# How do you Lay Large Tiles over Plywood Subfloor?



## 1655graff (Jul 27, 2007)

Can anyone here help us? We're getting 2 conflicting stories and are not sure which is correct. 

We have a plywood subfloor on top of wood joists & rails/planks over a crawlspace. We've talked to 2 different contractors about putting large format (32 inch square) tiles on top of it. We've also read the Tile Doctor Website. 

One contractor is adamant about using "wonderboard" the other is just as adamant bout "floating" the tiles. Both say that large format tiles need _____ (fill in with wonderboard or floating, respectively) because of the way the weight will be distributed. The Tile Doctor does not seem to help us decide since both methods are acceptable for "tiles" (no size specified) in a residential use case.

Which method is best / correct for such large tiles?

TIA!!!!:thumbsup:


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## Jeekinz (Jan 29, 2007)

Seems to me, sq. ft. is sq. ft.

No matter what tile you lay, it would be practicly the same weight.

Four 4x4 tiles should weigh pretty much the same as a 8x8 tile.....right?


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## troubleseeker (Sep 25, 2006)

I'm not clear on your description of "floating" the tiles. Perhaps the tile man said that he had to "float" the floor, a term meaning troweling or pouring a compound to get the surface as close to perfectly flat as possible. The flatness of the floor becomes more crucial with bigger size tiles, and is mucho, mucho important with monsters like you are using. I think both contractors are going the same place, just prefer different methods. Unless the existing floor is already extremely flat, the guy with the wonderboard will still have to "float" any low areas in to level them.


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## 1655graff (Jul 27, 2007)

troubleseeker said:


> I think both contractors...just prefer different methods.


Is wonderboard faster? ...and/or cheaper? What is the advantage of the wonderboard method? 

Likewise, what is the advantage of the other contractor's preference?



troubleseeker said:


> I'm not clear on your description of "floating" the tiles. Perhaps the tile man said that he had to "float" the floor, a term meaning troweling or pouring a compound to get the surface as close to perfectly flat as possible.


 
Let me see if I can explain it. The 1 contractor said he'd imbed some "chicken wire" in a bed of mortar on top of the existing plywood subfloor. The other contractor never said anything about "float" or "floating" or "mortar." He did say he'd use grout over the "wonderboard." That's it.

Also, Is one method more rigid or better on a wood subfloor over a crawlspace?

The 1 contractor that insisted on floating (and also said that he did not like using wonderboard) said his method will stay even over a long time, but wonderboard can lift (e.g., along a corner or edge when its screws pull up), and the edge of very large tiles need to take more abuse since they'll experience more than a cluster of small tiles with the weigt across them all.


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## ChrWright (Aug 19, 2007)

Larger format tiles require much flatter surfaces in order to prevent lippage problems at installation. They are also much less tolerant of deflection in the floor.

It's hard to say who is right without further info. The "float" you refer to is a mortar bed floor. Both make good substrates but the mortar floor will most likely be more expensive as it requries more labor. However, at the hands of a good tile setter, it will yield the best substrate possible for certain conditions. It is also the only way to provide a sloped floor (for a floor drain, for instance).

If the floor is EXTREMELY level & flat, then I might consider wonderboard, durock, denshield--i.e. a sheet good tile underlayment. Another consideration is what transitions you will end up with going to other rooms. Sheet goods are much thinner than mortar beds, for the most part, and can lessen the need for transition strips/angled thresholds. 

Here is an article you may find helpful:
http://www.tileletter.com/Apr06/mortarBed.htm


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## slakker (May 29, 2007)

Or could contractor number 2 mean "float" as installing a "uncoupling layer" with a product like Schluter Ditra... I've used this product for 18x18 tiles and found it worked quite well...


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## 1655graff (Jul 27, 2007)

*I want to thank everyone contributing so far. You are great teachers!:thumbup: *

*ChrWright* => Thanks for the article. So it seems to me that "thin-set" is over wonderboard. Correct? Based on that presumption, it seems it could be well-suited for our floor.

*slakker *=> I'll have to check with him. I presume Schluter Ditra is a ""performance mortars?

So I guess I need to check with both of them on what motar they plan to use. Where can we find more info on or a list of so called "performance mortars"? 

Both of them said they can't do checks on the level-ness or flat-ness of the floor since it still has carpet or linoleum covering. So should we expect a "cost adjustment" (read that upwards) after the demo?

