Ceramic Tile Advice Forums - John Bridge Ceramic Tile

Welcome to John Bridge / Tile Your World, the friendliest DIY Forum on the Internet


Advertiser Directory
JohnBridge.com Home
Buy John Bridge's Books

Go Back   Ceramic Tile Advice Forums - John Bridge Ceramic Tile > Tile & Stone Forums > Tile Forum/Advice Board

Sponsors


Reply
Thread Tools Search this Thread
Unread 07-06-2007, 06:35 AM   #16
bbcamp
Registered User
 
Join Date: Jul 2002
Posts: 30,274
Bob, a single layer of 1/2" plywood is not a sufficient subfloor for tile. You need to add at least another 1/2" layer. This should be glued and screwed to the first layer so as to make a single 1" thick subfloor. Use yellow glue, not construction adhesive, and set the screw every 4 to 6 inches along the edges and 6 to 10 inches in the field.

The subfloor should be fixed before your set the tub, but can wait until later. install blocking betweed the joists at the edge of the tub if you decide to wait on the subfloor.

How long are the floor joists between supports? 2x6s are not very strong, so there are deflections issues that may need correcting.

One last thing: Do not get ahead of yourself. You may find yourself asking how to fix things later that you can easily avoid by taking your time and asking questions first.
bbcamp is offline   Reply With Quote
Unread 07-06-2007, 06:48 AM   #17
sinkholed
Registered User
 
Join Date: Jun 2007
Posts: 48
Quote:
Are you certain that your sub-floor consists of only 1/2" Luann? Firstly, Luann is not a suitable substrate material even if you could find it in 1/2" thickness. Next, your sub-floor needs to be a minimum of 3/4". For tile, you should then be adding a second layer (at least 3/8") laid perpendicular to the first.
Shaughnn
Was told it was luann, but it's definitely 1/2 or 5/16. Plumber/tile guy says it's good to go, which is bible for the wife, so I'm just trying to work with what I've got as best I can. Shim & fasten can tighten existing, but I want to do what I can before the tub installs tomw morning. I could probably add another 3/8 ply and then 1/4 hardi. I'll have to take my chances. Can I add this AFTER the tub?

--Bob
sinkholed is offline   Reply With Quote
Unread 07-06-2007, 06:49 AM   #18
bbcamp
Registered User
 
Join Date: Jul 2002
Posts: 30,274
Bob, ask your wife to join us, eh?
bbcamp is offline   Reply With Quote
Unread 07-06-2007, 07:12 AM   #19
sinkholed
Registered User
 
Join Date: Jun 2007
Posts: 48
Quote:
1/2" plywood is not a sufficient subfloor for tile...add at least another 1/2" layer...glued and screwed to the first layer...

The subfloor should be fixed before your set the tub, but can wait until later. install blocking betweed the joists at the edge of the tub if you decide to wait on the subfloor.

How long are the floor joists between supports? 2x6s are not very strong, so there are deflections issues that may need correcting.

One last thing: Do not get ahead of yourself. You may find yourself asking how to fix things later that you can easily avoid by taking your time and asking questions first.

Bob, ask your wife to join us, eh?
LOL! That will not happen. As it is I'm guilty of "not trusting the pro". I've got to compromise for the "best possible under the circumstances", which is tub goes in tomw.

I'm a little lucky that my span is not long, about 5-6' (not home to measure), since it's on foundation wall. I've got what you say about blocking if I add subfloor after tub install. Guess I should shim & tighten/fasten what I can before tub, then figure if I can afford the height differential of another 1/2 ply + 1/4 hardi + tile?

What about the moisture barrier behind the 1/2 hardi that will hold the tile on tub walls? Hardi goes right on the studs if I understand correctly, so is it just a 4mil poly from ceiling to floor? or do I have to extend under tub as well? Plumber claimed I could get away with just moisture face of insulation on the exterior wall, and nothing on the other 2 sides. Said I could add a poly barrier if I want, but don't think he expects the barrier on all 3 sides of the tub.

