Correct way to install tile?

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Old 10-08-10, 06:59 AM
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Correct way to install tile?

I am new to the site but have had many years of watching and assisting relative diy'ers remodel their homes. I do not claim any professional knowledge. I am now in the midst of (finally) doing work in my own home but do not have the luxury of having the assistance of all those relatives that I helped in previous years. I have been reading the site for research purposes and have come across a lot of information and comments about the correct installation of tile. I'm feeling very confused about the constant recommendation of "cement" board (I recall the term being "durarock", now it's "hardibacker"). All, and I mean ALL the contractors I talk to don't use the cement board. They lay the tile on wood/plywood/whatever the width. I even asked specifically about it when I wanted my bathroom floor redone and the guy scoffed and wanted to know why I asked "because you only need that when you're putting tiles on the wall". Needless to say, he wasn't hired. We had tile put in along with carpet (different company) and they just layed down a sheet of plywood and put the tile on it. It's 2 rows of tile in front of a slider so it doesn't get traffic or anything set on it. I was not present when the previous bathroom was put it but eyeballing it, it looks to be the same height so I doubt any extra board was used. The flooring in the home is some sort of 'cement' type board. I saw it when they pulled the old carpet out and it kicked up quite a bit of dust. I couldn't identify it, the place was built in the early 80's. My concern is if all these installations were done "incorrectly", by "professionals" no less, how long will it last? And does anyone know what kind of subfloor this is? Is it an acceptable subfloor to put tile directly on? The original tile in the bathroom seems to solid and it's been 30 years. I'm still semi debating whether to redo the tile. Right now, I'm just going to try to clean it but it that doesn't work, I'm not sure what I'll do. The tile are those itty bitty ones and it's going to be a bear to remove and replace grout. We won't be here forever but I am not one to just do something cheaply just to sell and leave the next person with a headache. Any information or ideas would be helpful.
 
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Old 10-08-10, 09:42 AM
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Oldmada,

You've said a whole lot here, so I'll do what I can to answer some of your questions.

There are considered two proper ways to install floor tile, neither includes installing directly over plywood.

Your first consideration has to be your subfloor. Plywood is never considered an acceptable substrate material for tile or stone, if you're adding a product which has water in it, and we all knkow what happens to wood when it is exposed to water. Also consider that grout is porous and will allow water to penetrate through your joints, which will further expose the wood to damage. The industry term for "cement board" is Cementious Backer Unit, or CBU. Durock and Hardibacker are two types of this. They offer the necessary compression strength and minimize the effects of deflection inherent in residential subfloors.

The reason many "professionals" are okay with setting tile over plywood is that Luan plywood was at one time considered an acceptable material for tile installations, however, it no longer is.

AMERICAN NATIONAL STANDARD SPECIFICATIONS FOR THE INSTALLATION OF CERAMIC TILE (ANSI-1999) ANSI A 108 Page 13
AN-2.4.3 CAUTION: Wood-based panels such as particle board, composite panels (veneer faces bonded to reconstituted wood cores), luan plywood and soft wood plywood all expand and contract with changes in moisture content and are not recommended as backing materials for ceramic tile...


The other method for installing tile is a mud-set floor, which is honestly beyond the scope and ability of the vast majority of DIYers, so I won't get into it here.

As for how long your floor will last that is hard to say. There is no exact science to when an improper install will fail, but rest assured it will. It is likely you won't get 5 years out of it, and I would say you have a ceiling of 10 years or so, long enough so any warranty implied by the contractor will expire.

As a side note, if the original tile is 30 years old, I would almost guarantee that it was mud-set with drypack. Especially if the tiles are 1"x1" as this was the standard method of install for many years. The vast majority of tile floors predating the 80s were set with this method, and can and will last in excess of 50 years with no major failures.

If you are looking for an easy way to remove and repair grout, I recommend the new dremel multimax with a diamond blade on it, it will not damage tiles should you slip and gives you some measure of precision for removing grout from joints. The other method is to use a diamond blade on a 4" angle grinder. I would caution against this method, as one slip can cut into your tiles and make a small project much worse.

As for cleaning, I would attempt an acid wash with muriatic acid. it's likely that your grout isn't properly grout, but a portland cement/sand mix. Modern grouts are very different from those used even 20 years ago. if this is the case scrubbing with rubber gloves on with a 3 to 1 diluted mix of muriatic acid, leave sit for 5 minutes and wash with clean water 2-3 times to remove residue. If this doesn't clean it, nothing you can do will.