In going back over my notes, I saw that 1 contractor is recommending 1/4 inch wonderboard, the other is saying no less than 3/8 inch IF we go with it. Why would one think 1/4 inch is too thin? ...But the other recommend it?

Are there other questions we should be asking these contractors?


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## slakker (May 29, 2007)

Schluter Ditra is a brand and product name for an membrane that is installed under the tile using thin-set. It acts as a waterproof and anti-fracture membrane. Check out the Schluter web site, it's really cool stuff...


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## troubleseeker (Sep 25, 2006)

1655graff said:


> Is wonderboard faster? ...and/or cheaper? What is the advantage of the wonderboard method?
> 
> Likewise, what is the advantage of the other contractor's preference?
> 
> ...


Using "wonderboard" or any brand of cement backer board is less expensive because it is much less labor intensive than laying a true mud bed, as it seems the other contractir is talking about. However, if the floor is really wavy and out of level (as your case seems) , the mud bed will do a much better job of leveling out the sub floor IMO. All the backer board products will conform to whatever contours are in the existing sub floor, they will not in themselves "level" the floor. Their purpose is to act as a "bond breaker", to isolate the tile from the movement of the wood sub floor, and to provide a compatable surface for the thinset to bond to. I'm not sure of the theory about the edges of the cement backer lifting at the edges as related to large tiles, but sounds like he may have some real life bad experience that he is basing this on. It does seem like he has a much better handle on the importance of an very flat surface when dealing with these very large tiles than the guy who thinks he is just going to nail down some backer board and start laying tile.


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## JazMan (Feb 17, 2007)

Graff,

Before you go any further you need to be sure your subfloor system is sturdi enough for tiles in the first place. Those monsters you're thinking of installing will not like it if there's any give. Let us know the size, spacing and unsupported span of the joists. It would also be nice to know their species and confirmation that they are in perfect condition. What type of house, how old, where located etc.

We then need to know of what the subfloor is made of, in detail. If these factor don't pass, then nothing will work right.

As far as your selection goes..........YIKES! Did my eyes see they are 32" in size? Are you sure you want tiles that are that large? Your floor had better be as flat as your kitchen table and as stiff as your concrete driveway. Even then you're going to have some lippage, no way to get around that. 

If it were me....I would reconsider the tile size issue. More on the installation method once you answer the questions I asked.

Jaz


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## jproffer (Mar 12, 2005)

> In going back over my notes, I saw that 1 contractor is recommending 1/4 inch wonderboard, the other is saying no less than 3/8 inch IF we go with it.


Tell Contractor #2 he's full of #2. The backerboard has nothing to do with making the floor more rigid. The floor should be strong enough for the tile you want to use before adding the wonderboard. The ONLY purpose for any product between the plywood and the tile is to decouple the tile from the plywood subfloor. Tile and wood expand and contract at different rates...if you bond the tile (especially 32" tile...may I just say...dayyyyummmmmmm) directly to the plywood, as the plywood takes on moisture and expands (for the sake of argument and clarity, lets exagerate and say it will expand....**shrug**...a full 1/2"..and the tile, to keep the same exageration, would expand say...1/4". The plywood would pull the tile apart and form cracks).


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## 1655graff (Jul 27, 2007)

*Thanks and...*

FIRST and foremost, I want to thank you all for your help so far. Please read this update and let me know what you think. Thank again and in advance! :thumbsup: 

Based on your^all's posts, we decided to get more bids:
a) from Schluter DITRA contractors, and
b) from friends' contractors.

The results (for our 400 sqft):
- 2 recommend wonderboard or another backerboard. 1 original ('A'); 1 new contractor ('B'). A's bid ($6.3K plus) and B's ($4.5K plus) backerboard. Both include demo.
- 1 recommends "mud and float" (over 30# membrane & chicken wire). He's the other original contractor. Bid: $8.5K plus grout; and includes demo. He's called me and says he's willing to negotiate "some." He calims that he knows of DITRA (not tried it yet) and also uses DenShield, but his developer clients prefer his bid recommended method.
- 1 recommends DITRA. He says it would be "best" be over T&G replacing exisitng plywood subfloor (since kitchen is 40% of the floorspace). He crwaled under the floor to look at the joists, and was going to check the joists against deflection calculator, but we didn't hear back from him on these results. He wants T&M (time & material) or we give him a flat rate figure we want it done for that he will accept or reject.
- 1 recommends an unknown membrane (he won't tell us what he uses, but its not DITRA since they only use DITRA outside, or was it over concrete). He guarantees 1/16" seams. His bid: $8.9K. Finally, he eliminates his liability since demo and subfloor prep must be certified by us as "OK" before he'll begin.