Thanks! ... and HELP!
sinkholed is offline   Reply With Quote
Unread 07-06-2007, 07:22 AM   #20
bbcamp
Registered User
 
Join Date: Jul 2002
Posts: 30,274
The vapor barrier is tacked to the studs before the backerboard is installed. Drape it into the tub a couple of inches, then install the board. Trim the vapor barrier, then embed it, the edge of the board and the nailing flange of the tub in caulk.

Make a series of cuts in the insulation's vaporbarrier so moisture doesn't get trapped between the plastic sheet and the paper face.
bbcamp is offline   Reply With Quote
Unread 07-06-2007, 07:27 AM   #21
Shaughnn
Trowel Monkey
 
Shaughnn's Avatar
 
Join Date: Jan 2004
Location: Kent, Washin'ton
Posts: 11,467
Bob,
You could also phrase it in these terms. "I may have not trusted THAT pro, but I've found many others who disagree with him also. Do you want to ask them any questions, Honey?"
We hear all too often "That's the way I've always done it" when installers are confronted about their questionable habits and tolerances. The tile industry says, after extensive testing, that your installer is incorrect in his assessment of your flooring. The tile industry also recommends, after extensive testing, that a moisture barrier be applied between the backerboard and your studs to contain moisture and reduce the potential for moisture-related damage. Exterior walls are one of those gray areas where "best practice" and "field experience" don't quite mesh because of condensation issues but the interior walls should get a membrane from somewhere above the showerline to overlapping the tub lip.
We make a point of not giving out "make do" advice here and we have a lot of pros bouncing around that double-check the advice that's offered. IF you have a problem convincing your wife, we'll be happy to explain things to her.
Best of luck,
Shaughnn
Shaughnn is offline   Reply With Quote
Unread 07-06-2007, 07:29 AM   #22
sinkholed
Registered User
 
Join Date: Jun 2007
Posts: 48
Quote:
The vapor barrier is tacked to the studs before the backerboard is installed. Drape it into the tub a couple of inches, then install the board. Trim the vapor barrier, then embed it, the edge of the board and the nailing flange of the tub in caulk.
So I can add the moisture barrier (4mil poly ok?) AFTER the tub is installed?

Quote:
Make a series of cuts in the insulation's vaporbarrier so moisture doesn't get trapped between the plastic sheet and the paper face.
Not sure if I follow. Just basically allow any moisture BEHIND the poly to pass through the insulation into the stud cavity?

Thanks!

--Bob
sinkholed is offline   Reply With Quote
Unread 07-06-2007, 07:36 AM   #23
bbcamp
Registered User
 
Join Date: Jul 2002
Posts: 30,274
Tub and shower walls allow much more vapor to pass through than other walls, since there is much more vapor and water there than elsewhere. Water will go through the grout lines, even if you seal them. Therefore, a plastic sheet is used to intercept the water and allow it to return to the tub by re-transmission when the shower is not in use.

Having 2 layers of vapor barrier will trap moisture. Murphy's Law is in full effect; water isn't supposed to be there, but it gets in and can't get out. The plastic sheet you install over the studs is a better vapor barrier, so it makes sense to defeat the one supplied on the insulation. What little moisture that would get in there is insignificant if it is allowed to pass to the exterior.
bbcamp is offline   Reply With Quote
Unread 07-06-2007, 08:29 AM   #24
Tom Tee
Registered User
 
Join Date: Jun 2006
Location: Wilmington, Delaware
Posts: 987
Re 4 mil. I am not a shower qualified person however I have a fair amount of moisture training. The thinnest poly cloth advised for moisture abatement is 6 mil, w/ 8 mil also recomended for floating wood or laminate flooring.

You are at a very serious cross road w/ this project with very heavy consequenses either way.

Keep peace in the family with sure distruction of the bathroom shortly to follow.

or...

