Plywood thickness under tile

www.johnbridge.com/forums has many active tile setters. In the last quarter, the following forum members were recognized by their peers...not quite old-dried up wanna be's
Gary Kight- had a kitchen project that was the focus of a case study
John Cox- the featured 5 Star NTCA contractor
Carol (La Caroleuse) - one of four that was featured in an article titled "Women in Tile 2013".
Jon Donmoyer- now an NTCA regional director of a 9 state region.

They have far more active tile setters than have ever been on this site. Just because they don't agree with you, is no reason to trash them like you continually do...feeling insecure?

If you believe you must have a modified over Ditra, and that Kerdiboard's waterproofing is the orange layer, you do not understand the products. Believing that blocking can let you overload the structure is likely to come back to bite you eventually. Overbuilding costs extra...it proves you're a great salesman if you can talk people into it. I don't know why you feel special that products will work different in your operations when there are hundreds of thousands of installs that work perfectly fine without all of the 'enhancements' you feel are necessary.

There are regular Schluter training classes all over the US (never looked into Canada), either off-site at a convention center or at either their new distribution center in Nevada or the main office in Plattsburg, NY. All you have to do is get a regional rep to approve you to go...it's free once you get there - they pay for the hotel, food, and training. Since they don't have to ship as much, the classes at the fixed bases are a little longer and they cover more information, so it is worthwhile to take one of those sessions, if you can get there. Plattsburg is less than 4-hours away from me and sort of on the path to other places I go, so it was both convenient and not really much out of my way.

On www.johnbridge.com/forums, some pros only chime in when there's something unusual, the regulars cannot handle or get wrong. There's a lot of oversight to ensure what's said is correct, whereas I seem to be the only one to catch your strays from industry norms.

If the quantity of posts is anything, you're on track to be right up there after time. Anytime Terry asks me to stop, I'll bow out. Using this to promote your business, solicit consults, etc. seems to be kind of against the rules and self-serving. I'm not sure why Terry puts up with it, but it is his site.

FWIW, both Terry and John Bridge are friends, at least that's what I've been told, and they regularly point people here for plumbing questions. Before you, since it is more of a plumbing place, people would suggest that site as the one having more professionals on tile related issues, and the shower and bathtub forum here was more on suggestions of brands, and how to install them - not the tiling issues. And, to me this is important, you'll get more opinions and options there than here when it relates to tiling. I try to handle some of the more common, simpler issues, and will point people over there for more complex issues, or for more opinions. It's been that way for a long time until you came around and started to throw darts.

Another big difference, the people there do not use the site as a sales floor like you do, promoting themselves. They only show work when there's a question and an example can help clarify the answer. As a result, they tend to not have as many posts. A totally different dynamic.

As to blocking links, the sites are there for two reasons, as a service and to make the owner(s) some money. Clicks on the site to an advertiser only pay when they're done from the individual site. Your example of blocking a link is totally understandable, and is one reason why Terry blocks out references to places that he competes in - why should he allow posters to suck sales from him or click on an advertiser's link from another site rather than his own? So, your reasoning is way off as to why that block is in place.

This is not about moving higher on Google search, it's about accurate, reliable information. I start a thread when I have a question and point people to where they can get info if it's not readily available here in a timely fashion, or to get another opinion. You start one to sell you.

johnfrwhipple said:

Quit the John Bridge Site

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According to the moderators at www.johnbridge.com/forums John Whipple was permanently banned from that site on 02-20-11. At that time, John Whipple asked that all of his posts be removed, but that is not the policy of that site, and they remain.

That tirade is one example of why John was eventually banned. Unfounded character assassinations and insinuations to character. John Bridge was glad to see him go, and he is not welcomed back. Anyone who disagrees with John is obviously a hack, and has bad intentions. Talk about sad.

I don't hate John, I think he is somewhat misguided in that he thinks the manufacturers don't know their own products, and have a feel for how to use them, and John knows better and anyone who thinks otherwise is either a dupe or on the pay. The industry isn't wrong...

