# For my personal house, porcelain tile install



## Dave in Pa (Oct 10, 2009)

Doing a new floor in the kitchen. I was going sheet good, BUT the wife wants tile now! YES DEAR!!!!!! 

I have 2x10 floor joist, 16" o.c., 3/4" plywood deck, 3/4" X 2 1/4" oak. 

My question is, 1/4" Hardie, then tile, OR remove oak, 1/2" Hardie then tile? I do have the room for the dishwasher etc. either way! If I remove the oak, there will be less to no transition to the dining-room oak flooring. I don't have a issue with the hump, but flush is better!

I was concerned or thought the oak would lessen the flex in the floor?

And now for the "killer" question, How many guys thin-set your Hardie down before the screws go in? I know that is what they recommend, I have done it both with and with-out, Just what would you do on your own place???

Thanks, dave


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## EricBrancard (Jun 8, 2012)

The hardwood needs to come up. I've never used cement board or hardie under a tile job on the floor. Usually 3/8" PTS with modified mortar. Sometimes a layer of Ditra on that.


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## avenge (Sep 25, 2008)

To the question "What would you do on your own place" Do you normally do hack jobs on your clients homes and want it done right on your own home or vice versa? If you're using Hardie it should be cemented down, when I use it I use 1/4" on flooring. The hardwood needs to be removed.


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## Dave in Pa (Oct 10, 2009)

avenge said:


> To the question "What would you do on your own place" Do you normally do hack jobs on your clients homes and want it done right on your own home or vice versa? If you're using Hardie it should be cemented down, when I use it I use 1/4" on flooring. The hardwood needs to be removed.


I know, I know, BUT!!! My back hurts! LOL 

I just wanted some "other" opinion as well, so
I can tell my BRIDE the issues'.

And, I do not do "hack jobs", been doing this for 35 years, flooring is not my strong point, that is why I am asking here for input to be correct. 

FYI, I will live in this house till I die!


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## ccoffer (Jan 30, 2005)

The reason you put thinset under CBU is to hold it UP, not hold it down. Any voids under the Hardi or whatever wind up being little trampolines that will give way if subjected to a point load. If the floor is dead balls flat, you can just screw down the backer board (or shoot it down with a coil nailer) but if not, you need thinset to create support for the assembly. And 1/2 inch backer board is for walls, not floors.


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## avenge (Sep 25, 2008)

ccoffer said:


> And 1/2 inch backer board is for walls, not floors.


There's no reason why 1/2" cbu can't be used on floors especially if it solves a transition issue. It's actually the other way around 1/4" is for floors not for walls.


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## ccoffer (Jan 30, 2005)

_There's no reason why 1/2" cbu can't be used on floors especially if it solves a transition issue._

Just like there's "no reason" 4 layers of 1/2 inch can't be used for the same reason.

Great catch. Thanks.


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## JazMan (Feb 16, 2007)

ccoffer said:


> If the floor is dead balls flat, you can just screw down the backer board (or shoot it down with a coil nailer) but if not, you need thinset to create support for the assembly.


Sorry, that is not true. All CBU's require thinset under them to fill any void and support the board. No exceptions. 

Dave in PA, What is the span of those joists? Do you know their species and grade? 

Another choice would be to install Ditra XL over the ¾" subfloor, then the tiles. (if the subfloor is in good shape). This would give you a smooth transition to the adjoining hardwood.

Jaz


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## Dave in Pa (Oct 10, 2009)

JazMan said:


> Dave in PA, What is the span of those joists? Do you know their species and grade?
> 
> 
> 
> Jaz


They are fir, 2x10, 16 oc, span approx. 12'8" with 1 row of wood bridging


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## We Fix Houses (Aug 15, 2007)

google Deflect -O-Lator


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## ccoffer (Jan 30, 2005)

_Sorry, that is not true. All CBU's require thinset under them to fill any void and support the board. No exceptions. _

No, genius, you're not. Geez, can you read? Your own sentence confirms what I wrote is true. The thinset is for voids. No voids, no need. I get that teacher told you "no exceptions". That isn't an idea. It's just brainless dogma.