A caution regarding muriatic acid, it is very caustic, and it typically the last resort of a professional tile installer. Do not store it/get it on anything metal as it will corrode metal very quickly. keep it off of exposed skin as it will cause rather bad chemical burns. Safety information is always on the bottle and I would recommend reading and following it. ventilation is very important as well. You can buy it at pretty much any home improvement store.
 
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Old 10-08-10, 10:45 AM
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You can set tile directly to plywood. I believe its (TCNA) F150-05. It requires 2 layers of plywood, a minimum 5/8" t&g plywood subfloor and another layer of 5/8" exterior glue plywood with 1/8" gap between the sheets. This is not normally a method that we suggest hear because it has a high failure rate if everything is not done just right. Many (not all) so called pro's that set on plywood don't know how to do it right. Diyer's typically have much better results with cement board or isolation membranes over plywood.

I agree with what Shotty said about your existing tile. Most likely a mud job that'll last a life time. If it was set on plywood, you have evidence of problems by now.
 
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Old 10-08-10, 11:15 AM
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Originally Posted by HeresJohnny View Post
You can set tile directly to plywood. I believe its (TCNA) F150-05. It requires 2 layers of plywood, a minimum 5/8" t&g plywood subfloor and another layer of 5/8" exterior glue plywood with 1/8" gap between the sheets. This is not normally a method that we suggest hear because it has a high failure rate if everything is not done just right. Many (not all) so called pro's that set on plywood don't know how to do it right. Diyer's typically have much better results with cement board or isolation membranes over plywood.
I agree with what Shotty said about your existing tile. Most likely a mud job that'll last a life time. If it was set on plywood, you have evidence of problems by now.
I hate to veer off topic , but I wanted to note that while HeresJohnny is correct, it has always intrigued me that the appTCNA and ANSI standards differ so greatly here. While I understand the whole floating floor concept behind two separate plywood boards, it makes me wonder why the TCNA continues to approve it since it opens the door to so much misinformation...
 
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Old 10-08-10, 11:55 AM
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I'm not a tile pro and I'll take my beating from the guys that do it for a living - but here goes. Nearly twenty five years ago I tiled a bath, hallway and kitchen. I had never tiled anything more than a vanity top at the time so I bought a book.

That book provided different methods of laying tile. One of them was using mastic directly on plywood. Being ignorant of the right way to do things, that's the method I chose. I ripped up the kitchen and hallway 5 years ago as part of a kitchen reno. It was a real PITA. In some areas I had to remove part of the subfloor because the tile was so stubborn. There was not a single cracked or loose tile nor any cracked grout. A month ago I ripped up the bathroom tile as part of a reno. Same story. Maybe your guys read the same book?

If it's 30 years old and not showing damage I wouldn't lose any sleep over it. However, with that said, when I retiled my master bath a few years ago I used Hardibacker. Hardibacker and Durock are brand names the generic name I see most used for cement backer board is CBU. There are newer products (membranes) on the market that may be used instead of CBU. When I tile the bath I'm working on now I will probably use a product called EasyMat.
 
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Old 10-08-10, 03:42 PM
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Wayne,

What you're talking about is not unheard of. Keep in mind that it's most common to see in areas of the country with no freeze thaw cycle, as well as with older homes. The reason for this is that there tends to be no movement. In the case of freeze thaw it's the introduction of water, and with older homes due to the fact that they have stopped settling.

It's also seen in areas where there are no basements or foundations are set on stone or very solid bedrock.

That said, I wouldn't count on it. In most installs a DIYer will do the work themselves to save money and put in a product that's a little more costly for a more high end look. If the install fails, which is very very likely, it will end up costing even more money.
 
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Old 10-09-10, 01:43 PM
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Thanks for the information. It is greatly appreciated. I had not heard of the acid wash but will look into it. I have some misgivings about it since I have a toddler running around and will have to plan a safe way to do it. I did read about using oxygen bleach on the grout and I figured it was a cheap option to try first since it would be safer. I had a chance to look up the mud set method and since it is a different composition than the more recent grout, I wonder if it would get the same results.

Regarding whether to redo the grout, it would be my last option since from what everyone has said, it is structurally sound with no cracks and will probably last for a long time. The other bathroom had been retiled because there was a soft spot under/near the toilet and there was a question about the structure.