And, when John's comments contradict fact (like on what provides waterproofing on Kerdiboard), I call him on it, and he goes into a tirade about this and that.

We all make mistakes, John is just not big enough to acknowledge that or learn from it. I recognize I can, and have acknowledged that more than once over the years here...I learn from them and others, and since I'm around more, it's not hard to answer a question that is already been asked 100 times...it doesn't change, many people won't search, and they get their answer quicker than waiting for a pro to get off work to then decide to check...in that manner, assuming you have the time, you can rack up a lot of messages...helping someone get a quick answer to their question. And, more than once, I've said wait for some other opinions, or sent them to a place where I know they can get them.

But, I wish Terry would actually moderate this more, and most of this whole thread would go away...we've lost the point of the original discussion...do you NEED more plywood under the tile. The short answer is no, there are millions of floors installed in the USA and Canada that work just fine with what the original poster has. AND, they don't have blocking in their floors. Adding it adds dead load that has little benefit here. This assumes that what's there is in good condition, was installed properly, and is the proper type (either T&G or has the edges blocked for support). If it's not, the choice is either take what's there up and replace, or add some. The minimum you should add would be 3/8".

johnfrwhipple said:

Awesome - more personal attacks.

Thanks Jim!

Good to know a retired defense engineer is training us all on Schluter Installs. The nation's bathrooms are safe! Yeah Jim

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John, the only thing that sticks in my mind here with all your arguing is you basically calling old men dried up and useless. That's not true, as you will realize when you are older. Actually pretty funny. When you are in the rocking chair and somebody has to wipe the drool off your chin, well maybe, lol. Enjoy your and Jim's discussion.

The foam is the primary waterproofing layer of Kerdiboard, and when used in a wet situation, you treat the edges and any penetrations as if it were a seam, you use Kerdiband over them. John's worry about the backing of the orange layer is irrelevant if you follow instructions - it would be protected, and would not affect strength, as John alludes. Proper selection of the material for the task is important - thickness used depends on the application and whether it is applied to a surface where it needs to be self-supporting, or it is added like a surface and has a full thinset bond to it. In a non-load bearing wall, you should use 2" material and attach it to the cross section with their metal channel, and probably would want to use it also on the outer edge. When used as a countertop, it needs to be at least 1.5" thick, and can be attached to the top of say kitchen cabinets with KerdiFix and no further reinforcement is required. Penetrations for things like faucets require backing plates (typically a routed hole with a tile bonded in, then when you add your finish layer, that section has a load plate covered by the finished layer - i.e., two tiles thick, bonded into and onto the material).

The stuff is quite useful, nice, flat, easily cut, carried, and you can do things with it that are difficult to impossible with wood construction for say tub decks, and many other things. Hardly the junk that John has called it. In the one picture of a failed installation John posted, one only needs to look at the data sheet for Kerdiboard http://www.schluter.com/media/KERDI-BOARD-ENG-012013-Final.pdf?v=201310190601 where the max temp is 70-degrees C. Guess what temp steam is? At sea-level, water boils at 100-degrees C. Easily out of the range of the material selected. If you also read the data sheet, it calls the exterior surfaces "a special reinforcement material on both sides and fleece webbing for effective anchoring in thin-set mortar." Nowhere in there does it call it waterproof, or the primary waterproofing material. IF you understand the properties of extruded polystyrene, you'd know for practical purposes, it is waterproof, the thinset compatible layer also being just aids the overall robustness of the material in both strength and performance. The Germans take things seriously...they rarely deliver junk (which John as called KerdiBoard many times).

In the class at the factory in Plattsburg, NY, they specifically said you did not need to repair the surface layer if it was cut AS LONG AS IT DID NOT PENETRATE all the way through the material, since it was still waterproof. One would hope that the factory people understand how to use and install their product! This is the basis of saying the foam is the waterproof portion. Since that panel is not designed for things like a shower floor, or areas that are regularly submersed in water, there is little problem of saturating the back side of the material, and NO problem with it leaking through to the back side of the surface covering. FWIW, all of their linear shower sloped foam panels ARE covered with Kerdi fabric, because it is the PRIMARY waterproofing layer, even though the foam is as well.