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## charimon (Nov 24, 2008)

ccoffer said:


> If the floor is dead balls flat, you can just screw down the backer board (or shoot it down with a coil nailer)


What is this Mythical place you speak of? 
Next you will be leading us astray with fanciful tales of buildings with walls that are strait and plumb,
or that nails are just as good as screws.
Next you will be telling us that you don't have to tear out tile over concrete that has been submerged


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## BlueRidgeGreen (Apr 21, 2012)

I hear you guys (guys who I have a tremendous amount of respect for, and who clearly know their trade as well as anyone could) say this all the time, with incredible conviction, but I honestly just don't really understand it.

I have done floors using 1/4" Hardie without thin-set beneath it a few times and have never had an issue. (good almost 20 years later.....rolled piano's and 6' radiators over them...etc.)

As far as "voids", which seems to be the reason for the extra labor of applying thin-set......

If a quality CA is applied liberally and correctly (consistent beading and in a pattern that allows total coverage (4" x 4" grid)), and the fairly flexible 1/4" Hardie is installed immediately and screwed down just as fast and with just as liberal an application of screws...

I really don't understand how voids could exist. (unless we are talking about a pretty bad subfloor)

I'm really looking for someone to convince me why this is a bad practice, because I still haven't heard anything that would dissuade me from continuing it in select situations.

Don't those wacky Canadians just chuck tile on top of the ply?

Thanks.....


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## ccoffer (Jan 30, 2005)

_Next you will be leading us astray with fanciful tales of buildings with walls that are strait and plumb,_

No, friend, I will not. When I spoke of perfectly flat plywood floors, I was being facetious. Of course there are none, but if there were(big if) there would be no need for thinset underneath.

I also wrote a great big giant lie and no one called me on it.

Hint: has to do with gaining height with cement panels.


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## charimon (Nov 24, 2008)

I was having fun with your onryness. and the way you like to couch the truth in inflammatory prose which is why i commented on your true statements and not your durock stack. now if they only made 2 3/4 cement board screws 
(or roofing nails) that would be a different story.


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## ccoffer (Jan 30, 2005)

I think what gets lost in a lot of these discussions is the amount of rigidity the tile installation itself adds to the assembly. We talk about the things that might make a floor fail while omitting that a properly installed tile assembly is a net positive for the building.

If I lived in a trailer park (again), I'd want to be in the trailer with mud walls.


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## Splinter (Apr 5, 2005)

Why is this even an argument? 

The manufacturer wants thinset under their panels when used on a floor, so it gets done. 

The reason is to protect against deflection from point loads, correct? Who could possibly judge a plywood subfloor to be dead flat? Plywood sheets even have variations in thickness themselves. 

And I agree there's nothing wrong with using 1/2" CBU on a floor if it helps with a transition issue. Obviously stacking four sheets is ridiculous and we all just ignored the comment.


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## ccoffer (Jan 30, 2005)

_ now if they only made 2 3/4 cement board screws
(or roofing nails) that would be a different story. _

Or trees made of steel.

CBU is dead weight. It adds nothing but weight to the assembly. Hardi beats the others in this semantic jackoff, but they all exist as glorified membranes through which your favorite bag of dirt can hydrate. I figure the lighter you can make a cement panel, the better it will perform.


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## Inner10 (Mar 12, 2009)

BlueRidgeGreen said:


> I hear you guys (guys who I have a tremendous amount of respect for, and who clearly know their trade as well as anyone could) say this all the time, with incredible conviction, but I honestly just don't really understand it.
> 
> I have done floors using 1/4" Hardie without thin-set beneath it a few times and have never had an issue. (good almost 20 years later.....rolled piano's and 6' radiators over them...etc.)
> 
> ...


Tile direct on ply is still somewhat SOP here, but now most jobs have that wacky orange waffle speced.


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## ccoffer (Jan 30, 2005)

_The reason is to protect against deflection from point loads, correct?_

Reason number two hundred and friggen thirteen that I hate tile. Da ignernse.