I'm not sure which is reasonable. And so now, 1 of the backerboard guys is also wanting to bid on some remodeling work we also have in these rooms. Should we say "yes" but only if he bundles and discounts?


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## jproffer (Mar 12, 2005)

The only comments I could make on any of them, save the last...see below, would be based on my personal preferences.

I prefer to use durock or some other soild backer rather than Ditra. So I would go with that product, no matter who was doing the install. If they weren't agreeable to using what I preferred, then they could shove off and I'd find someone else.

Did anyone except the next to last guy even check the framing? If not, why not? (I'm not asking you to read their minds...but you should ask them). He seems to at least know what he's doing. Measured the framing members and is going to run the numbers on a deflection calculator. That sounds reasonable. I hope you hear back from him eventually.

Now then...the last guy:



> - 1 recommends an unknown membrane (he won't tell us what he uses, but its not DITRA since they only use DITRA outside, or was it over concrete). He guarantees 1/16" seams. His bid: $8.9K. Finally, he eliminates his liability since demo and subfloor prep must be certified by us as "OK" before he'll begin.


That just stinks throughout.



> recommends an unknown membrane (he won't tell us what he uses...


Uhhhh....OK...is he afraid the rest of the world might find out?? If he won't tell you and SHOW you, by brand, what EXACTLY he is using, one almost has to assume it means it's something that's not made for this purpose.



> He guarantees 1/16" seams


Why the he\\ would you want 1/16" seams with 32" format tile? Maybe that's something you decided yourself, and if so, I'm sorry for what I'm about to say...I think that's going to look silly. Lay out several tiles dry, butted up tight (because that's pretty much what you're going to have) and make sure you like the way it looks.



> Finally, he eliminates his liability since demo and subfloor prep must be certified by us as "OK" before he'll begin.


Tell him if you knew what was adequate and what wasn't, you wouldn't be paying him


> His bid: $8.9K


 to do the job. As the professional, and I use that term very loosely, it's HIS job to determine what needs to be done to do the job correctly...not yours. BTW, without looking underneath at the framing, there's no way he can claim to know how to do the job correctly...expect a change order for additional support if the framing isn't up to snuff.


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## slakker (May 29, 2007)

It was hard to follow your thread between 1, 2 and a, b... so I may be a bit confused as to who said what...  but either way, my spidey-sense tells me to be careful with both of them...

Maybe check out the more reputable tile distributors to see who they would recommend as tile setters...

But with only 400 sq ft, maybe it's a project you can take on yourself? :thumbsup:


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## NateHanson (Apr 15, 2007)

I think the last guy trying to remove himself from liability if it goes wrong really stinks. 

I also think the guy asking for T&M, OR you pick a number and he decides if it's high enough for him is rotten. I'd stay away from both of those guys.


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## 1655graff (Jul 27, 2007)

Evryone, again, thank you. 

We also think the last guy is BS. Thanks for the confirmation. 

I also agree with the point about the DITRA-guy's bidding approach, but since he is the only one to validate the joists & subfloor (or at least appear to be doing so) We've not dropped him yet. 

*I also like the idea on checking with local distrubutors, but who?* It seems HD and Lowes are the suppliers for most of these guys. Who else should we be checking with?

BTW, I'd like to be a bit more clear in my head... 
- One friend hated the job the tile retailer originally contracted for them, but they complained so much that the retailer eventually came through with a new contractor that tore up and replaced the floor. 
- 1) We REALLY don't want that to happen, and 
- 2) What's the difference between a "local distributor" and a retailer (theorhetically and practically speaking)? Is it merely who's their customer?


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## slakker (May 29, 2007)

I live in Vancouver Canada, and in the local area, we have 3 or 4 really good specialty tile distributors. Olympia Tile is one that has US locations... They also have an "advertising wall" in their showroom for tile setters... They have selections that you can't get from HD, and if you're a tile setter or designer, you can get up to 40% discount off the list price of tiles. We found slate for as low as $2.00 CDN/sq ft once.