So, let's see how John twists these words...his ego just can't accept he could be wrong.

Humans are fallible. I've admitted making mistakes before, and will admit, the person I talked with was not the instructor. But I'll stand on the point that KerdiBoard is a useful, viable product and that John doesn't understand it or how it should be used (he may yet learn, but we'd probably never find out about it!). Slope is required where it could flow to a non-waterproof area (a curb in a shower is a good example), or saturate a component that could be damaged, or cause damage to areas beneath it when it sees constant or copious amounts of water. Neither of those two things can happen in a waterproof Kerdiboard niche, if it is installed properly. If the niche was made out of something like cbu, that would be a major issue as the material could be saturated, and create problems. The nature of thinset means there's very little material that can absorb moisture, and very little ever gets there beneath the tile and the grout, and when it does, it meets up with a waterproof assembly. The niche would tend to dry any moisture that did penetrate. Personally, in that instance, I'm not all that worried about slope...it would be easy to add to the applied tile, and then 99% would run off, and the 1% that was left would evaporate quickly. The goal of the slope is to prevent pooling...if you read the installation instructions, they suggest adding slope to the tile to prevent pooling when installing the optional shelf, but it's not a bad idea on the bottom edge, either. Much todo about nothing.

FWIW, extruded polystyrene is a closed-cell foam, i.e., there is NO path for moisture through the material. Polystyrene material itself is also waterproof...so, you have a material that is itself waterproof that is covered by another waterproof layer on BOTH sides filled with closed cell bubbles created by the foaming process...damage the wet side, and you still have two significant layers of defense...the foam is waterproof. The surface, as stated in the data sheet, is added for strength and thinset compatibility. Another similar product, Wedi, is made up of the same material, but they use a special coating to provide thinset compatibility. And, if you look at their instructions, in making joints like the floor to walls, they tell you to create a rabbet joint, cutting into the material. If it wasn't waterproof on its own, that would not work. Similar, but not identical...when Schluter decided they wanted to produce a foam panel, they spent a lot of time and research coming up with one that had the properties they wanted, they did not want to clone someone else's product, and they didn't. There isn't a similar product out there with the properties of KerdiBoard (that I've been able to find, anyway), and therefore, people need an education on what it is and how to use it properly. That's why I went to the factory to take their class...get my info from people that know and understand the product and its nuances to application, and totally discount John's rant about it being junk.

Per Schluter's instructions,
"Where waterproofing is desired, the joints
and corners of KERDI-BOARD in the
area must be sealed with KERDI-BAND
using unmodified thin-set mortar. The
KERDI-BAND must overlap panel joints by
at least 2" (50 mm)."
"The instructions also say:
Fastener penetrations may be sealed
with KERDI-BAND using unmodified thinset
mortar."
What they don't say, is that they must be sealed if you want waterproofing. They did say that in the class. KerdiFix could be used, but cost-wise, the Band is often the better way. The Kerdi Shower manual is referenced in the KerdiBoard tech data sheet, and says to use that when building a shower which means any penetrations or seams need to be covered with Kerdiband with the requisite 2" overlap.

So, putting the edge of the board in water shows nothing, since if it is installed per the instructions, those edges are covered if it needs to be waterproof.

If you attend a Schluter training class, you learn not only the proper way to use their products, but pick up some tricks they've learned along the way, such as, a puncture that doesn't penetrate the entire board is still waterproof.

Any assembly not build as directed is not a valid test, such as your edge in standing water...proves very little. If you've installed it properly, the entire backing to the outer covering will never get saturated, so your test on strength is kind of irrelevant. One can take a product and subject it to conditions it's not designed for, and try to make projections of how it will perform when installed correctly, but often, those will be incorrect.