There is some grout that is directly next to the shower/bath that I was able to scrape out and I can attribute it to dripping washcloths laid on the side of the tub. The floor is still solid as far as I can tell. Any suggestions on how to replace that area? I had thought of just mixing some grout from a small tile repair kit and filling it in. What about silicone calking? Calk on the floor wouldn't be very esthetically pleasing, though. Any suggestions?

One other issue is a marble thresh hold that is 4 inches wide. It has a crack in it. I would like to replace it with another marble piece but if there is an issue with cracking, how can it be prevented? And it's right next to the nice, solid, 30 year old tile.
 
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Old 10-09-10, 04:51 PM
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Originally Posted by Shotty View Post
Wayne,

What you're talking about is not unheard of. Keep in mind that it's most common to see in areas of the country with no freeze thaw cycle, as well as with older homes. The reason for this is that there tends to be no movement. In the case of freeze thaw it's the introduction of water, and with older homes due to the fact that they have stopped settling.

It's also seen in areas where there are no basements or foundations are set on stone or very solid bedrock.

That said, I wouldn't count on it. In most installs a DIYer will do the work themselves to save money and put in a product that's a little more costly for a more high end look. If the install fails, which is very very likely, it will end up costing even more money.
And this is where I always get stuck - why are you convinced that it is "very very likely" to fail? I believe that tile put down on a properly laid plywood subfloor and underlayment over adequate joist support is no more likely to fail tile lain over CBU. Olmada has a 30 y/o floor put down that way, mine was 20 + and a poster in another thread I just read also has had long time success with tile directly on plywood. I'm not saying that it's the best method, all I'm saying is that if done correctly it will be fine.
 
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Old 10-09-10, 08:35 PM
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Originally Posted by Wayne Mitchell View Post
And this is where I always get stuck - why are you convinced that it is "very very likely" to fail? I believe that tile put down on a properly laid plywood subfloor and underlayment over adequate joist support is no more likely to fail tile lain over CBU. Olmada has a 30 y/o floor put down that way, mine was 20 + and a poster in another thread I just read also has had long time success with tile directly on plywood. I'm not saying that it's the best method, all I'm saying is that if done correctly it will be fine.
Wayne,

I am very very convinced that it will fail because I have seen more floors laid in this method than I can recall which have failed. I have repaired many, at great cost.

Your assertion that plywood is no different than CBU is incorrect for one primary reason. Moisture. Wood reacts differently to the introduction of water than concrete does. All CBUs are in some way cement based, therefore are not subject to expansion/contraction. If a floor moves under the tile, the tile on top of it will move. This is why you use thinset under a CBU, if there is movement in the subfloor the thinset will typically break loose in whatever areas are necessary to maintain the integrity of the install.

As to Olmada's 30 year old floor, it was not installed in this method, I guarantee it. It was a mud set floor, meaning that it was floated with drypack mud (sand, portland cement, and water mixed to be the consistency of wet sand) and the tiles were likely fresh-set into this, meaning they were beat in with a wood block using pure portland cement as a bonding agent. This was the method used at the time the floor was installed, especially for 1x1 floor tile.

I'm not saying a floor laid in this way can't hold up, I'm saying it's a needle in a haystack. Not only is it not the best method, but it is absolutely not recommended to ever lay tile directly on a subfloor. You may have the word of another poster and one example of it working out OK, but my information is backed by the TCNA and ANSI standards which I would say are more likely to yield good advice about how to properly install a long lasting tile floor than a few examples and a gut feeling. You're entitled to believe whatever you like, as am I. My point is that while I'm paid very well to install tile for a living, there are people paid much more than me who say that you simply don't do it, based on tests repeated in a laboratory setting and repeated time and time again.
 
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Old 10-10-10, 08:53 AM
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i did my MIL's bathroom over 10 years ago. before i had the resources of this internet.

joist, 1x6 planks, treated plywood , tile. it still looks fine.

but, i would not do it that way again. i now know better.
 
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Old 10-10-10, 11:09 AM
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I'd like to add to the discussion about the differences between the mud set and the current style of installation. I'm in a condo on the second floor. And the subfloor is, and I'm saying this based on what I saw when the carpet was installed, I'm pretty sure some sort of cement board. I would also say this because the code probably requires a more fire retardent material between condos rather than just plywood. So, can I guess correctly that because it is this way, that it has helped the tile stand up to that many years? The fact that it's on a second floor protects it from a freeze-thaw effect and the subfloor is probably some sort of cement type material. Are these discussion points worthy of noting?
 
