Fine Homebuildingers,
Sixteen years ago I built a colonial house with a 30×30 foot print using Radiant Tech heat tubes under the subfloor (installed in the basement). The house is in Vermont where the winters are cold. The floor is tongue and groove 3/4″ plywood with a layer of 1/2″ CDX on top of that with the ceramic tile finishing off the flooring system. The heating system works well. The flooring system is constructed with 2×12 with a fifteen foot span.
My problem is that I cannot keep the floor tile in place. After the first year or so the tile began buckling in the middle of the floor. Soon the floor required relaying since most all tiles had broken the bond from the 1/2″ CDX. I could lift the tiles right off the floor. This occurred in the middle of the winter.
This winter the tiles buckled once again. What seemed like overnight a patch of tiles popped up about an inch in the middle of the floor, again breaking the bond with the floor.
So I’m looking for some ideas as the the cause of the failure. Is the wooden floor system actually shrinking that much in the middle of the dry winter to break the bond from the tile and if so how should I resolve the issue? Will cement backer board solve the issue? Thanks for your thoughts.
Replies
I'm not trying to be Mr. Obvious but did you use porcelain tile?
It requires a different thinset or adding a special chemical to regular thinset.
If you don't, the tile won't bond.
I did use thinset with a hardening agent. I believe it was Latacrete 77
The tile is actually buckling in the air. They are popping up in patches, where two tiles are actually rising off the floor about an inch indicating that the wood flooring is definately shrinking and the tile has to rise to compensate. The thinset is on the tile breaking at the floor.
What is the isolation barrier that you refer too? Is it cement board or some sort of plastic layer. And, will a layer of 3/4 T&G along with a layer of 1/2" cement board be enough for mechanical strength. Thanks
Let me be clear. I'm a G.C. and not a tile guy but I will tell you how my tile sub does it and we've never had a problem.
We subfloor with 3/4" T&G Advantech. He then beds 1/2" cement backerboard (he prefers Hardi) into a scratchcoat of thinset mortar. It's screwed down every 6 or 8 inches in each direction. (I cannot remember if it's 6 or 8) He leaves maybe a 1/4" gap between pieces for expansion. The gaps are bridged with a special fiberglass like tape that resists getting eaten up by the thinset.
If memory serves me correctly he does the tape AS he's setting the tile but I might be wrong on that part.
The only reason I went Mr. Obvious on you in my previous post was that your problem sounded earily similar to something that happened on one of my houses with a prior tile sub. However, in your additional post you mentioned the thinset sticking to the tile. That did NOT happen in our case.
Our situation at first appeared to be bad grouting. When we went to grind out the old grout we found we could literally pick tiles up off the floor with NO thinset on them as if they were brand new.
My new tile sub figured it out right away.
That's just one of many reasons he's my guy now. (using sanded caulk between the tile and acrylic tubs instead of grout is another)
Your thinset has to be a mix that's "GOOD ON WOOD". Use a mister and pre-soak the plywood prior to putting down the thinset mix, and don't make the repair in the heating season as both of those things SUCK the moisture out of the thinset and it doesn't cure properly
That's not going to help him if the underlayment is improperly installed.
VERY true........
Your tile may be expanding as much as your floor is shrinking. You have not answered my question about temperature swing. Add humidity swing to the answer while you are at it.
How did you fasten the underlayment? I ststed in the last post the number of screws you should have, and you did not glue it down..........
You are obviously excited and are jumping all over to find an answer.
Calm down and approach this as a detective would to solve a mystery. There are MANY factors at work here, NONE of which can be discounted.
Go to Schluter.com and look for Ditra. One form of many for isolation membrane.
You want to educate yourself till your dizzy before you do this floor again.
Breathe...........
The room temperature is always 70 degrees. The 1/2 CDX is screwed about every 6"
I believe that water or floor temp is important here. 140 as you stated earlier sounds high.
Is that what it takes to maintain 70 deg floor temp?