A point load is on A tile. At A point. Deflection usually means the floor is bending. That breaks grout joints and potentially breaks tiles.

Imagine a leg of a grandfather piano with nothing to hold it up but a piece of glass.


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## Splinter (Apr 5, 2005)

Sigh.. Yawn...


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## JazMan (Feb 16, 2007)

Re: post #8 & # 11, May I ask what you (ccoffer) are a pro at? It certainly isn't doing quality tile floors. Haven't you ever read the directions available from every CBU manufacturer on earth? Don't you understand the principle of why you have to spread thinset under the board? 

Not only are you wrong, but also rude. I guess you don't know what you don't know.

Jaz


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## CO762 (Feb 22, 2010)

Dave in Pa said:


> I know, I know, BUT!!! My back hurts!


And you want to do a tile job?  Tile, buckets of water, buckets of thinset...

Get a neighbor kid to take up the wood ($).
Figure out what kind of tile you're going to use then get the underlayment that will help match whatever you're joining into.
Bond it and "do tiling".

You've been in the trades long enough to know how to tell if a floor is bouncy or not. Do that when you are standing on the subfloor and if need be, remedy the situation as you normally would.

I'm a (former) mud guy, so can't stand setting on plastic waffles. If not mud, then cbu or other options for non wood. Waffles are my last option. For non professionals in tile, I also recommend cbu over waffles because it's flat, so easier for them work with. 

There's a place for the waffles, but in those places there are often better options, but none usually available at the local big box stores so homeowners/non professionals benefit from that there.


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## CO762 (Feb 22, 2010)

BlueRidgeGreen said:


> I have done floors using 1/4" Hardie without thin-set beneath it a few times and have never had an issue. (good almost 20 years later.....rolled piano's and 6' radiators over them...etc.)
> ...
> I really don't understand how voids could exist. (unless we are talking about a pretty bad subfloor)


Because wood does move. The reason we use clips in roof sheathing for example. I'd imagine most of the time they won't be a problem, but for the amount of time/effort/cost of spreading thinset down before dropping a substrate on it compared to any potential future failures is not worth the trade off, IMO. 

I've seen hardie on floors that didn't do their seams, but the tile before still held fine. I just went over their underlayment as is once the HO signed something that released me from any future failures--meaning I only guaranteed my layout, not the viability of the install. Should still be good, but why not do it while you're there?

Cheap insurance.


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## avenge (Sep 25, 2008)

Splinter said:


> Obviously stacking four sheets is ridiculous and we all just ignored the comment.


I try and ignore all his posts.



JazMan said:


> Not only are you wrong, but also rude. I guess you don't know what you don't know.
> 
> Jaz


I'm a prick but at least I try and be smart while being one.:laughing:


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## CO762 (Feb 22, 2010)

Inner10 said:


> Tile direct on ply is still somewhat SOP here, but now most jobs have that wacky orange waffle speced.


Which shows how marvelous the shlooter machine has been in their marketing. If you can get to the architect level, you won't even have to sponsor a friendly internet tile board to push your product. But better if you do both.....Still laugh at the 'professionals' that pose next to their setting material or take pictures of it, like it's some sort of prize or 'look at me, I'm part of the group too!' Don't know if it's weird or creepy...or just an extension of high school....


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## ccoffer (Jan 30, 2005)

_"Re: post #8 & # 11, May I ask what you (ccoffer) are a pro at?"_

No, you may not. I will, however, give you permission to prove me wrong. I'm very benevolent.

Whenever you're ready, pro.

By the way, these are fine points, but they lead to an understanding of greater truths. I'm constantly amazed by how much goes over the head of the average tile "pro".

Now, I'll teach.

Backer board adds no rigidity to a tile assembly. In fact, it weakens the assembly because of it's weight/rigidity ratio. A 3x5 panel of something like 1/2 inch Durock runs around 70 cents a foot. An equivalent plywood runs about the same.

The reasons to use anything but more plywood are mostly ergonomic.