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Old 10-10-10, 04:51 PM
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Actually it is an important distinction. If you're building is a concrete/gypcrete slab, then no underlayment is necessary, you can install tile right over it. In some cases an anti fracture membrane is used to isolate cracks and the like, but no true "underlayment" is needed
 
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Old 10-10-10, 05:19 PM
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Well I will chime in and tell you my experience

My house was built in 1986 and about 12 years ago during my kitchen renovation I removed the linoleum from the floor and using thinset I glue right on the existing plywood 10x10 ceramics.

Today these ceramics look like new with no cracks
 
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Old 10-11-10, 07:06 AM
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Shotty,

Could you please explain "anti fracture membrane" to isolate cracks. This is even more frustrating since the tile could have been put right on it but then a layer of plywood was used. I wish that I could see what kind of effect that could have in later years. There is a small round area right outside the bathroom that was crumbly and in little pieces and there was a little bit of a depression when you walked there. I never knew why until the carpet was installed. All the carpeting guys did was shove a bunch of padding in the area. It's also the area right in front of the marble threshold that is cracked so I'm wondering if the instability affected it. Is there a way to 'repair' the slab you speak of? If the floor isn't stable in that particular spot, is there any point since it's a condo, (I don't want to go to much deeper in the structure). If it is the concrete slab, what's holding it and why would it be crumbly? Could I use some sort of a cement patch?
 
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Old 10-11-10, 07:53 AM
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Originally Posted by Shotty View Post
Wayne,

I am very very convinced that it will fail because I have seen more floors laid in this method than I can recall which have failed. I have repaired many, at great cost.

Your assertion that plywood is no different than CBU is incorrect for one primary reason. Moisture. Wood reacts differently to the introduction of water than concrete does. All CBUs are in some way cement based, therefore are not subject to expansion/contraction. If a floor moves under the tile, the tile on top of it will move. This is why you use thinset under a CBU, if there is movement in the subfloor the thinset will typically break loose in whatever areas are necessary to maintain the integrity of the install............
Sorry but Im with Wayne Mitchell on this subject.

True the plywood will absorb moisture but eventually it will dry out and it will be fine. All my tile jobs have been done straight on plywood and never had a problem. That includes my 25 years old place which is close by and visit often and all floors are perfect.

My opinion is that some jobs will fail not because the tile was set straight on plywood but for other reasons like no proper glue, not enough glue or the glue was half dry when the tile was put on.
 
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Old 10-11-10, 11:36 AM
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Oldmada,

Yes you could repair the slab if that's indeed what has happened. I've never heard of a slap crumbling in specific spots, though I'm sure it could if it was poured poorly. You could use pretty much any form of concrete patch to fill it in. Depending on how deep it is, you could possible flash it off with thinset or use a self levelling concrete as well. The latter two aren't recommended for anything requiring real depth, however.

A lot depends on what you're working with as the lowest layer in your substrate. If it is indeed a slab, it should be a very easy fix. If it's something else, especially a rotted out subfloor, it's a bigger fix. If you could post a picture of it, I could give you a much better idea of what you're working with and how to go about fixing it. If you're interested in talking to me, send me a private message and I'll give you my pohone number so we can have a discussion about it.
 
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Old 10-11-10, 11:44 AM
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Kolias,

You're welcome to stand with Wayne. I'm really not trying to convince anyone of anything. Wayne stated in his initial post that he was not a professional installer and wanted to discuss the issue. I am a professional installer, though admittedly I do a lot less residential work than I used to, as I am a union tilesetter, and the vast majority of my work is on very large commercial developments, hospitals, casinos, condos, and hotels.

The simple fact is that due to the nature of wood, especially plywood, when it gets wet and dries it warps. This means that whatever is on top of it will move with it. Thinset, when it gets old, has a tendency to get brittle, meaning your entire install is at risk of delaminating from your subfloor. If you used some form of "glue" or organic adhesive, there will be some amount of flexure in it due to it's very nature, however, these products are not recommended by the manufacturer for setting over plywood, nor is it typically spec'd that way by a designer.

Movement in the subfloor is the #1 cause of installation failure, regardless of coverage of adhesive/thinset, etc. I'm curious when you say all your tile jobs, how many are you referring to. I'd also be curious to know exactally what typr of plywood you're setting on, and what type of glue you are using, these are all important ingredients in the mix.
 