If I was to do your floor over, I would contact the TCNA by phone and get a recommendation as well as one from the tile manufacture and a good heating contractor that has experience with these sysytems.
Try to find a common thread throughout the recommendations.
My guess is that the lack of glue under your underlayment combined with a possible lack of screws and no crack isolation membrane (google is your friend) is the cause of your troubles.
Try your ?'s at johnbridgeforums.net?
I've been over at the John Bridge tile forum reading some posts on "tenting", which is the name for what's occurring to your floor. Confusingly, it's also the term for what happens when you start screwing down the edges of a piece of ply and work toward the middle, but that could also be a factor in your tiles popping, as it were.The top dogs there recommend drilling 1/8" holes in the top layer of ply to let it suck down tightly to the 3/4" layer below, and the use of glue between layers, with stagggered joints. No shims in the joists below are allowed. You must leave expansion room around the perimeter...not even grout. And they like Ditra, a lot. If it's any comfort - and it won't be - this is a common problem, but mostly with slabs. Google "tenting" with "tile" .... too much info to put here. Much of it seems a mystery, in heated and unheated floors, with tiles popping years after installation even after being well adhered. One fellow said that a loud popping of tiles actually shows there was a solid connection. My interest is that i installed a similar structure to yours. The first tiles were laid with Versabond and did not stick. (They didn't tent like yours, just came loose.) I pulled them, ground the mortar off the backs, then relaid them with Mapei thinset. They're trouble-free now for 5-1/2 years...knock on wood.
To me anyone that thinsets tile to plywood is asking for it. I KNOW it CAN be done but so can a lot of things.........if ya wanna take chances cutting corners.
Even without predrilling holes b/4 you screw your plywood subfloors down shouldn't be a problem if you're adding a cbu or Ditra over it being you have to thinset that down. I know a LOT of people that don't thinset down the cbu's. they just screw it down which is WRONG. One also doesn't want to screw through the cbu into the joists which also can cause problems but one shouldn't be using CBU screws that long anyway.
I've always used PL375 subfloor adhesive between my 1/2" and 3/4" subfloor. One giant tube+ per board.
And adding a radiant heat system below is just REALLY asking for it without a cbu or Ditra.
I also agree that Advantech is probably THE best subfloor hands down but not absolutly necessary.
Gawd I'm happy I'llbe done next week...whewwwwwwwww
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I've been following that beautiful job you're doing. The dark trim really sets it off. I've twice had failures over ply, the other with a nasty Quickrete product that was also very sandy like the Versabond i used. I fixed that job with something called "Spec Mix", which i can't get it anymore. I'm using Mapei in my bathroom slate job now. I put some on the ply panel on the tub deck and the only way to remove it would be a chisel. Maybe five years from now it'll fall off voluntarily, though...job security. <G> I read a whole lot on the tenting phenom tonight and there seems to be a real problem there with no explanation, just stabs in the dark. Most of the cases have nothing to do with plywood, cracking, moisture, or RFH, in fact. The tiles can be fine for years, then suddenly start explosively popping for no discernible reason. Sometimes the thinset cleaves to the substrate only, sometimes to the tile only, and sometimes both conditions occur on the same floor. It's really a pretty fascinating failure when you look into it.
Never used Mapei but I know it's probably the best...and most expensive not that thats a consideration in a lot of cases.... all things considered.
You could really go over-kill and use Spectralock grout too if ya want. I never used that either but know that stuff also has to be the best.
I find Versabond a great all around thinset. I'm very happy with it.
Like I said to Eric....I can't see tiling right on top of ply. Makes no sence to me when we have so many great substrates thats made specifically for tile. Way I see it is...stone thinset(also stone) on stone(cbu) can't be beat. Makes for one solid unit which is seriously glued and screwed to death to the 1 1/4" of ply.
Yeh...the wood work I did does really set the whole thing off beautifully. I was real lucky to get the woodwork stain I mixed up to match the billion dollar vanity he bought being they're different woods. All the expensive fixtures they bought including the medicine chest I ended up having to assemble (grrrr) before installing really had my nerves creeping outta me...where's some zanex when ya need it?