3/4" on bottom and 3/8" or 1/2" or 3/4"(my choice) on top with a tempory lack of domestic tranquility.

If you wife will not be able to join us, Dr. Tom would recomend to do the floor right and have the fight. Fights come and go. Especially if you are like me and have the tub out for a long time. Wives have this thing about keeping the house nice and it took me a long time to incorporate this in my thinking to my own loss. A counsler friend mentioned that ladies frequently have their personally identity knitted to the presentation of their hiome.

Tubs falling through the floor pulling the plumbing off the studs-----now that's a real problem. If you really want to have a fight with the misses this will do it, you may need to wait a few months for it to happen but happen it will.

Do the floor right and in years to come you all will be laughing at the situation.

tt
Tom Tee is offline   Reply With Quote
Unread 07-06-2007, 12:17 PM   #25
sinkholed
Registered User
 
Join Date: Jun 2007
Posts: 48
I'll ask the Mrs. to review all this good advice. And, truth be told, she's not the only one wanting NOT to rip up the existing 1/2" subfloor. This whole bathroom remodel has to OPERATIONAL in 4 weeks. Sounds like more than enough time, but not really. The tub is tomw -- BEFORE the plumber/tiler goes on vacation -- and the tile / toilet / sink starts on the 25th AFTER he comes back. I guess we could try to hire another plumber / tiler, but that just ain't gonna happen w/o a

So, against the better judgements of the pros here, this is what I'm going to hope works:

1) shim & tighten up existing subfloor;
2) add 3/4 ply on top (glued & nailed as has been described);
3) plumber installs tub; finishes roughing pipes
4) 6 or 8mil poly tacked at top of 3 tub walls; hang couple of inches into tub;
5) finish roughing electric
5) 1/2 hardi on tub walls; trim poly to just lower than hardi;
6) 1/4 hardi on floors; will be confirming proper install of this;
7) greenboard (or paperfree alternative) on walls outside tub
8) plumber returns for finish tiling & fixtures

Thanks again, I need that good luck. I'll post back on this thread as it progresses.

--Bob
sinkholed is offline   Reply With Quote
Unread 07-08-2007, 10:40 PM   #26
sinkholed
Registered User
 
Join Date: Jun 2007
Posts: 48
Tub did NOT arrive on Friday. Plumber installed the tub/shower control and stub capped my supply lines to toilet & sink today (Sunday). Meanwhile my son & I installed joist-bracketed 2x4 brace supports to all the subfloor seams that weren't supported by joists. Existing subfloor really tightened up; no noticeable flex anymore. Wife agreed to adding 1/2 ply and then 1/4 hardibacker, which went down easy once the plumber endorsed it. Hopefully can add the 1/2 ply before the tub arrives, hopefully on Monday, the last day my plumber has for install before his vacation. Otherwise me & my boy are gonna have to install the tub ourselves.

Keep you posted. Thanks all.

--Bob
sinkholed is offline   Reply With Quote
Unread 07-14-2007, 01:52 PM   #27
sinkholed
Registered User
 
Join Date: Jun 2007
Posts: 48
Question Anyone explain uncoupling to me?

Guess I'm dense, but I can't fathom how a 2nd layer of plywood and/or CBU can serve to uncouple it, or the finished tile itself, from the subfloor.

Here's my apparently flawed thinking:

--If the plywood subfloor is nailed to the joists, and
--If a 2nd plywood is glued &/or screwed to the 1st (but not to the joists),
--Then how is it that the 2nd sheet is "uncoupled" from the 1st?

Hasn't the spreadable glue (ie: Titebond II) between the 2 sheets effectively laminated them together? If lamination is the desired effect -- and all the screws do is act as dozens of tiny "clamps" holding the 2 sheets together until a void-free lamination occurs -- then haven't all we've done is simply created a 1" piece of ply from 2 pieces of 1/2" ply? How is this at all different than if one had just installed a single 1" piece of ply to begin with? Where has any uncoupling been added?