John still doesn't understand KerdiBoard.

johnfrwhipple said:

You write: "Seasonal changes may allow the wood to shrink after a dry hot summer...just depends. My unprofessional opinion." - I agree with both of these comments of yours some eight years ago. One wood dries and does shrink. It also checks and cracks. It is also total crap in a shower curb. This is why it's banned in Australia for shower curbs. This is why I use cement or bricks here in Vancouver. I also believe the later part. That your opinion in unprofessional. But I bet now eight years later you would say I like using Kerdi Curbs. Because your a Schluterville Graduate. OMG sad sad sad

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TCNA Handbook, 2012 edition, page 166 shows acceptable shower curb construction and says: "studs or cementious base for curbing" then shows a diagram.

It depends on the situation, like I said. I would not use studs on an unknown slab (many older ones did not have vapor barriers under them, and one does not know if they were compromised during construction even if they did), since there could be moisture coming up through the slab into the wood. Seasonal changes (spring is often much damper than say the middle of the summer) may make that choice poor. But, on a wooden subfloor, properly constructed, and tested by the TCNA, wood is an acceptable and reliable curbing material...another example of John's always right, but it conflicts with the industry standards - do it his way, or you're a dupe or a shill.

I would use pavers or brick to build a curb on a slab, or, if it met my needs and aesthetics, maybe a preformed one.

But, cutting and assembling studs for a curb is both faster and less expensive and has been used in millions of showers. The only time it becomes an issue is if the shower was not built right and they get wet...John's argument would also apply to the structure - if the studs are going to create such a big problem in a shower wall, shouldn't you support your walls with cement columns or brick towers or metal studs? Why are they good there? Because, you waterproof or control the shower moisture properly!

Using brick or pavers for all of your shower curbs is a waste of time and money....everything has to be evaluated which is why I keep saying risk/benefit/cost and some sanity need to be used when making a decision.

Another example of John throwing stones. And, if you'll also notice, I'm not the one telling people to do nasty things...

johnfrwhipple said:

Didn't factory worker tell you that the Kerdi Board Niche's have a slope as well.

If you handled a few of them and could not see a lack of pre-slope that is scary man. A Little Birdie told me you need glasses! LOL

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At a typical, industry standard 1/4" per foot, that two inch deep niche would have all of 1/24th of an inch difference back to front...not all that easy to see. You just like to poke at people...the installation instructions say you can slope your tile. THen, 99%+ is going to run off, and the rest will evaporate, and even if some does penetrate, the substrate is totally waterproof - there's not much room in the crystalline structure of the thinset for moisture to accumulate, and it really doesn't get there except maybe in places like a shower floor or where the showerhead hits...typically not right into your niche, except for maybe some splashes. Much talk about nothing. If this was made of some other substance slope or not would make a big difference, and, now that you've been told the bonding layer is waterproof (that's not in any of their documentation, it's only called a reinforcement layer and mortar bonding layer everywhere), you've got three layers of waterproofing. If you follow your installation method, you then add two more layers...just because you don't believe the things are waterproof in the first place. Extruded polystyrene is waterproof, and this is the core of Kerdiboard. Finding that the surface layers are also, is a bonus.

FWIW, from a Dow Chemical data sheet (emphasis mine): "The closed cell structure of the XPS foam makes capillary water absorption impossible. But water vapour movement is possible through XPS foam." http://www.isover.com/Our-solutions/Insulation-materials/Polystyrene-insulation sounds like waterproof to me.