Well...off to meet Sparky there now....ugh
ADVERT FOR VERSABOND...lol
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Edited 2/18/2009 8:00 am ET by andybuildz
In Bournemouth, England, i saw some enormous, intact, mosaic floors the Romans put down over radiant floor heating, as it were. There were three layers of the stuff - they'd "remodel" every 100 years or so with the latest designs - that were rediscovered when excavating for some new water lines. I'm pretty sure those guys didn't have Ditra. I know you're all agog with the stuff right now, but it's track record is still short, if promising. I remember Masonite siding and PB tubing...What i found interesting about the tenting issue was the fact that, although some failures might have been pilot error, others perfectly installed jobs over clean, level, dry CONCRETE slabs would suddenly fail spectacularly after many years of service. I'm talking explosive cracking that people described as gun reports, not rather obvious and immediate failures like mine from possibly getting a bad bag. I adored the Mapei products after my first bucket. I've use their white and grey thinsets, grout...it's lovely stuff. And i learned about it from old Gabe, my [former] nemesis, lol! As to price...i scored several of the big bags at Lowe's that some genius with a forklift ripped open. Lowe's put the ripped bags inside garbage bags and tagged them for $5. Right place at the right time...
In Bournemouth, England, i saw some enormous, intact, mosaic floors the Romans put down over radiant floor heating, as it were
I doubt they did it over plywood subfloors...lol....which was my main point.
Far as Ditra goes....I dunno, but I'm pretty confident with CBU's installed properly.
My point was that what you end up with using a good thick subfloor glued and screwed properly first and then using Cement boards and thinset and tile is basically a complete stone surface vs just tile thinset over a laminate (plywood).
It takes a lot to convince me of any product but I've been doing it this way with CBU's for decades and NEVER EVER had one tile fail on me so I'm purty convinced.
Far as Ditra....It makes sence to me and I've used it and like it but I can't say I know it's track record...so I won't claim to.
Same with Kerdi although Kerdi has me pretty convinced from a logical point of view besides a practical one........and I've used it alot.
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Edited 2/18/2009 5:30 pm ET by andybuildz
My first shower surround, 1985, i used white drywall and mastic with ceramic tiles - i didn't know any better and neither did the guy who sold me the stuff. Dang thing is still in use...i be a fanatical groutess.I was surprised in my googling last night to see that 3/4" ply on 16" centers met the John Bridge forums "deflecto" requirements. Wow...I realize i have no idea what the difference is between Kerdi and Ditra, since i thought they were just different brands. Back to my search engines...
"I realize i have no idea what the difference is between Kerdi and Ditra, since i thought they were just different brands. Back to my search engines..."
Kerdi is a poly membrane with a spun orange-colored "fleece" on each face of the poly. It's used on shower walls, tub surround walls, and shower floors. Pretty much just a waterproofing membrane.
Ditra is a waffle-type of material, about 1/8" thick. Pretty much just a floor membrane. By itself it's waterproof, you can make the whole floor waterproof by running a strip of Kerdi over the seams of the abutted lengths of Ditra. Ditra is also a crack isolation and uncoupling membrane.
Both made by Schluter.
View ImageABOVE: Kerdi on the shower floor.
View ImageABOVE: Ditra on a concrete slab.
I remember those photos from when you did your most excellent thread on the topic. I missed the distinction then bec i'd never seen a piece of it up close and personal, but i've seen it in Lowe's now and done some more googling for images and info so i'm squared away. I read some opposition to that drain like you installed, but no reason was given. I'm was thinking i should ask somebody about that, so since you're here....do you have any idea why it isn't universally appreciated as much as the membrane?
Who's griping about the drain? Is it over on the JB forums? I've never fielded a complaint from someone else, nor have I complained on my own. Setting the flange can be a little tricky, especially if you only have access from the shower itself (no access from below), which means you're glueing up the PVC/ABS and mudding in the flange in one step.As to the drain itself, I like the lateral as well as vertical adjustment.Personally I like it. I'm waiting for Kerdi Board to finally make it to market.