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## CO762 (Feb 22, 2010)

ccoffer said:


> Backer board adds no rigidity to a tile assembly. In fact, it weakens the assembly because of it's weight/rigidity ratio.
> ...
> The reasons to use anything but more plywood are mostly ergonomic.


I don't know what you mean with the ergonomic point, but you are correct that cbus aren't added for strength, they're added to provide a substrate that will be stable even when they get wet. If plywood/osb gets wet too much/too long, it will swell/delaminate.

They made boats out of plywood, but even though it was 'marine grade', they still covered the sheetstock with an impermeable coating. 

Don't know about the weakening it because while any weight added to something that is not structural will weaken it, I'd bet that if that becomes an issue for any tile, it's already too weak for tile. Don't have any numbers, just gut feeling.


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## ccoffer (Jan 30, 2005)

_I don't know what you mean with the ergonomic point,_

I mean simply that 3x5 pieces of score and snap cement are much easier to install than are 4x8 pieces of plywood. What you've written about the merits of cbu is in line with my understanding. If you look at a bar graph that represents the expansion potential of plywood, tile and cbu, plywood is the star atop the Christmas tree while tile and cbu are down there with the presents. There is a structural price to be paid, however, for using something that adds so much weight while adding no rigidity to the assembly.


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## CO762 (Feb 22, 2010)

ccoffer said:


> There is a structural price to be paid, however, for using something that adds so much weight while adding no rigidity to the assembly.


True, but while all those numbers can add up to mean something, the difference in structural support, as long as the load bearing members are sufficient, I think it's a moot point worthy of bar room or cookout conversation. 

And speaking of that, why are we debating these camel hairs again?


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## ccoffer (Jan 30, 2005)

Heh. I didn't know we were debating, though I think the correct term would be "negligible", not "moot". I just think it's important to understand the small things so one can extrapolate that understanding when addressing the big things.


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## CO762 (Feb 22, 2010)

ccoffer said:


> I just think it's important to understand the small things so one can extrapolate that understanding when addressing the big things.


 I completely agree with that. How the tile industry (and others sectors of course) has changed from knowledge to just product/gadget/widget driven has taken a lot of the knowledge out of it. 

I had a conversation with someone once about using a computer program to do something and he just said "push this button if you want to do ...." I said "my computer screen doesn't have those buttons, so can you tell me what you're doing in words?". He couldn't. It was pretty interesting.


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## ccoffer (Jan 30, 2005)

But there are things that are both interesting and depressing at the same time.


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## CO762 (Feb 22, 2010)

Some things more interesting. I like to note the human condition and the more eras I go through, the more interesting it becomes...or boring because it's just rinse, lather, repeat.

I've often wondered what Germany was like in the 1930s, and now I think I am better understanding it. That's sort of the stuff I'm talking about. Not depressed about it as I've had my run and am able to witness these things with a clear head and clear eyes. People usually get caught up in history rather than being able to observe it. That's pretty cool.


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## AustinDB (Sep 11, 2006)

sorry I stumbled into this thread, jeez 

"Why is this even an argument? 

The manufacturer wants thinset under their panels when used on a floor, so it gets done."

if the manufacturer states it as a requirement then I do it.


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## ccoffer (Jan 30, 2005)

Uggh. The reason to use it is not because someone wrote it on a piece of paper.


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## HS345 (Jan 20, 2008)

ccoffer said:


> _Sorry, that is not true. All CBU's require thinset under them to fill any void and support the board. No exceptions. _
> 
> No, genius, you're not. Geez, can you read? Your own sentence confirms what I wrote is true. The thinset is for voids. No voids, no need. I get that teacher told you "no exceptions". That isn't an idea. It's just brainless dogma.


Every manufacturer of CBU requires mortar under it. You really have no business giving advice about processes you are completely ignorant about.


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## HS345 (Jan 20, 2008)

ccoffer said:


> _"Re: post #8 & # 11, May I ask what you (ccoffer) are a pro at?"_
> 
> No, you may not. I will, however, give you permission to prove me wrong. I'm very benevolent.
> 
> ...


Wow, when I said you were ignorant in the last post, I really had no idea about the depth of that ignorance.