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Old 10-11-10, 02:43 PM
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Oldmada

If you are in a condo, you likely do not have a concrete slab, but rather gypcrete. I've seen this stuff in many condos. This stuff is real unstable and should not be tile over directly. Most condo associations will not let you remove this stuff, as it was put there for its sound isolation qualities.

Without going back to read this entire thread, starting from the bottom up, what is the composition of this floor? I'm confused, as there is discussion of a concrete slab, plywood, cement board.
 
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Old 10-11-10, 02:59 PM
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HeresJohnny,

Just to catch you up. I believe it is either a slab or gypcrete, though I disagree about installing over gypcrete. We do it on our jobs, though it is sealed prior to install. The only catch is when it is poured in a post tension system, as it doesn't have enough shear strength to hold up to high tension.

There was an issue with some crumbling of the substrate material, which the carpet layers filled with carpet pad. Evidently the substrate is crumbling, which I think could be due to air in the pour or a shear somewhere in the slab where it has gone unnoticed. My guess is there is no antifracture membrane spanning any of the pours or something of that nature.

The whole question is if the areas that are crumbling is patchable. The reason I mentioned pictures is simply to know what the floor is to start with, and whether there is any way to address it in a semi permanent way or if there is a deeper issue with the slab that will continue to cause problems. My guess is that the slab, be it concrete or gypcrete is failing.
 
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Old 10-11-10, 03:33 PM
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We do it on our jobs, though it is sealed prior to install.
Do you install directly to the sealed gypcrete, or do you use an isolation membrane first? Have you installed over only new gypcrete floors? Have you installed over old cracked and crumpled ones, and if so how did you patch/stabilize the gypcrete?
 
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Old 10-11-10, 04:22 PM
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Originally Posted by Shotty View Post
Kolias,

Movement in the subfloor is the #1 cause of installation failure, regardless of coverage of adhesive/thinset, etc. I'm curious when you say all your tile jobs, how many are you referring to. I'd also be curious to know exactally what typr of plywood you're setting on, and what type of glue you are using, these are all important ingredients in the mix.
Your points are well taken Shotty and I only state my experience. It seems that you know very well your trade and I thank you for your input.

I only do residential renovations and the floors I worked on obviously there is no way to know the plywood type since its an existing installation but on my 25 years old place I built it myself and I used 3/4" exterior type plywood (construction grade).

I always use thinset of various brands, the ones that come in a bag and you only add water. Also on the floor jobs I always use a waterproofing additive.
 
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Old 10-11-10, 05:06 PM
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I only do residential renovations and the floors I worked on obviously there is no way to know the plywood type since its an existing installation but on my 25 years old place I built it myself and I used 3/4" exterior type plywood (construction grade).
You need 2 layers of plywood, the subfloor and an underlayment. Plywood underlayment needs to be exterior glue plywood, cc plugged or better.

I always use thinset of various brands, the ones that come in a bag and you only add water. Also on the floor jobs I always use a waterproofing additive.
You should be using a thinset that meets ansi 118.11. It'll say that on the bag. Typically this is dryset mortar with liquid latex additive used instead of water. If you aren't using the right thinset, then you are taking a big chance. Not sure what you are talking about when you say a waterproof additive. Are you saying you seal the plywood first?

Truth be told, while this is an acceptable method, I'm not sure why you would want to use it. There are many other better underlayments for tile installations, cement board, isolation membranes, mudbeds etc. Setting directly to plywood really isnt the way to go. I've seen lots of failures with this method from diy'er's and pros alike. Its risky business if everything is not done right.
 
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Old 10-11-10, 05:35 PM
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Originally Posted by HeresJohnny View Post
Do you install directly to the sealed gypcrete, or do you use an isolation membrane first? Have you installed over only new gypcrete floors? Have you installed over old cracked and crumpled ones, and if so how did you patch/stabilize the gypcrete?

We will typically seal new gypcrete floors, then address anything that needs to be addressed with an antifracture membrane. Typically we use NobleSeal or ECB membrane, and span any cracks or pour/sawcut joints by twice greatest width of the tile ( which is 2 feet for a nominal 12x12). We have installed over old cracked gypcrete, and it's a serious pain. In one case we primed the existing with NacTac primer, and floated a mud bed over with metal lathe inserted halfway through the float in order to make a floating floor. In the other we poured Ardex K15 into the old gypcrete after priming it with P51 and ran ECB membrane over the whole floor to be tiled.

To my knowledge both of these repairs have held up for over 5 years, but I wouldn't expect that they will hold up long term, if for no other reason than the gypcrete continuing to fail as time goes by.
 