Well, i've spent a whole bunch of time looking on the JB forum - I think i've fallen in love with "CX" now - for the post i saw, but i was all over the Net when i was originally looking into tenting, so there's no telling where it was for sure. Reading a lot more in particular about Kerdi + drain shows me that it baffles a few folks...one guy used a layer of Kerdi between two layers of mud...but there certainly aren't any wholesale objections.
All these years and the only tenting I get is in me trousers....hahahahaha
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Like the fellow said, 140º is too hot.
I'm an extremeist...so sue me : )~
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I thought splintergroupie would ask "front or back?"
Billy
I think she's not only dbl jointed but ambidextrous as well....multi talented...the possiblities are endless...its haunting
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Why do I keep...http://www.youtube.com/watch?v=n7ZkQC0riwc
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whats the deal with 'cx'...tells you to use your first name and he goes by the name 'cx'?...weird
Yeah, that's strange. I'd still be a CX fan if i found out his name was Fred, but i would no longer want to have his children. A little mystery is a good thing. <G>
Ask CX about searching for owls. It might add more mystery than it answers!
He is a great guy and there are a lot of good folks over there.
Billy
Does your fascination with him has to do with that unfulfilled yearning you have for living in 19th century London?<g>
But...i got the impression he was a younger man than that....? He has just a hair less than a million posts on there. Not a difficult achievement, for sure, except that his are all literate and logical. I'm dying to get my independent clause on him, except for the fact he's armed and dangerous.
The Romans I believe set tile over thick beds of sand... which serves as a decoupling layer.i.e. essentially the principal behind Ditra.
And a lot of it was still "tented"! ;^)
(I mistook the name of place; it was Fishbourne, not Bournemouth.)
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50lbs of Mapei Full Flex is just about $25.00 inc tax.
Just about the same as any other including Versa. Try it sometime.
Only reason I haven't is cuz no one close by sells it. Thats the only reason.
And yeh...thats the same price as Versabond
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Andy,
The job looks great! Try to get SOME thinset on the tiles next time though. I mean, how much do those pants weigh by now?
Thinset on ply............it's NEVER been about cutting corners. We use to use an epoxy mortar, then they had us add 'milk' to the thinset. Now it's in the thinset. TCNA even has specs on the install and they don't use a CI membrane. Done correctly, it's done well.
Like I said..I know you can tile on ply. I've done demo on bathrooms with the ply stuck unbelievably well to the tile but in my mind it hasn't anything to do with it sticking (to the top layer of a wood substrate). It has to do with ply moving or possibly delaminating in "some cases". The added assurance of a substrate thats not going to move near as much like cbu or Ditra ...especially separating it from the ply just makes me feel MUCH more comfortable. I mean you don't need Kerdi in a shower either...ya know? It's just better for obvious reasons. Different circumstances in different conditions cause all kinda different problems that we're unaware of b/4 hand...like leaks from a tub, sink or shower that get behind the tile....like radiant heat doing who knows what beneath the ply....etc etc
Look at Splinties post where she talks about all the issues she's reading about that go pretty much unexplained with tenting and the such.
I always say better safe then sorry. I've NEVER had one single tile ever lift. Maybe thats why all my work stays solid as a rock. I always go for over-kill...probably because of some low self esteem issue....lol. Never confident in what I do is gonna work out.....even after over 3 decades.
Those cargo pants are amazing. I put them in the wash and they come out clean as new no matter what gets on them. That was mostly grout you see on em from sliding around the floors and up the walls...lol. Has that rip stop fabric too. i specifically bought them for tiling work.
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Edited 2/18/2009 8:03 am ET by andybuildz
Good call SP. I'm sure the info you provided will be helpfull to the OP.
You can't beat Mapei products.
If your joists are 16" on center you should be ok deflection-wise.
I understand your description of the construct, the tiles are laid on the plywood and the radiant is underneath the sub floor......