The voids are created *by *fastening the CBU, unless you intend to fasten it every inch.

If you think plywood is the best tile substrate, well, there you go again.


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## HS345 (Jan 20, 2008)

ccoffer said:


> Uggh. The reason to use it is not because someone wrote it on a piece of paper.


They have done far more than "write it on a piece of paper". Ever heard of a Robinson test? No? Didn't think so.


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## angus242 (Oct 20, 2007)

All this tile talk NOT in the tile section. Weird. Ya think someone with some buttons would fix this.

And we also have proof now to why some tigers eat their young. :blink:


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## angus242 (Oct 20, 2007)

BlueRidgeGreen said:


> I hear you guys (guys who I have a tremendous amount of respect for, and who clearly know their trade as well as anyone could) say this all the time, with incredible conviction, but I honestly just don't really understand it.
> 
> I have done floors using 1/4" Hardie without thin-set beneath it a few times and have never had an issue. (good almost 20 years later.....rolled piano's and 6' radiators over them...etc.)
> 
> ...


Well, 2 things here.

1) And please don't take offense to this but you asked for a reason so here it is. Some guys have more experience with tile than you do. That doesn't make a person like me "better" than you but it does mean that I have _seen_ more situations than you because that's all I do. I simply cannot give you every scenario where I've seen CBU fail. So if you respect a pro's opinion, I can unequivocally tell you, improperly CBU can (and does) fail...regularly.

2) So many times I hear the "I did it this way xx years ago and it hasn't failed...(yet)".
After many years of dishing out advice, this is the simplest way I can explain it to anyone. Tiling is a game of percentages. The more you do "correctly", the better odds you have against a failure. Can you install tile directly over plywood with Liquid Nails and come back to a perfect floor a decade later? Sure but that percentage is pretty small. Think of the gambling industry. If you had to be a casino owner or professional gambler, which side would choose? I'll take the house odds every time. 

To anyone that's demo'd a tile floor, you'd think the understanding that taking even a few "extra" steps over the bare minimum would help in how you install a tile floor. I know I sure as heck don't want anything to do with ripping up a floor I installed because I saved a few bucks or hours on the initial installation.

And personally, I'll never use CBU. If and that's a huge *IF*, it's spec'd for a floor and I'm a sub, I'll pay someone else to install it. Who the heck wants to deal with going to the supplier, putting on a cart, loading in the truck, unloading at the site, carrying into the floor and all that cutting of a cement-like product? Not to mention the extra thinset, mixing, bucket/tool cleaning and all those screws....

In my experience, the 2 biggest weak links I see in tile installations are CBU and cementitious grout. Both are products that _can_ work, there just seems to be enough "what ifs" between the 2 to make enough errors with both materials. Honestly, that weak link is the installer but there are enough guys out there that _also_ install tile. I mean isn't the fact that this thread exists proof that just because you can make a tile installation look good, does _not_ mean you are installing it correctly?


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## BlueRidgeGreen (Apr 21, 2012)

angus242 said:


> Well, 2 things here.
> 
> 1) And please don't take offense to this but you asked for a reason so here it is. Some guys have more experience with tile than you do. That doesn't make a person like me "better" than you but it does mean that I have _seen_ more situations than you because that's all I do. I simply cannot give you every scenario where I've seen CBU fail. So if you respect a pro's opinion, I can unequivocally tell you, improperly CBU can (and does) fail...regularly.
> 
> ...


Thanks for taking the time to answer. :thumbsup:

2 things though....

1) I get the idea of always trying to increase the odds for ANY type of installation.
But....
Does an increase from 99.8765% to 99.9965% really warrant that much more labor?


2) What are the physical reasons that a floor like this would fail? 
What is it about the difference between thin-set beneath CBU and CA beneath CBU that drops the probability of a long-term successful install so precipitously?
Some say "voids" (most don't even "say" anything other than..."don't"). 
I just don't buy the idea that CBU cannot be laid void-free, without thin-set (over decent sub-floors).


