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-   -   How do you Lay Large Tiles over Plywood Subfloor? (http://www.diychatroom.com/f5/how-do-you-lay-large-tiles-over-plywood-subfloor-11181/)

1655graff 09-01-2007 04:59 PM

How do you Lay Large Tiles over Plywood Subfloor?
 
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:

Jeekinz 09-01-2007 06:06 PM

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?

troubleseeker 09-01-2007 07:29 PM

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.

1655graff 09-01-2007 11:32 PM

Quote:

Originally Posted by troubleseeker (Post 60845)
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?

Quote:

Originally Posted by troubleseeker (Post 60845)
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.

ChrWright 09-02-2007 10:47 AM

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

slakker 09-02-2007 11:59 AM

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...

1655graff 09-02-2007 01:13 PM

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?

slakker 09-02-2007 07:20 PM

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...

troubleseeker 09-02-2007 09:35 PM

Quote:

Originally Posted by 1655graff (Post 60879)
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?




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.

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.

JazMan 09-03-2007 09:48 PM

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

jproffer 09-03-2007 10:20 PM

Quote:

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).

1655graff 09-27-2007 08:48 PM

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?

jproffer 09-27-2007 10:57 PM

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:

Quote:

- 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.

Quote:

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.

Quote:

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.

Quote:

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
Quote:

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.

slakker 09-28-2007 01:30 AM

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:

NateHanson 09-28-2007 07:45 AM

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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