proper order of steps before laying tile?

[xoffers]

Hi, This is my first post, great site! After reading and learning quite from the pros I'm still in need of advice. I'm in the process of preparing the subfloor in my bathroom for tileing. The subfloor consists of 2 sheets of 3/4" ply with an 11/32" sheet of ply on top. The original floor was glued down linoleum so the 11/32" has old glue all over it but it's pretty smooth.

The floor is not level so my plan is to level it out and then put some 1/4" backer board down, then tile. Is this the right way to do it, can I put the leveling compound on the plywood with the glue on it or should I do the backerboard first? There are some low spots from different pieces ( thicknesses) of ply being spliced in from previous owner to fix water damage so I will still need to patch them before putting either ply or backer down regardless. Please don't tell me I need to sand the entire floor!

Thanks from Vermont!

[Kman]

Do I understand correctly that you have two layers of 3/4" ply and one 3/8"?

If so, I would probably try to remove the 3/8" for a couple of reasons. For one, if the 3/8" ply is the reason for the leveling you need to do, you will have bypassed the leveling step. Second, you'll be able to see what kind of shape the floor underneath is in. Make sure you don't have any rotten places that might cause you problems and verify that everything is screwed/nailed down properly.

Having said all that, if you intend to leave the 3/8" ply in place, you would put down the backer board first, then level on top of that. How far out of level are these places? You may need to do some work on that first if they're very far out.

Have you checked to make sure your joists are suitable for a tile installation? If you can give us the specs, we can tell you. We need to know the size, species, unsupported span, and spacing between joists.

[hookknife]

What Kman said

[Sean Moore]

yeah, listen to kman.

get that underlay out of there (the thin stuff with the glue) and see what your double (?!) layer of 3/4 looks like. Rot is bad.

[xoffers]

Joists are 2 X 8's, 16 on center with a 12' span from the foundation to support beam in middle of basement. The majority of the floor is approx. 4.5 X 12 with spots at each end of tub at about 6" wide, 12' span is running with floor joists. The house is a log cabin that had new subfloors spliced in in certain spots due to water damage years ago so the room I'm working on has solid flooring then about one foot in from the edge of the house is some other subflooring in good shape but about 1/8" lower so I figured I'd level that out and bring it up to the height of the main subfloor. I can't tear out the lower section of subfloor that runs next to the outside wall since it goes under the logs and if I tear out the 11/32 then it will be about 2/8" lower.

The joists are pine


Also, I'm at work now so I can't measure the subfloor but if I have 2 sheets of 1'2" ply and not 3/4" how would that change things. probably need to add another 1/2" of ply?

[Sean Moore]

at least take some out at the problem areas: Corners of tub/entire length of shower pan/toilet.

That's one thick floor if you're working with 1 7/8.

[Kman]

If you wanted to take out the 3/8" you could use a reciprocating saw as close to the wall as you can get. You would just have to be careful not to cut any lower than the top layer of floor.

[Sean Moore]

From the description I think it's got 3/4 under walls, then 3/4 + 3/8 in this bathroom, within walls. Could be wrong but that's what I got from the " I can't tear out the lower section of subfloor that runs next to the outside wall since it goes under the logs"

Standard log home stuff, it sounds like. Maybe it's got slate on the main floor and that's why the subfloor is so thick in the bath. We will know more as he posts.

[xoffers]

Kman said If you wanted to take out the 3/8" you could use a reciprocating saw as close to the wall as you can get. You would just have to be careful not to cut any lower than the top layer of floor.

yeah, that's what I'm thinking, I just didn't want to go there, trying to get this done while baby is with wife and at daycare!
I was right the first time, the floor below is 2 layers of 3/4 so is that an appropriate thickness before the backer board and tile?

Thanks Kman

[xoffers]

Sean Moore said From the description I think it's got 3/4 under walls, then 3/4 + 3/8 in this bathroom, within walls. Could be wrong but that's what I got from the " I can't tear out the lower section of subfloor that runs next to the outside wall since it goes under the logs" Standard log home stuff, it sounds like. Maybe it's got slate on the main floor and that's why the subfloor is so thick in the bath. We will know more as he posts.

That's correct, right now the floor next to the wall comes out about 12" and is about 1/8" lower than the main floor, what I was told by a friend who knows the house is that the original subfloor was rotted out from a damp dirt floor basement, so about 10 years ago the basement was redone in concrete and is now 100% dry and the house was more or less gutted and the old subfloor was entirely cut out and replaced minus a 1' border around all the exterior walls which is the old double 3/4" and still solid but lower.