Basically, I agree with the estimation that more often than not, installer error is the culprit in most installations,
plus, I totally agree with the "aim for the bullseye" principle.
And...I haven't done it in many, many years, but I still want to know why I shouldn't.
*(If the answer is: You have seen it fail way too many times, even when executed as well as is possible, and the "why" doesn't really matter. Then I guess that would be enough for me.....coming from you.)*


(*3 .....Can we get to why you are done with CBU's sometime...... later? I'm already there with cementitious.)

(**4....Nice to have you back.)


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## GO Remodeling (Apr 5, 2005)

I seen cbd without thinset last years and others that have failed. The failed ones are generally over beams. I think the thinset supplies a sacrificial layer which accommodates some movement as well as fills voids. 

Further, the manufacturers all want the thinset under cbd. Probably to CYA. But someone would try to install without thinset over an old layer of thinset and after the tiles crack blame the manufacturer. But if they require it and you don't use it then you'd be on the hook for a failure for taking a short cut.

If thinsetting under the cbd is such a bother then switch to other products.


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## CO762 (Feb 22, 2010)

I agree that the installer is always the weak point and people can "do tile"...and not do it right but it will still sit there.

I like cbu but only use hardy in one situation.


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## ee3 (Feb 10, 2006)

KINDA LIKE A "GLUE LAM BEAM WITH OUT THE GLUE"
or SETTING 24"X 24" WITH A 3/32" TROWEL.


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## BlueRidgeGreen (Apr 21, 2012)

ee3 said:


> KINDA LIKE A "GLUE LAM BEAM WITH OUT THE GLUE"
> 
> or SETTING 24"X 24" WITH A 3/32" TROWEL.



I would say that a more apt description would be.....

Glue lam vs. a quad 2x12, glued and screwed in the field.
(Quad x12 is still aces)

24x24 doesn't play. Rigid with no mechanical fasteners vs. flexible with many.


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## angus242 (Oct 20, 2007)

BlueRidgeGreen said:


> 1) I get the idea of always trying to increase the odds for ANY type of installation.
> But....
> Does an increase from 99.8765% to 99.9965% really warrant that much more labor?


I assure you, the odds are MUCH lower than 99% if you don't follow manufacturer recommendations and industry standards. I'd put that number...FROM MY EXPERIENCE...closer to 60-70%.



BlueRidgeGreen said:


> 2) What are the physical reasons that a floor like this would fail?
> What is it about the difference between thin-set beneath CBU and CA beneath CBU that drops the probability of a long-term successful install so precipitously?
> Some say "voids" (most don't even "say" anything other than..."don't").
> I just don't buy the idea that CBU cannot be laid void-free, without thin-set (over decent sub-floors).


It's pretty simple; tile doesn't bend. If you get even a few 1/32s void under a corner of a tile, it surely can start rocking and eventually break bond. I once had the tiniest pebble come from a bag of thinset and made it past mixing and troweling. Ended up under 12x12 over Ditra and sure enough, within 2 weeks, the tile popped. The *smallest* movement can make a difference.



BlueRidgeGreen said:


> Basically, I agree with the estimation that more often than not, installer error is the culprit in most installations,
> plus, I totally agree with the "aim for the bullseye" principle.
> And...I haven't done it in many, many years, but I still want to know why I shouldn't.
> *(If the answer is: You have seen it fail way too many times, even when executed as well as is possible, and the "why" doesn't really matter. Then I guess that would be enough for me.....coming from you.)*


Like I said, the tiniest movement can create a failure. I have seen thinset under CBU but no taped seams and just that alone created a failure. But if you want a 1 sentence reason that will convince you, I cannot supply you with one. There are a lot of people smarter than me that have put this to the test under controlled environments and their extensive testing says what to do. It's not like a group of tilers were sitting around having cocktails one day and made up this "rule". 



BlueRidgeGreen said:


> (*3 .....Can we get to why you are done with CBU's sometime...... later? I'm already there with cementitious.)


