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Old 07-13-2012, 01:38 AM   #1
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Ceramic Tile Floor Info Help


I've got a pretty plain vanilla installation of ceramic tile in a bathroom. The tile area is 62.5" x 59". I plan to use 13" x 13" tiles, about 1/8" thick. I've had some contractors in (my wife is highly leery of me doing this), and not surprisingly, am getting slightly different installation details.

The bathroom is in a condo built in the mid-1960s. The building itself is a "garden style", all wood, four-story walkup. We're on the third floor.

The original floor was tile on mud, but it had rotted out. I removed everything, including most of the subfloor. Next, I glued and screwed a bunch of 2x12s between the 2x8 joists (standard 16" on center) to reinforce the floor. I then put down 1/2" plywood for the subfloor, using PL subfloor glue and 1-5/8" screws. (Yeah, 5/8" would have been better, but some of the original subfloor was still there, and I didn't want to have different subfloor levels.) When I installed the 1/2" plywood floor, I tried to ensure it was both dead level and dead flat. For the most part, I succeeded, although at a distance of about a foot from the wall behind the toilet, the floor drops off about 1/8".

First off, should self-leveling compound be used to deal with 1/8" drop-off towards the wall behind the toilet?

Next, there's the question of the toilet flange. Depending upon who's doing the measuring, the top of the toilet flange is 1.5" to 1.75" above the new subfloor. I make it 1-5/8", maybe 1-11/16".

Question: where should the finished floor be in relation to the toilet flange? From research, it is clear that having it below the floor is dead wrong. Flush seems right. Others say the finished floor should come just under the bottom of the flange (thereby placing the top of the flange about 1/4" above the finished floor). Too high (1/2" or more) also seems to be a no-no, as that risks the toilet not resting solidly on the floor. After all my research, I get the feeling that having the finished floor either flush with the top of the flange or even with the bottom of the flange is OK -- it's a bit of personal preferance. Any thoughts/corrections?

Whatever the answer, I now need to calculate the "layers". Here's some questions related to that:
  • How thick is thinset? Yes, I know that this is a function of the notch size, but for a given notch, what will be the height when the tile is laid down? I think a 1/4" x 1/4" notch will result in the thinset being about half the height, or 1/8". Is this correct?
  • The plan is to install cement board after "padding up" as necessary with plywood. I plan to specify 1/4" Hardibacker board. Should the Hardibacker board be installed with thinset and screws, or just screwed to the plywood below? I'd think thinset would be required to deal with any slight depressions in my supposedly dead level/dead flat floor (and more to the point, if SLC is NOT used, to deal with that 1/8" drop off towards the wall behind the toilet), but ...
Now, regarding that "padding up" plywood, is this just screwed into in place, or should both subfloor glue and screws be used? If 1/2" plywood is laid down, what size screws, 1-5/8"? If 3/4" plywood is needed, should 2" screws be used? Should the screws go specifically into the joists, or does it matter? How far apart should they be placed -- every 6"? 8"?

In addition, for both the plywood and the HardiBacker board, should these go all the way to the wall's bottom plate, or stop just short of it to allow for expansion? If just short, what should be the gap? Should the gap be caulked (my preference: GE Silicone II) to prevent errant water making its way down to the unit below?

Lastly, should a crack membrane be put down (I'm thinking RedGard)? The HardiBacker board is "waterproof", so that's less of a concern. And, with all my 2x12s between the joists, the floor is pretty darn solid. Plus, after 45+ years, the building should have finished settling. Nevertheless, the building construction is wood ... Any thoughts?

I apologize for the above length, but I wanted to give all the relevant details, and get all the questions on the table upfront. Your thoughts / comments / suggestions -- and expertise! -- are greatly appreciated.

Richard
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Old 07-13-2012, 07:11 AM   #2
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Ceramic Tile Floor Info Help


Richard, backer board is not water proof, it will ruin if it gets wet enough.

1/2" is not acceptable ply for tile. Add more ply and use ditra mat for bond of the tile if cbu will raise the floor to much.
If you add 2nd layer of ply run it the other way With but seam in middle like you have the 1st layer but the other direction.

Do you think you can sister the joist to raise that slop instead of slc it?.....


Last edited by JetSwet; 07-13-2012 at 07:16 AM.
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Old 07-13-2012, 10:53 AM   #3
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Ceramic Tile Floor Info Help


Should have been at least 3/4 T & G subflooring that's installed with constrution adhesive on top of the joist and screwed down with ceramic coated deck screws, that a layer of underlayment rated plywood at least 3/8" thick (1/2" is better) that gets nailed down every 4" on the edges and 6 to 8" in the field.

Tile is a one shot deal, if the subfloor sags or moves at all the grout will fail and the tile will crack.