Just to be clear, while John may have 'quit' www.johnbridge.com (which I find hard to believe since he loves to post things), they banned him, and he cannot log back in. As a result of whatever ticked him off, as a result, he throws darts anytime he can. There is a huge cadre of working, award-winning tile guys AND women over there, glad to help, regardless of what John says. For years, the shower and bathtub section of Terry's site was related to plumbing questions related to those rooms, not tiling, which John wants to be his personal domain...he hates any competition. Terry approved of people recommending that site for tile expertise, regardless of what John touts, and the people over there would suggest people there come over here to get expert answers to their plumbing questions, a good working relationship - go where the expertS are (i.e., more than one). This is the reason I link people to that site, to get a clearer choice of industry approved methods, not those that John decides is the only way to do things. As opposed to what John alludes, there are lots of people over there that can help you build nearly any type of shower, and the information in their library covers most of them, and there are people that have there preferences for pretty much all of them, so lots of varied experience. The TCNA handbook is several hundred pages long, describing the approved ways to build things or cover things with tile...each one has it's own cost/risk/benefit. John would have you do it his way, and the industry and experience of millions of installs over many years, that there is more than one way to do things and not have your world fail. The skills required to accomplish the task in any approved technique needs to be weighted according the your cost/benefit/risk tolerance and skill level. The task is detailed, but not hard, and there is more than one place to get information, and there is more than one right answer...John just doesn't think that way.

I freely admit I don't tile every day, but have some experience in more than one area. I have had some training, and have worked in highly technical areas most of my adult life where you need to evaluate the cost/benefit/risk of any decision. Over 30-years of that hones some ability to evaluate information and make good decisions, and to spot where someone is full of their own importance.

I'm sure John will make some snide remark. Just take it in context with his ego, his track record on other websites, and go from there.

With regards to creep, which is the deflection changes over time to a loaded structural member, some experiments were performed and documented in a doctoral thesis http://scholar.lib.vt.edu/theses/public/etd-12803097520/etd.pdf . Take a look at Figure 4.51, and notice how the deflection changes over time (creep) with the same load. The creep here was charted at about the typical design dead load. Later diagrams show other structures with various loads, but he creep clearly shows the structure continuing to bend over time up to approximately 150% of that in the first few months.

Excessively loading the structure means that you push the curve, and since the wood is only so elastic, the creep can end up larger as the structure is actually damaged, verses just flowing.

Feel free to read the whole thing (it's kind of boring, but if you understand at least some parts), it's easy to see that a load on a structure does not produce a finite, inflexible, static change...it creeps (increases over time). When you're dealing with an inflexible surface like tile, if you push the limits, over time, you may very well see failures exhibited by cracked grout, broken tile, and possible delamination. One other thing you'll find from the study, is that there hasn't been a lot of study of this effect, and this was an effort to try to find a mathematical model that could be used by architects and structural engineers to analyze and evaluate structures for long-term reliability.

Simplistic advice (the math can get really messy), avoid overloading your structure, weight is not your friend, deflection is real, and what you see in the load tables does NOT account for creep. There are consequences, regardless of what John Whipple thinks, of long-term creep to a structure, especially when you go over and above what the industry recommends. Risk/benefit/costs, you decide your tolerance, and don't shoot the messenger (please)!

I find it interesting that two Ph.Ds one of which is a well respected professor at a good technical college say the same thing, and John totally disregards it - maybe he couldn't understand it, therefore it doesn't exist or must be wrong. Long-term creep in wooden structure is a fact. The experiments performed as part of that dissertation are repeatable, and had multiple samples (unlike most of John's tests, where he came to a conclusion with one sample). Adding extra weight not called for in the industry guidelines adds to the problem. The load tables are derived without long-term creep accounted for, and they are based on a specific load (nominally 10#/sqft dead load). When you increase the dead load above those limits, your deflection increases and the margin you thought you had starts to evaporate, and the long-term creep rate could be a bigger factor. So, there's a cost/benefit/risk...adding extra stuff above and beyond what is required has a real risk. All I did was point that out, and then provided two independent, peer reviewed references that backed that up. Adding stuff for a good engineering reason certainly makes sense, but doing it arbitrarily, without understanding the risks, has its perils. You don't add stuff to an airplane to make it stronger unless it's needed, the costs aren't worth it. Same thing is true anywhere...are you willing to afford the costs and risks. I also find it funny that John disregards the TCNA guidelines on what has been tested, evaluated, and verified, as viable methods to achieve an end (take the curb issue he brought up). His way is the only way, anyone else's is crap, and unreliable. Same thing is true with Schluter and the use of Kerdi...as listed in the USA and Canada installation manuals (he does live here!), it meets all of the requirements for a reliable shower, but John feels he must augment that, calling it inadequate. This adds cost with no real benefit except to his bottom line (more labor, more time, more money) - certainly not to the customer. If he did it right per their tested, verified methods, it would work, and be warrantied by the factory. Maybe he doesn't trust his workmanship, and therefore needs those extra steps to guarantee it.