Well, I kind of already alluded to that with my comments above. It's heavy, not easy to work with and offers no benefit to an install other than a good surface to tile to. The future is in membranes. And contradictory to some that claim membranes are neato toys, they are quite the opposite. As with most construction materials, things evolve. Why some people think that tile must be stuck in 1800 Italy is beyond me. I don't even want to be stuck in 1960. A membrane will handle a certain amount of in-plane movement. I mean, try to take a fabric membrane and pull it apart. Not happening. And as far as I know, all membranes are actually waterproof. But to talk to the bottom line which puts money in your pockets and helps you remain competitive against other installers. A membrane installs a heck of a lot faster than CBU. 
It takes me about 5 minutes to load 500sq ft of membrane into my truck. 
It takes about 5 minutes to unload 500sq ft of membrane to the site. 
Subfloor prep is the same regardless of underlayment.
I use 3 bags of thinset to install 500 sqft of NobleSeal.
The tools needed to install are a razor, 1/8" trowel and something to help embed the membrane into the thinset (roller, 2x4, wooden trowel, etc).
I can install the 500 sq ft of NobelSeal totally alone in maybe 2-3 hours. 
If I use GreenSkin, there is no thinset needed at all and drops the install time even more.

Only you can compare those times to how long it takes *you* with CBU.


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## superseal (Feb 4, 2009)

EricBrancard said:


> The hardwood needs to come up. I've never used cement board or hardie under a tile job on the floor. Usually *3/8" PTS* with modified mortar. Sometimes a layer of Ditra on that.


???


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## EricBrancard (Jun 8, 2012)

superseal said:


> ???


plugged and touch sanded ply.


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## HS345 (Jan 20, 2008)

EricBrancard said:


> plugged and touch sanded ply.


Of all the tile substrates, plywood is the absolute worst.


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## Rhode Island (Mar 24, 2015)

Refinish the hardwoods and be done


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## EricBrancard (Jun 8, 2012)

HS345 said:


> Of all the tile substrates, plywood is the absolute worst.


3/8" PTS with tile transisitions flush to 3/4" wood floors. When screwed off every 4 inches in the field and 1 1/2" along the seams, and used with modified thin set, it will provide a long lasting product. For large format tile, a layer of ditra over it for added insurance. 

CBU provides no strength. 5 ply plywood does.


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## angus242 (Oct 20, 2007)

EricBrancard said:


> 3/8" PTS with tile transisitions flush to 3/4" wood floors. When screwed off every 4 inches in the field and 1 1/2" along the seams, and used with modified thin set, it will provide a long lasting product. For large format tile, a layer of ditra over it for added insurance.
> 
> CBU provides no strength. 5 ply plywood does.


Why not just Ditra XL it and save yourself all the plywood cutting and 10,000,000,000,000 screws?


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## HS345 (Jan 20, 2008)

EricBrancard said:


> 3/8" PTS with tile transisitions flush to 3/4" wood floors. When screwed off every 4 inches in the field and 1 1/2" along the seams, and used with modified thin set, it will provide a long lasting product. For large format tile, a layer of ditra over it for added insurance.
> 
> CBU provides no strength. 5 ply plywood does.


Extra layers of plywood are always a good idea, adhering directly to said plywood is always a bad idea. Can it work, yes. As long as it is installed to the letter, with a high quality modified mortar (not just any old thinset). But there are too many variables, and no matter what, it doesn't handle moisture well, ever.


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## EricBrancard (Jun 8, 2012)

angus242 said:


> Why not just Ditra XL it and save yourself all the plywood cutting and 10,000,000,000,000 screws?


We seem to be heading in that direction actually.


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## EricBrancard (Jun 8, 2012)

HS345 said:


> Extra layers of plywood are always a good idea, adhering directly to said plywood is always a bad idea. Can it work, yes. As long as it is installed to the letter, with a high quality modified mortar (not just any old thinset). But there are too many variables, and no matter what, it doesn't handle moisture well, ever.


Understood.


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## ronkeddy11 (Mar 2, 2015)

It’s true the hardwood has to come out. As a DIYer I often encounter a challenge working with cement backer board when I try to cut the strong panels. I believe there are very less options for this.


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