I don't believe modified thinset alone will solve your problems. IMHO, you need to demo and add a decoupling layer between the sub floor and the tile.
Nobel(CIS) and Schluter(Ditra) make thin membranes that come on a roll. A layer of 1/4" cement board on top of the sub floor is another time tested alternative.
Good luck
The awful thing is that beauty is mysterious as well as terrible. God and the devil are fighting there, and the battlefield is the heart of man.
- Fyodor Dostoyevski
I installed tile over plywood for a long time before they came up with some of today's alternatives, and never had a problem...ever!!
I always glued the top layer of plywood to the bottom layer of ply with a full bed of adhesive. This, in effect, gave you a solid 1 1/4" of plywood under the tile.
I would bet that you just have the 1/2" screwed to the 3/4". I think what you are seeing is the ply absorbing moisture in the offseason and drying out drastically during the heating cycle. Your 2x12's are doing the same thing.
I would suspect there is plywood buckling and not enough actual solid support for the tile ( especially if it is large tile) Check to see if the 3/4" subfloor shows separation from the 2x12 when this is happening.
I'm not sure even Ditra would handle this problem alone. I would rip off the tile, the 1/2" ply and screw the 3/4" back down with lots of screws. Then install 1/2"cement board in a solid base of thinset. (modified)
Then install Ditra for good measure, and re- lay the tile.
That's correct, the 1/2" is only screwed to the 3/4" base plywood. You would be comfortable removing the 1/2" CDX and relying on the 3/4" and the cement board for support? You've successfully installed this scenerio before?
The radiant water temperature is about 140 dergrees F.
Thanks
That's correct, the 1/2" is only screwed to the 3/4" base plywood. You would be comfortable removing the 1/2" CDX and relying on the 3/4" and the cement board for support? You've successfully installed this scenerio before? Yes, dozens of times in remodeling jobs. It sounds like you shouldn't have a span issue with the 2x12s. Is your floor springy? You may also have some poor grade plywood. If it's SYP, that's very bad. The stuff shrinks, swells, bends like crazy with changes in moisture content. Be sure to bond the 1/2" cement board to the subfloor with a full bed of thinset. As others have said, Mapei is my favorite...great stuff.
If your tile are rather large, you may not be getting enough mortar on the tile either. Nothing will stick tho' if the plywood is buckling. The less wood you have under tile, the better as long as your floor is stiff enough. Do exactly what I told you, and the problem should go away.
The radiant water temperature is about 140 dergrees F. That's very hot for underfloor heat using aluminum plates. You are probably baking everything with temperatures like that. Eliminating one layer of plywood will help your heat transfer too, allowing you to use lower temp water.
What Mapei product do you recommend for the installation? Is it thin set or is it some sort of plastic de-coupling layer? So you recommend that I remove the 1/2" CDX from the floor, replace it with cement board that's attached with screws and thin set. Next, the tile will be applied to the cement board with the Mapie thin set and the use of some sort of plastic de-coupling layer? Just want to get it straight. Thanks for the help.
Here's what I would do in your situation:
Tear up the tile and the 1/2" plywood.
Screw the entire field of 3/4" subfloor to the floor joists.
Since you probably need to replace the 1/2" thick plywood for height reasons, I would use 1/2" Durock bedded into modified thinset & screwed down. This will definitely stiffen your floor and will also help transfer the heat evenly throughout the floor. Technically, you could get away without using the 1/2" cement board if you use something like Ditra under the tile, but in this scenario, I'd use the Durock too.
I would use Ditra as the uncoupling membrane. You would have to use it in either scenario. It's expensive, but it's a very good product. Tile floors over radiant heat should always have an uncoupling membrane under them. You would use unmodified thinset both under and over the Ditra if you use the cement board.
I just like the working characteristics of Mapei thinset. You would need both modified & unmodified (standard) types.