By just adding another layer of plywood over a 1/2 subfloor I've seen it act like little more then 1/2" shims sitting on the joist and it is lower between the joist. Any gaps between the layers in going to flex.
When I do A tile job I only want to do it once so tend to over build it.
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Old 07-13-2012, 12:15 PM   #4
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Quote:
I plan to use 13" x 13" tiles, about 1/8" thick.
I doubt you will ever find a 13" X 13" ceramic tile that is only 1/8" in thickness.
Quote:
Yeah, 5/8" would have been better, but some of the original subfloor was still there
And 5/8" would have also met current codes.
Quote:
First off, should self-leveling compound be used to deal with 1/8" drop-off towards the wall behind the toilet?
Not necessary in this case. Get the cemnt board (Hardi) installed then float-out some thinset. End of issue.
Quote:
Question: where should the finished floor be in relation to the toilet flange?
Anywhere from 1/4" below finished tile to 1/4" above finished tile. NO MORE.
Quote:
How thick is thinset? Yes, I know that this is a function of the notch size, but for a given notch, what will be the height when the tile is laid down? I think a 1/4" x 1/4" notch will result in the thinset being about half the height, or 1/8".
Basically correct - close enough.
Quote:
Should the Hardibacker board be installed with thinset and screws,
ABSOLUTELY use thinset, screws or nails are optional.
Quote:
In addition, for both the plywood and the HardiBacker board, should these go all the way to the wall's bottom plate, or stop just short
Stop short about 1/4" with the masonry products. I would then lap a small portion of the wall and the floor with KERDI Band to create a waterproofing effort.
Quote:
The HardiBacker board is "waterproof",
No it isn't. Don't kid yourself. Backerboards are not damaged by water but they certainly ARE NOT waterproof. For this reaso Redgard could then be used to coat the entire floor and slightly up the walls on the KERDI Band.You could use a flexible caulk in place of the KERDI Band but Redgard WILL NOT attach itself to 100% silicone, period.If caulk is chosen I would use an exterior 25 year caulk. You can paint Redgard over that.
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Old 07-13-2012, 12:16 PM   #5
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What the hell is the: &quot crap all about? Something isn't working properly.
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Old 07-13-2012, 12:31 PM   #6
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Ceramic Tile Floor Info Help


Thanks for the replies.

Right now, I'm thinking what needs to go down is another layer of plywood (3/4" this time), then 1/4" backerboard with 1/8" thinset, then 1/8" tile with 1/8" thinset. This will result in a total thickness of 1-3/8", which is just below the top of the flange.

JetSweet, your help with the following would be greatly appreciated:
  • If backerboard isn't waterproof, should I definitely RedGard it?
  • The current plan has total plywood depth of 1.25". Are you saying that rather than put down 1/4" backerboard, I should put down more plywood (say two layers of 5/8" plywood), then use Ditra?
  • I'm not familiar with the term "sister the joist". Could you tell me what this involves?
JoeCaption, I hear you that I should have put down 3/4" tongue and groove plywood when I had the chance. As the saying goes, experience is what tells you not to make the same mistake a second time! Given the current situation, can I retrieve things by putting down tongue and groove over the new 1/2" subfloor? Also, I noticed that you mentioned using nails. Should I use them instead of screws? (I'm a lousy nailer so I tend to use screws despite the greater cost, but I'd rather do it right ...) Should I use subfloor glue as well?

Thanks for all your help!

Richard
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Old 07-13-2012, 12:37 PM   #7
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Ceramic Tile Floor Info Help


Bud,

Thanks for your reply as well -- it came in while I was posting my original reply.

I think you're saying I'm on the right track, but should definitely RedGard. Will do.

Couple of questions:
  • I hear that the backerboard should stop 1/4" from the wall. Should the plywood as well, or should it go all the way?
  • When you say float out some thinset to cover the 1/8" dropoff, should I do that under or over the backer board?
Thanks!

Richard
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Old 07-13-2012, 12:55 PM   #8
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Ceramic Tile Floor Info Help


Richard, yes the T&G only would of helped but it's a small bathroom and your 2nd ply layer perpendicular from 1st will help void the but seam from the 1st layer.

The choice is yours to use ditra or cbu and red guard it the only difference is the ply size to fit the hight but it sounds like you got it figured out from every one posting help for you.
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Old 07-13-2012, 01:55 PM   #9
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Quote:
I hear that the backerboard should stop 1/4" from the wall.
In general terms everything should have some room to expand. In a small bathroom common sense suggests that [not much expansion accommodation] is required. I wouldn't install the plywood "jam-up" tight against anything. The tile backer and tile should have the gap.

In a condo situation you may have rules (covenants) that require you to waterproof a bathroom floor anytime it is above the first floor. I have no idea what your rules command, if anything.

I personally think waterproofing the bath floor is a good idea if you are the one with the exposure and liability if there is a leak that results in damage to someone elses unit. But, to totally waterproof a space such as this is basically impossible. If you experience a catastrophic leak there isn't much you can do other than keep your insurance premiums paid.