--Bob
sinkholed is offline   Reply With Quote
Unread 07-14-2007, 02:25 PM   #28
jadnashua
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

 
Join Date: Jul 2004
Location: Nashua, NH
Posts: 14,057
If you glue the second layer down, then yes, it doesn't decouple things. It makes the subfloor stiffer than just adding a second layer, but doesn't add to the decoupling. Gluing the two layers together is not a recommended installation procedure, though. This has been answered many times, and a search would work, but, for a stone application because they aren't as homogenous (i.e., veins, cracks, minor imperfections) as a ceramic tile, the little lever action of the ends of the ply at the joist can push up enough to crack tile. Putting a second layer over it with the ends staggered so they are NOT over the joists, and then not anchoring them to it decouples that small but significant movement of those edges from telegraphing through the tile and fracturing them when done right.

Now, decoupling the subfloor from the tiling substrate, a membrane or cbu works. While the cbu is screwed to the floor, over time it actually crushes the area around the anchors and the tile and cbu float as one unit.
__________________
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
jadnashua is online now   Reply With Quote
Unread 07-14-2007, 10:34 PM   #29
sinkholed
Registered User
 
Join Date: Jun 2007
Posts: 48
Maybe I shouldn't really be worrying about wrapping my mind around how decoupling works, and instead just concentrate on knowing where & how I go about getting it in my particular installation.

Is the gist of it that I can achieve a decoupling effect at either one of the two points where my flooring layers meet:

-- between the subfloor and a 2nd layer of ply (if I don't glue)?; or
-- between the 2nd layer of ply and the CBU?

Quote:
If you glue the second layer down...[i]t makes the subfloor stiffer than just adding a second layer, but doesn't add to the decoupling. Gluing the two layers together is not a recommended installation procedure, though.
I think I want to glue. I've only got 1/2" ply as a subfloor and I want to add another 1/2" on top of that. If gluing makes for a stiffer plywood sandwich, then I guess this is an instance where it WOULD be recommended to glue?

Quote:
the little lever action of the ends of the ply at the joist can push up enough to crack tile. Putting a second layer over it with the ends staggered so they are NOT over the joists, and then not anchoring them to it decouples that small but significant movement of those edges from telegraphing through the tile and fracturing them when done right.
I actually think I understand this staggered placement. When I read this reply it made that last little bit of sense that broke through my dense skull. I went back and re-read the "liberry" link and it's all right there

Quote:
Now, decoupling the subfloor from the tiling substrate, a membrane or cbu works. While the cbu is screwed to the floor, over time it actually crushes the area around the anchors and the tile and cbu float as one unit.
So I guess the 5/16" Durock I'm putting down will be my uncoupling layer.

Thanks

--Bob
sinkholed is offline   Reply With Quote
Unread 07-14-2007, 11:01 PM   #30
jadnashua
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

 
Join Date: Jul 2004
Location: Nashua, NH
Posts: 14,057
You are looking to perform three operations: make the subfloor stiff enough, make sure any movement is inhibited from telegraphing through the subfloor to the tile layer, and give the tile something that it can stick to well and has the same characteristics of expansion and contraction. The cbu will expand and contract the same way the tile does, but different than that of the plywood. WHen these differ, the screws actually crush the cbu a little, allowing for some horizontal movement, but since it is held together with the taped seams and the tile on top, the cbu and the tile move together, keeping things intact. this is why you can't do that with solid dimensional lumber underneath...it can move way too much, warp, twist, bend, and that will telegraph through the cbu into the tile and grout and mess up the install. Various membranes can perform a similar action - Ditra being one of them.
__________________
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
jadnashua is online now   Reply With Quote
Reply

Stonetooling.com   Tile-Assn.com   National Gypsum Permabase


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 09:29 PM.


Sponsors

Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright 2018 John Bridge & Associates, LLC