3/4" subfloor > 1/2" Durock > Ditra > Tile
OH, and lower the water temperature in the heat tubes. There's no reason for 140 water. 120-125 should work fine if the joist space under the tubes is well insulated.
Edited 2/25/2009 10:45 pm ET by BoJangles
Edited 2/25/2009 10:48 pm ET by BoJangles
What is your water temp? What are your burner/RFH controls? What is your programed max floor temp?
My best guess is that your underlayment and your tile are expanding and contracting at different rates and that has caused you tile to come un done.
I don't know that the fact that you did not glue the 1/2" down has played into this.........I always glue and screw. Usually pour yellow carpenters glue all over the subfloor then set the underlayment on top and screw away. I could be movw mwnt of the underlayment. You should have at least 100 screws in a full sheet of ply.
Figure 8 screws x 6 joists and then two rows of 8 screws each in between each set of joists.
A decoupling membrane is probably the key here. It provides a buffer between the different expansion rates of the materials.
Has the floor experienced wild swings in temperatures. IE, do you leave the house cold then slam on the heat?
How has the tile come up, is the thinset still stuck to the tile or the underlayment?
I'll look up TCA specs for you. Give me a little time.
The obvious question just ocurred to me...........did you gap or space your underlayment?
TCNA hand book does not cover staple up hydronic.
I did leave about an 1/8" gap between the sheets of 1/2" CDX
We have had a similar problem with a new build so this article is interesting to me. Our sub used approx 1/2" self leveling mortar on top of 3/4" subfloor. He set the electric heat mats on the subfloor, poured the self leveling mortar, added thinset and set the mosaic tiles. Both bathrooms were done the same and both had tiles buckle at the same time - in the winter after the humidy dropped significantly. The tiles have been reset in the thinset but I'm not convinced the problem is solved.
TCNA recomends a crack isolation membrane over the SLC.
I believe that alot of these tile over heat installs are simply problematic no matter what.
agreed. the crack isolation membrane wasn't used - it should have been used and I still don't know why the sub didn't use it. It is relatively easy to remove the tiles and lay the membrane...would you use a flexible thinset?
Thank you
You still need to address your underlayment issue.
Read on...........
rip it up & do a mud job never have a problem again or at least add tar paper & stucco mesh w/ a good quality flex bond thinset
no question, the tiles are coming out and will be done over. i'm convinced the sub did not use the correct thinset and also did not allow for any movement. The hexagon tiles did "tent" which made it obvious to me of the errors made.
appreciate the feeback from you and Eric - thank you.
Eric,
Curious if you or anyone else has used LATICRETE¯ Sound & Crack Adhesive as a flexible thinset in place of crack isolation membrane or in combination with. We use their SpectraLock epoxy grout always but have yet to try the sound & crack adhesive.
I'm not sure what that is, probably never used it. latticrete make fine products. Mapei has the market in this area mostly so that is what I use.
Have you ventured over to John Bridge forums? And look into the Schluter products. Ditra is what you want to look for.
There is a distributor in Buffalo NY that ship and has good prices.
yes, they too have been helpful at the John Bridge forums. thanks Eric.
Reminders:
You MUST have a minimum of (2) layers of 19/32" plywood down BEFORE your CBUs. A layer of 3/4" ply under the CBUs isn't adequate. The CBUs must be mortared down.
Schluter Ditra or similar is nice with tile floors ... but REQUIRED when you have radiant heating (not optional).
Finally, you may or may not be aware that grout could be part of the problem since around the time you mentioned (16 years = 1993) there was some bad grout on the market.
Jeff
Reminders:You MUST have a minimum of (2) layers of 19/32" plywood down BEFORE your CBUs. A layer of 3/4" ply under the CBUs isn't adequate. The CBUs must be mortared down.
See pg 40 of the TCNA 2008 handbook. 1/2" cbu over 5/8" t&g (19/32") plywood.
You handing out stepladders for thresholds?