Any attempt at waterproofing would be nothing more than a temporary stop-gap effort.

I would install the backer board, caulk the crap out of the juncture using siliconized caulk but NOT 100% silicone caulk. Then apply Redgard to everything especially at and over the caulked gap and up the wall slightly, hiding it behind the baseboard.

Quote:
When you say float out some thinset to cover the 1/8" dropoff, should I do that under or over the backer board?
This must be done on top of the cement board. If you do it below the cement board you won't be able to install the boards without wrecking the filler.

Quote:
then 1/4" backerboard with 1/8" thinset, then 1/8" tile with 1/8" thinset.
Don't get too anal with those measurements. Thinset under cement board isn't likely to consume a full 1/8" not is thinset under the tile.

I would like to know where you are finding 13" tiles that are only 1/8" in thickness. You should measure the tiles again if you feel the measurements are that critical.

The choice using nails as opposed to screws (or vicee-versee) is your choice. One is not (in this case) necessarily better than another.

P.S. Jet is correct about the lapping of the plywood joints. T&G plywood isn't totally necessary in this case and you would gain nothing from using it.
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Old 07-13-2012, 10:02 PM   #10
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Hi everyone, Hi Bud.

Thin set under CBU will be barely 1/16" using a thin mix with 1/4x1/4 trowel.

Jet keeps telling people to install the 2nd layer of ply parallel with the joists, which of course is wrong. You should offset the seams but the face grain should always go perpendicular to the joists. That is the orientation of the stiffest way to install all subfloors and underlayment.

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Old 07-13-2012, 10:50 PM   #11
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Quote:
Originally Posted by JazMan
Hi everyone, Hi Bud.

Thin set under CBU will be barely 1/16" using a thin mix with 1/4x1/4 trowel.

Jet keeps telling people to install the 2nd layer of ply parallel with the joists, which of course is wrong. You should offset the seams but the face grain should always go perpendicular to the joists. That is the orientation of the stiffest way to install all subfloors and underlayment.

Jaz
No need to bring the face grain into this because you got here late.
Thanks anyway Jaz
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Old 07-13-2012, 11:42 PM   #12
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All,

Umm, I was gonna ask about installing the additional 3/4" plywood in the same direction as the subfloor, albeit making sure the seams on the top layer do NOT line up with the bottom layer. The reason is that I want to use the larger Hardibacker board (4'x8') in order to place the CBU seam parallel with and close to the wall behind the toilet, and I take it that the CBU seam should be perpendicular to the the plywood seam. Yes, there shouldn't be a problem with a CBU seam in the middle of the floor, but I'm very respectful of Murphy's Law and so try to design out problems wherever I can. It does raise the cost slightly (about $15) but that's turning out to be a drop in the bucket. So, can I take JazMan's advice to lay the additional 3/4" plywood in the same direction as the subfloor?

Finally, Bud, you were spot-on about the thickness of the tile. That 1/8 inch must have been taken from another tile we were looking at. The thickness of the 13x13 tile is 5/16". Thanks for making sure I fly straight!

Richard
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Old 07-14-2012, 07:50 AM   #13
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Richard, you need to offset the seam of the 1st ply other words take the weakness out, grain face runs in 2 different way in ply, so your building strength not from joist but the 1 st layer.
This is the way I have been doing it for many years with no issues. Bottom line is you can run it same way as 1st but its silly you won't be able to off set it right.
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Old 07-14-2012, 10:55 AM   #14
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Face-grain is important in most all cases, listen to Jaz, he is offering the correct industry acceptable method. When lapping the seams, previous seams should be lapped by 25%. When placing fasteners those fasteners should be installed into the previous layer deliberatly missing all floor joists. Don't install fasteners used for subsequent layers directly into the floor joists. And don't use adhesive. Fasten only to the earlier product.

Wood grains do run in two different directions when plywood is assembled. Face-grains however always run in the same direction.

I wouldn't recommend cement board seams be placed in a "path". Meaning...any room will have a predetermined "path" where first steps are taken when entering the room and where typically everyone will walk and the floor will bear weight. Try to avoid those areas when installing CBU seams. CBU seams should be off and away in small rooms when possible.

CBU seams are to be taped with mesh tape and then filled and covered with thinset. Typically this can be simultaneously accomplished when installing the tile but the depth of the CBU seam should be purposely addressed with thinset.

There are standards already written for all of these techniques. If a person performs contrary to those standards without issue it doesn't make his actions correct or professional.

I have been scratching my a$$ for more than six decades but that doesn't make me a proctologist.

Last edited by Bud Cline; 07-14-2012 at 10:58 AM.
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Old 07-14-2012, 11:17 AM   #15
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@ bud, then how would the 2nd layer be placed if you were installing it. I understand what your saying but I personally think face grain hold little value on a second layer of ply.

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