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cowboyro
Premium
join:2000-10-11
Shelton, CT

Subfloor thickness for tile?

I'm in the process of re-building a bathroom. The existing subfloor needs to go as it is damaged thanks to a leak.
What would be the minimum total subfloor thickness suitable for ceramic tile? Joists are spaced 16", span is ~12ft.
I know that more is better, but I don't want a big level difference. The bedroom is 3/4" hardwood over 1/2" ply, so 1 1/4" total. I'm planning on installing heated floor and Ditra, so that's 1/4" to start with, add the thickness of tile and mortar and the total is at least 1/2". I'm thinking about using 2 layers of plywood for less flexing. Would something that totals 3/4" or so be enough? Maybe 3/8 over 1/2?



IIIBradIII
Comm M-E-L Instr

join:2000-09-28
Greer, SC

Why not use true backerboard instead of ply?



cowboyro
Premium
join:2000-10-11
Shelton, CT

said by IIIBradIII:

Why not use true backerboard instead of ply?

Backerboard doesn't offer deflection resistance, just a good bonding substrate.


IIIBradIII
Comm M-E-L Instr

join:2000-09-28
Greer, SC

Well the first layer of ply should be fine, but I'd then add CBU on top of that, ensuring that the seams are overlapped.

Here's a deflection calc if it helps: »www.johnbridge.com/vbulletin/deflecto.pl



cdru
Go Colts
Premium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7

said by IIIBradIII:

Well the first layer of ply should be fine, but I'd then add CBU on top of that, ensuring that the seams are overlapped.

He's already using Ditra, so there is no advantage to using a CBU.

I'd go existing 1/2", another 1/2", heating wire, ditra, tiles with the appropriate thinsets between all the layers of the sandwich. You'd be up ~1/4" at the threshold of the bathroom, but it's not uncommon to have some type of a transition there anyways so I don't think it will be a stumbling point or look wrong.


VioletVenom
Lets go Gators
Premium
join:2002-01-02
Gainesville, FL

1 edit
reply to cowboyro

5/8" min subfloor thickness for joists 16" O.C.

Edit: What dimensions are your joists? 2x8, 2x10?



cowboyro
Premium
join:2000-10-11
Shelton, CT

said by VioletVenom:

5/8" min subfloor thickness for joists 16" O.C.
Edit: What dimensions are your joists? 2x8, 2x10?

Not sure, I'm yet to measure. Likely 2x8.


VioletVenom
Lets go Gators
Premium
join:2002-01-02
Gainesville, FL

If they are 2x8 your deflection is going to be greater than recommended for tile (span, dimension, spacing). Without doing the math you could probably get away with 3/4" T&G ply, glued down to the joists of course (if they are 2x8s).



IIIBradIII
Comm M-E-L Instr

join:2000-09-28
Greer, SC
reply to cdru

said by cdru:

said by IIIBradIII:

Well the first layer of ply should be fine, but I'd then add CBU on top of that, ensuring that the seams are overlapped.

He's already using Ditra, so there is no advantage to using a CBU.

I'd go existing 1/2", another 1/2", heating wire, ditra, tiles with the appropriate thinsets between all the layers of the sandwich. You'd be up ~1/4" at the threshold of the bathroom, but it's not uncommon to have some type of a transition there anyways so I don't think it will be a stumbling point or look wrong.

Fair enough, I'm no expert.
--
»www.FlightSimWorld.com
Remember, there are old pilots and there are bold pilots, but there are no old bold pilots.
Flight Simulator


cableties
Premium
join:2005-01-27
reply to cowboyro

This may not help:

I went with 1/2" Permabase for substrate over 3/4" subflooring and used thinset, not mastic. Because I put a threshold (stone) at bathroom doors, I didn't care about height (it turned out a 1/4" higher than other floor but with carpet, it was not big deal).

*I really need to post some pictures...it came out really nice.
--
Splat



John Galt
Forward, March
Premium
join:2004-09-30
Happy Camp
kudos:8
reply to cowboyro

If you have enough room under the joists, install additional support for that area.

I faced much the same issue and installed additional pier blocks and posts to reduce the deflection. Worked fine and only took one additional day to accomplish.



cowboyro
Premium
join:2000-10-11
Shelton, CT

said by John Galt:

If you have enough room under the joists, install additional support for that area.

It's on 2nd floor, so no can't do...

robbin
Premium,MVM
join:2000-09-21
Leander, TX
kudos:1
reply to cowboyro

Schluter recommends a 5/8" minimum subfloor. Personally I would not trust that. What I would do is "let in" a layer of 3/4" between the joists. Fasten 1 x 2" nailers recessed 3/4" to the sides of the joists and install the 3/4" so it is flush with the tops of the joists. Then screw and glue a 5/8 or 3/4 inch layer on top.

What type of heated floor are you installing that the combined heated floor and ditra is only 1/4"?



cowboyro
Premium
join:2000-10-11
Shelton, CT

said by robbin:

What type of heated floor are you installing that the combined heated floor and ditra is only 1/4"?

From what I've seen the wires are 1/8" (or less) and Ditra is 1/8"

robbin
Premium,MVM
join:2000-09-21
Leander, TX
kudos:1

I don't think you are going to be able to install the heated floor wires in 1/8". Probably a good idea to decide on the product you will be using for that so you can check manufacturers recommended installation. In fact, I would think that the Ditra alone will be 1/4" (1/8 for Ditra and 1/8 for thinset).


MaynardKrebs
Heave Steve, for the good of the country
Premium
join:2009-06-17
kudos:4
reply to cowboyro

Use min. 3/4" glued & screwed plywood.

If you are lifting the existing subfloor anyway, you'll have the joist cavity open.

1) Make sure that any joists which may have been cut by a butcher plumber are repaired.
2) Make sure that you have blocking installed between the joists to stiffen the floor. Not further than 4' OC, and preferably closer than that.

If you have drain pipes in the floor cavity, you can
a) take a piece of blocking material (eg. 2x10) and 'locate' the drain pipe on the uninstalled blocking.
b) cut a hole for the pipe in the correct location
c) slice the blocking horizontally to create an 'upper' and 'lower' piece of blocking.
d) slide the lower blocking under the pipe and fasten to the joists, then install the upper piece of blocking.