Where abouts are you? I'm hoping there are some reputable tile distributors where you are... The difference I find is not whether they are retailer or distributor... they some times sell the same product from the same manufacturer... I find it's their business practice... are they only focussed on making quick profit or looking to find the balance of profit and repeat business.

I hate to say, it's a landmine out there... But one thing is for sure.. if the guy shows up with a big bag of those little "cross hair" spacers and starts using them like crazy, tell them to take a hike...


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## jogr (Jul 24, 2007)

It is very common for floor joists and subfloors that were originally installed for a carpet or sheet surface to not meet the TCNA requirements for tile. I wouldn't hire anyone who did not evaluate your floor structure first before giving you a quote. And don't ask them to do so; consider it to be a screening test to determine if they know what they are doing.

If they get past this point, ask them if they follow the requirements in the TCNA handbook. If they say "No" or "What's that?", say goodbye. 

If they say yes, ask them what defelection your floor currently is and how they calculated it. The answer should involve identifying the dimension of the lumber, the species of the lumber and the span of the lumber and then using a reference table or program. Ask them how thick your subfloor currently is. Ask them to show you the pages in the TCNA handbook that state that this deflection and subfloor thickness is ok for the 32" tile you want. 

Ask them to show you the pages in the handbook that detail their method of installment and to put on the contract that they will follow the TCNA requirements for this method. As you are finding out, there are a number of methods that work as long as the correct procedures are followed.

If they are really into doing a good job they will be thrilled to talk about TCNA requirements and show you how they are meeting them. Those are the ones you want to hire and they may very well be more expensive than the "git-r-done" guys that are fast, cheap and hard to get hold of when the tile starts cracking.


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## 1655graff (Jul 27, 2007)

slakker said:


> Where abouts are you? I'm hoping there are some reputable tile distributors where you are...


East Bay of San Francisco Bay Area. ...specifically: San Leandro, CA (the other CA :wink: ) & zip is 94577.


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## 1655graff (Jul 27, 2007)

Seeing the hell-on-earth that "House Amuck" has been going through and taking in your advice given so far in this thread (e.g., yours "jogr" thanks!:thumbsup: ), I am wondering how we can effect /make sure we:
- a) evaluate and hire a good/well-qualified contractor, and 
- b) ensure the kind of working relationship needed to complete a job well done?

*Jogr (and others):* 
- a) Is it "too late" for those contractors/bidders that haven't gone down into the crawl space to look at the joists? 

I ask because I'm thinking I can go back to the 3 we are most interersted in and ask them some questions to help me "understand better." And so use that opportunity to evaluate them more fully.

- b) It seems to me to be easy to put words in a contract around abiding by the handbook, but what all will we need to do to know they aren't skimping? We aren't building inspectors so what homeowner/novice steps should/can we take since we aren't home all day when this work will take place?

- - - - - - - - - 

Finally, to help in the discussion, here's a quote (with formatting added) that seems to sum it up from House Amuck's thread on their bathroom flooring problems:



AtlanticWBConst. said:


> I can't tell you how many times I am so dissapointed when I see really poor substandard work. I really feel for the property owners...Bottom line is that there are some people that do this job simply for the money, and then there are some that want to do the best job possible on any given project and look forward to seeing a very happy customer that has a finished .... high quality job.
> - We are constantly on the look out for better materials and better methods. We want all our work to be done expertly, a notch better than the best.
> - We feel our customers have put their trust in us, and they deserve the best. Our goal is to deliver it .... no matter what.
> - We only hire subcontractors who have the same ethics as we do. There are many contractors out there that feel the same way.


And, here's a link to that thread:


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## jogr (Jul 24, 2007)

It is difficult to "rehabilitate" a contractor to get him to do things right if that is not his standard operating procedure. In order to do that you have to be the expert, watch his every move and insist on doing things your way. That tends to be very frustrating for both parties and if you already had the time and expertise you'd just do it yourself anyway. 

So if you've asked a contractor for a quote on installing 32" tiles (which are going to be very sensitive to subfloor/structural conditions) and he didn't check out the structure before giving a quote then I don't think I'd continue on with that contractor.

I wish I had an easy answer for how to find a good contractor. All you can do is ask as many questions as possible, check out their previous work and reputation and hope for the best. We all want to get a reasonable price and not pay too much but, in the end, don't base your decision on price. Take that out of the equation and base your decision on who you think will do the best job.


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