything out including the threshold, install the 3/4″ layer of plywood, replace your threshold and place the new door on top of the saddle at that point. That should give you enough clearance for your underlayment and tile.

Your not completely crazy… Just enough to want to install tile.