I happen to agree with Jeff. It's a bit of overkill but not THAT much. I like dbl 3/4" when possible. As for the threshold I don't put my saddles ontop I cut one of the beveled edges off and butt it to the tile height. Most saddles I find are 1/2" which is perfect. In fact I'm going over to tie up the bathroom I'm finishing this week and giving that saddle a coat of poly.
Also CBU's don't add strength to the deflection of a floor for tile. I do think it helps but it's nothing I count into the equation...it's just gravey IMO..
Also...when possible I love using Advantech for my subfloors..although I hate carrying it and cutting it....can't have everything : )
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Also CBU's don't add strength to the deflection of a floor for tile. I do think it helps but it's nothing I count into the equation...it's just gravey IMO..
You're contradicting yourself aren't you? I agree that the CBU layer is not actually rated as a structural member, but a layer bedded in thinset certainly does stiffen the floor. How much, I don't know, but if you use this method you can tell it definitely adds to the stiffness of the floor.
Like you, I like to start out right at the beginning in new homes. Very stiff I-Joists with Advantech screwed and glued. If you do that right, you don't need any more wood on top.
The less wood, the better, when it comes to heat tubes under the floor.
You're contradicting yourself aren't you? I agree that the CBU layer is not actually rated as a structural member, but a layer bedded in thinset certainly does stiffen the floor. How much, I don't know
How am I contradicting myself? Like I said....if it does anything to add to the integrity I count it as gravy....but I won't count on it to do that. It's brittle unlike plywood or Advantech. I mean every little thing does help but I won't add it into the equation in my figuring of adding to the integrity of the floors delection. Then again don't go by me b/c I usually shoot for a bit of overkill and worry far too much about every little detail...ugh View Image
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It's not overkill - it's TCNA Manual.
Jeff
It's not overkill - it's TCNA Manual
You had better doublecheck that statement. It's not in any manual I've seen.
Eric is right on this matter.
Edited 2/26/2009 12:42 pm ET by BoJangles
Reference is to TCNA Manual Detail F144-05, F170-05 etc.
Jeff
Edited 2/26/2009 12:53 pm ET by Jeff_Clarke
Reference is to TCNA Manual Detail F144-05, F170-05 etc.
That is a 20-(05) edition you are quoting from. Those manuals specify how to install tile over different types of floor situations. The example you give is one type of floor. It does not mean that is the only way to install tile over a wood floor. If you keep reading, you will probably find the section(s) Eric is referring to and how to properly install tile without using two layers of plywood....which is basically an obsolete process in new home construction.
I probably installed tens of thousands of square feet of tile over two layers of plywood, but I wouldn't do it today. For one thing, the quality of plywood has gotten dramatically worse over the years and in my opinion has become an unreliable base for a tile floor. Advantech is a much superior product for subflooring under tile if you have to use a wood subfloor.
Jeff...first off I was agreeing with you about using dbl 3/4" ply but it IS overkill.
Specs I believe are 1 1/8" minimum but most people that do it right use 3/4 and 1/2" screwed and glued. Thats "usually" how I do it and then put either 1/2" or 1/4" Hardie over that...thinset and screwed to death but in a lot of questionable cases I just go for dbl 3/4" if the height isn't really an issue and like I said...I cut the bevel off any saddle and butt the tile or make my own saddles.
BTW...I've been debated about this but....I believe that the 3/4" ply must go down first over the floor joists and the 1/2" glued and screwed to that.
As I said in my previous post way back in this thread...and others agree is that T&G Advantech is the best possible substrate out there! Just kinda sucks workin' with IMO...oh well.
http://www.cliffordrenovations.com
http://www.ramdass.org
Edited 2/26/2009 5:05 pm ET by andybuildz
I didn't say double 3/4" ply. I said double 19/32" ply before CBU. That's what the TCNA details show. That = 1 1/8" plywood. I don't think that the extra 3/8" over 3/4" ply thickness generally requires a stepladder, unless you're an ant.
Jeff
with your system you are close to 3/4 higher than the finish wood floor already and that is with out tile. You could easily see an inch or more.