[Sean Moore]

xoffers said That's correct, right now the floor next to the wall comes out about 12" and is about 1/8" lower than the main floor, what I was told by a friend who knows the house is that the original subfloor was rotted out from a damp dirt floor basement, so about 10 years ago the basement was redone in concrete and is now 100% dry and the house was more or less gutted and the old subfloor was entirely cut out and replaced minus a 1' border around all the exterior walls which is the old double 3/4" and still solid but lower.

OK, so everything else is on top of that? A good poking with a sharp awl (you can make one out of an old screwdriver with a bench grinder) can show you where you might have some moisture problems. Stab it hard, Normon Bates HARD. You can hear stuff below if you are stabby enough.

If you do find some soft/hollow spots in your bath there shouldn't be any need for a saw around the edge to lift a little corner of the underlayment and see what's going on, it's probably all within the perimeter of the walls. Might be under the baseboard. Just cut the corner out with your circular saw set to the depth of what you're cutting.

I don't know tile but I do know cabins. if you don't find anything soft with a good hard shanking do whatever Kman says, he knows his stuff.

[TwoStar]

xoffers said Joists are 2 X 8's, 16 on center with a 12' span from the foundation to support beam in middle of basement. The majority of the floor is approx. 4.5 X 12 with spots at each end of tub at about 6" wide, 12' span is running with floor joists. The house is a log cabin that had new subfloors spliced in in certain spots due to water damage years ago so the room I'm working on has solid flooring then about one foot in from the edge of the house is some other subflooring in good shape but about 1/8" lower so I figured I'd level that out and bring it up to the height of the main subfloor. I can't tear out the lower section of subfloor that runs next to the outside wall since it goes under the logs and if I tear out the 11/32 then it will be about 2/8" lower. The joists are pine Also, I'm at work now so I can't measure the subfloor but if I have 2 sheets of 1'2" ply and not 3/4" how would that change things. probably need to add another 1/2" of ply?

According to the Deflecto on johnbridge.com this floor is not rated for ceramic, just vinyl or wood. That is if I read the specs of the joist system right. 2x8, 16" on center, 12' span? Right? I don't believe that a thicker floor will help in this case. Of course, I am not an expert, engineer, etc.

The Amazing John Bridge Forums Deflect-O-Lator :-)

[xoffers]

TwoStar said According to the Deflecto on johnbridge.com this floor is not rated for ceramic, just vinyl or wood. That is if I read the specs of the joist system right. 2x8, 16" on center, 12' span? Right? I don't believe that a thicker floor will help in this case. Of course, I am not an expert, engineer, etc. The Amazing John Bridge Forums Deflect-O-Lator :-)

yeah, I just did the calculation. I'm guessing 12 feet but I'm not at home now, it may be 10 or 11' . Putting a support beam in would be no problem so I may go that route.

[TwoStar]

xoffers said yeah, I just did the calculation. I'm guessing 12 feet but I'm not at home now, it may be 10 or 11' . Putting a support beam in would be no problem so I may go that route.

I would also try the "bounce test". If you sort of bounce up and down and can hear the glasses jingling in the cupboard the floor won't work. A support beam would then be helpful...and necessary. Good luck.

[Kman]

One thing to keep in mind about the Deflecto on the JB forum is that it is well on the conservative side, meaning it will show a lower rating than what you really have. I guess the engineer that did the specs for it figured it was better to be safe than sorry.

There's another calculator on a different forum that is much more detailed and rates those joists (provided they are #2 southern pine and in decent shape) to be able to span almost 13 feet.

I did a ceramic installation years ago with the exact same specs, then ended up tearing it out on a whole-house remodel about seven years later and there wasn't a single crack in the grout or tiles.

Of course, it's always best to be on the safe side. A little overkill never hurts. If I wanted to beef up the floor just to be safe, I would get enough 2x6x8's to sister each joist, provided they don't have plumbing or wiring running through them. You only have to address the middle 2/3 of the joist, and this might be easier than constructing another support beam. The problem I've found with support beams is that it's easy to have it just a little too high, causing a peak in the floor. If you have access, sistering is the way to go. A box of screws and some construction adhesive and you can do one joist about every 10 minutes.

Two layers of 3/4" ply is waaaay more than enough for a tile installation, particularly over 16" joist spacing. I would still try to get rid of that 3/8" ply, though.