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Old 10-11-10, 06:14 PM
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Originally Posted by HeresJohnny View Post
You need 2 layers of plywood, the subfloor and an underlayment. Plywood underlayment needs to be exterior glue plywood, cc plugged or better.

You should be using a thinset that meets ansi 118.11. It'll say that on the bag. Typically this is dryset mortar with liquid latex additive used instead of water. If you aren't using the right thinset, then you are taking a big chance. Not sure what you are talking about when you say a waterproof additive. Are you saying you seal the plywood first?

Truth be told, while this is an acceptable method, I'm not sure why you would want to use it. There are many other better underlayments for tile installations, cement board, isolation membranes, mudbeds etc. Setting directly to plywood really isnt the way to go. I've seen lots of failures with this method from diy'er's and pros alike. Its risky business if everything is not done right.
I use plywood underlayment as you described only where needed. For example when I remove vinyl flooring and half of the old glue stays on the existing plywood floor then I use what you say.

In my present kitchen floor when I did it about 12 years ago the vinyl came off clean and the existing plywood floor was like new. I lay my 10x 10 tiles right on it and up to now the floor is excellent.

The thinset I use is a dryset polymer modified one step mortar in 22.7 kg bags. The instructions say you can use either water or for added strength to use liquid latex additive

I agree with the variety of underlayments available but even if you use them and you dont follow good procedures the job will fail.
 
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Old 10-13-10, 10:03 AM
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A article about tile over plywood.

One of several I found on the internet. A couple of things I found interesting, the writer's comment about success depending on doing it correctly and the other his comment about the number of failures.
 
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Old 10-13-10, 12:55 PM
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Wayne

The person that wrote that article is probably the most knowledgable guy in the tile industry. While the article is 6 years old, it's still accurate today. He ran the CTEF for years. Not sure if he is still affiliated with them. I'm not qualified to disagree with or dispute anything he says.

The key would be to follow each and every step in in the TCNA handbook for installing over plywood. If you do that, you should be ok. My experience however is that most don't know how to install over plywood, don't research it, and don't do it right. Some of the posts in this thread will prove my point on this.
 
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Old 10-13-10, 01:20 PM
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Originally Posted by Wayne Mitchell View Post
A article about tile over plywood.

One of several I found on the internet. A couple of things I found interesting, the writer's comment about success depending on doing it correctly and the other his comment about the number of failures.
Good article Wayne, thanks for sharing
 
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Old 10-13-10, 01:31 PM
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Originally Posted by HeresJohnny View Post
Wayne

The person that wrote that article is probably the most knowledgable guy in the tile industry. While the article is 6 years old, it's still accurate today. He ran the CTEF for years. Not sure if he is still affiliated with them. I'm not qualified to disagree with or dispute anything he says.

The key would be to follow each and every step in in the TCNA handbook for installing over plywood. If you do that, you should be ok. My experience however is that most don't know how to install over plywood, don't research it, and don't do it right. Some of the posts in this thread will prove my point on this.
I didn't have a clue about who the guy was, but what he said made sense to me. I still believe that tile over CBU is the best method but one of the points I was trying to make was that it isn't necessarily the only way to go. I was actually a bit surprised at the very, very low failure rate that he reported.
 
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Old 10-13-10, 03:33 PM
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I was actually a bit surprised at the very, very low failure rate that he reported.
Wayne

The thing to keep in mind here is that the failure rate discussed in the article is for plywood underlayments where all the proper methods and procedures were used. When that is the case, the probability of failure drops dramatically.
 
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Old 11-05-10, 11:24 AM
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response to Here's Johnny from 10-13-10

I've actually had a chance to do the demolition on the bathroom and taken out the vanity and sink, the toilet is still in place. The section of flooring underneath the vanity has no tile under it. The flooring is (and I'm making the guess) that its the 'gypcrete'. The tile was installed directly on top of it. I'm confused by this. The tile job seems to be standing up to the years fine but I'm left with a section of flooring that has no tile and when I stepped on the section, I could feel the gypcrete give a little. A crack appeared (in the gypcrete) about 2 inches from the tile. I didn't want to replace the tile but if I want to install a vanity with an 'open' bottom, there has to be a floor covering the entire area. What would be the correct way to go about an installation? I'm picturing having to put in plywood then cement board, then the tile. But that would throw the height of the floor off for the toilet. And if I do get a contractor for the job, how do I delicately suggest that I prefer a cement board rather than just plywood?
 
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