John hates, the www.johnbridge.com website, and anyone associated with it. Why he 'quit', when he had a forum to express his ideas, I don't know the full details, but he IS permanently banned from ever logging back in (at least they feel there's a good reason). And one other site had enough of his rants and character assassinations to ban him as well. Why I continue to point people over there if they have a question on tiling things, is that they have NUMEROUS working pros, with lots of real-life experience to offer opinions, here, we currently have one, very inflexible, opinionated one.

John still doesn't understand my points...

He thinks that I'm challenging his tile layout, bathroom layout, and execution of setting of the tile. All appear impressive from the pictures he posts and what most of the people look at in the end...

But, it's how he addresses the underlying structure and uses the materials underneath that are at issue. Why, for example, on a KerdiBoard niche that has three layers of waterproofing (front/back layer and the foam) does he feel it is imperative to then add two layers of Ardex stuff? Why does he require adding it to Kerdi? Why does he feel he needs to trash a product that has passed all unbiased independent tests that says it works? Why does he say that only things he cherry-picks in the TCNA handbook are the only way to do things? Why does he say that he needs to add extra material above and beyond what the industry that has proven it works as the only acceptable way to perform a job?

In his mind, he is always right, his way is the only way, and he slams anyone that says anything that calls him on it. The testing agencies do what they say, the manufacturers have a vested interest in staying in business with satisfied customers, why would they promote a method that didn't work?

Why are we to believe in light of all this that John's way is the best and only way to perform the task?

I try to point out where the industry says that's excessive, and it works just fine without those extra layers. They add costs, both in materials, and labor, and what John doesn't seem to want to accept, weight that can have some serious long-term effects.

Here's what the TCNA has to say about it...https://www.tcnatile.com/faqs/31-efflorescence.html
"Except in the rarest of cases, efflorescence does not occur from the small
amount of minerals in water used to wash a floor. Nor when tile is installed
with thinset (tile cement) are there enough soluble salts in the thinset to
cause efflorescence.

Occasionally, when tile is installed over a thick mortar bed, the mortar
could provide a sufficient amount of soluble salts to cause efflorescence but
only if moisture is regularly passing through the mortar bed.
"

You do not have a thick mortar bed over Kerdi, nor Ditra.

Without knowing what type of grout was used, or testing the material, this is not definitive proof of much.

The TCNA has inputs from all over the USA and Canada and representation from most manufacturers. I take their advice with more than a grain of salt. They actually test things and have the ability to analyze the results rather than guessing what happened.

I'm hoping you didn't build that shower, if you did, it's not a particularly good example of good skill! Pretty amateur cuts, and edges and alignments. So, we're back to what John says, verses what the TCNA says.

If tile setting was a beauty contest, I'm pretty sure that John would win. The point was and is, there is more than one way to do something and have it technically perform its intended purpose. John seems to feel his way is the best and only way - the industry says otherwise. The TCNA handbook is nearly three hundred pages long, listing many ways to do things, not one. These have been tested and used for longer than John has been setting tile, so why should we believe his is the only way to do it right?

Cost/benefit/risk. It appears that John's customers don't particularly care about costs. This is not a luxury the average person can afford. The benefits of doing it one way verses the other may not be worthwhile in any one situation, especially if it takes longer (important if you're paying for labor) or costs more. This is by no means a justification for skipping steps or not following the procedures accurately. There are conditions that dictate doing things a certain way, and applying a method where it is inappropriate is just that, wrong. But, often, there's more than one way to accomplish the same thing, but John just doesn't want to listen.