Not something I would wish to live with if there were a reasonable alternative.
whoops...my mistake...but you ARE correct....I agreed either way... 1 1/8 or even dbl 3/4"....either way you don't need a step ladder. It all depends on the situation.
Nothing is written in stone...so to speak..lol.
It's pretty much all common sense once you know the minimum and what the situation at hand allows.
For the most part I just about always go 3/4 + 1/2 plus my CBU....usually I do 1/2" Hardie...if I go dbl 3/4 I go w/ 1/4" Hardie.....
Lately I cut all my Hardie outside b/4 bringing it in with my grinder. What a breeze!!!!
http://www.cliffordrenovations.com
http://www.ramdass.org
Which F- detail are you quoting - I don't have the 2008 book yet.
Jeff
Actually it's om page 39.
F144-07
I don't see any structures indicating an isolation membrane over cbu. I'm not sure I would bother. But then the book does not show and underfloor radiant systems at all.
Though I am not a big fan of either Byrnes or the TCNA book, I will quote MB from a recent JLC thread. He says the TCNA book is a bare minimum of standards.
I've done a hundred or so jobs over double plywood and thinset. The good stuff made to stick to plywood. It's formulated to do just that; stick. I've done a couple of jobs with CBU over a single layer of ply-architect spec'd so I'm off the hook. Came out awesome.
I would consider double ply with cbu (not to mention a membrane) a total waste of time and materials.
Just my opinion, and you know what they say about those!
Make sure the 1/2" layer is well secured (sounds like it if it is screwed every 6"), use Ditra uncoupling membrane, and lay the ditra and the tile with Ditraset25, if you can find it at your local supplier. Make sure you follow directions exactly.
It's made by Bostik and is formulated especially for use with ditra.
I'm surprised no one at John Bridge asked you this -- what kind of expansion gap do you have around the perimter of your tiles? You didn't cut them tight to the wall, or grout them to the baseboard, did you?
Tenting is usually caused by the lack of expansion gaps around the perimeter (or the lack of periodic expansion gaps in large commercial areas). The tile expands with the heated floor and it has no expansion gap, the only place it can expand is upward, and the tenting usually happens in the center of the floor.
Perhaps in your case it has something to do with the wood shrinking as well.
Ditto what everyone else said about using Ditra or cement board under the tile. And get rid of the CDX if you can and use a better grade of 1/2" ply.
Billy
Thanks for the info thus far. I left a saw kerf of expansion around the parameter of the CDX. The floor was installed about 16 years ago so I can’t remember if I left an expansion gap around the parameter of the ceramic tile layer. The tenting did appear in the center of the floor. One posting referred to the replacement of the ½” layer with cement board and using Ditra. They tell me that the 1/2” cement board would be enough support over the ¾” T&G plywood, only because I’d like to keep the floor thickness to a minimum since the radiant heat needs to conduct through the floor to heat the space above. Previous posts have suggested that I thinset the ½” cement board to the ¾” plywood. Where would the Ditra be installed, above the cement board or below? Again thanks for the help, not sure where to turn on this one. Thanks, Matt
Ditra's used "instead" of cement boards.
http://www.cliffordrenovations.com
Why do I keep...http://www.youtube.com/watch?v=n7ZkQC0riwc
http://www.ramdass.org
Matt,
One way to tell if you left an expansion gap is to pull off some baseboard and check if there is a gap between the tile and wall (the bottom plate if it is a stud wall). This assumes you put baseboard over the tile.
If you installed the tile hard against the walls OR grouted between the tile and the walls, this could cause the tenting.
1/2 inch cement board provides absolutely no structural support. If you have a 3/4" subfloor you need another 1/2" of plywood and then EITHER cement board (thinsetted and screwed down) OR Ditra before you set the tile.
I hope this helps.
Billy
I installed a radiant heat system (electric) in my bathroom 5+ years ago - laid down a double layer of Durock to isolate the heating pad from the sub-floor. I've had no problems with the 14" tiles peeling despite daily heat / cool cycles, and the floor is stiff as....