New tile install

[sparkey]

Hello everyone! Sorry if this is a repeat but I have benn looking through the history and I am still confused!! I am building my own house and it is almost time to start tiling 12"x12" (this saturday). I am starting in the kitchen with 3/4" Advantech osb over 2x10 joists 12" oc with 13' span so I think I am within L/360? the tile area is going to butt against 3/4" oak. I think I will need to install 1/2" durock (although I kind of like Denshield. Shhhhh) to meet the min 1 1/8"? I am really confused about modified / unmodified thinset under CBU's? How clean does the sub floor have to be for the thinset to adhere to the osb? Okay enough for the first post. thanks for your time.

Dan (since John likes first names it appears)

[bbcamp]

Hi, Dan! Welcome to the Forum.


I'm the engineer, so I'll talk you through the structure. Your joists are good for a ceramic tile installation, but not strong enough for natural stone. Your subfloor is also fine for ceramic tile (again, not for stone). For the 3/4" OSB, the minimum backerboard is 1/4", so your plans to use 1/2" is OK. Dens-shield is rated for floors. We don't like it in "wet areas" such as shower stalls and tub surrounds, and probably not for children's bathroom floors. We say that the thinset under the CBU is for filling in minor variations in the plywood to fully support the CBU, so it doesn't matter what kind you use. Latex modified thinset is stickier, so it is harder to spread, and it bonds the CBU to the floor, something that is not necessary. Install the backerboard of choice per the manufacturer's specs. Pay attention to the nailing/screwing instructions and the spacing between adjoining sheets. Don't forget to tape the joists before, or while you tile.

Butting the tile to wood is OK (leave a grout line), just finish (stain varnish, etc) the wood first so the grout won't discolor it, then mask it off with tape so you don't scratch it, then use a sanded, color matched caulk in the grout line next to the wood, so that expansion/contraction is accounted for.


Phew! Did I miss anything? If so, or you have anyother questions, come back to this thread so we can keep up with your project. Good Luck and Have Fun!

Bob

[sparkey]

Hi bob!
thanks for the quick reply! I am also thinking of putting some marble by the front door just a 2'x7' area. That has 2"x10" on 16" centers but obviously supported right at the rim area is this going to be okay for for L/360 (I hope that is the right term) thanks!

[bbcamp]

For stone, we need to meet the L/720 criteria, and your floor won't without some help. We would have to double the joists in the foyer area to meet the criteria, then we would have to add another layer of 1/2" exterior grade plywood to make the subfloor strong enough. Then, to minimize height, we would install a decoupling membrane called Ditra, from Schluter, co..


About the Marble. Is the front door used for everyday traffic, or for guests only? I ask because marble will scratch and wear a little faster than most materials, so it's usually reserved for walls, and light traffic floors. And some marbles are softer than others, so becareful what you choose.

[e3]

IF THE FLOOR MEETS L/720 WHY THE SCHLUTER ?

[Garrett]

Dan, I would use 1/4" CBU because you will come out very close to the height of your hardwood floor that way. There is no real difference between 1/4" and 1/2" CBU for floor installations.

[tileguytodd]

Bill, Nice Job on this one.Marble is definitly not for high traffic floor areas unless you plan on alot of maintenance.If you dont mind the maintenance and you are willing to beef up the joists,Personnally i would do a true Mudset for the marble.
The ditra is an option certainly and a much better choice than CBU in this instance.A soft marble with quartz veining cannot handle any movement.Absolutly none.(the reason i would choose a mudset) The uncoupling membrane is based in part on the principals of the mudbed,To uncouple the floor from the subfloor.CBU does not truly uncouple the floor from the subfloor at least not nearly as well as Mud or Ditra.
It sounds as if alot of extra work will be involved for a very small area.If you are dead set on Marble.We can talk you through the Mudwork and building up of the Joists etc.

[bbcamp]

Yeah, what Todd said. Actually, I was thinking about the extra plywood and thought the Ditra would keep the overall height down. But that veining thing, too.

[bbcamp]

Remember, when we are talkinig about L/360 or L/720, we're talking about two areas at the same time. The joists and the subfloor. For this marble installation, the joists were checked using our new Deflect-o-lator and determined them to be somewhat lacking. The plywood thickness comes from underlayment supplier recommendations for their product. Schluter specifies "double wood" for stone if you want to use Ditra. I believe the backer board folks do too.

Joist deflection by calculation.

Subfloor by test.

[sparkey]

thanks for the feedback so far!
Okay, time to rethink the marble idea. Back to the CBU's can I go with 1/4" vs. 1/2" and any more feedback on the denshield vs. durock vs. plywood. I have been in trades for about 6 years and could probobly count on one hand the tile jobs I have seen with CBU's used vs. plywood. This application is going to be a kitchen so there is not going to be much water compared to a bathroom. sorry so many questions I just want to do the best thing with the least amount of work Thanks

[sparkey]

Bob: Regarding the 2x7 area with this area being 2' away from the rim joist doesn' t that reduce the amount of deflection vs being in the middle of the span? or am I not understanding the principle? The 3/4" osb is made by huber and is different from 99% of standard osb. here is the info regarding spans maybe this will change things? http://www.huberwood.com/emplibrary/...g2002_Blue.pdf . I don't know if you have time to look this over but I have no idea what I am looking at

[bbcamp]

There is no CBU vs. plywood. Pick an underlayment that you are happy with, and there is a TCA spec. for installing tile over it. We preach CBU as an underlayment, but if you look over in the Pro's Hangout, you can see a lively discussion of plywood.


Dens-shield vs. wonderboard vs. hardibacker vs. etc, Each has its advantages and should be installed per the manufacturer's instructions. We will not endorse Dens-shield in a wet environment, no matter what the manufacturer says.

Keep reading, go to the stores (not for advice, but to check prices), and keep asking questions. That's what we're here for.



And John, in case you're wondering, the "we" is me and my pet mouse!

[bbcamp]

Sparky, thanks for locating that info. However, to my understanding of the problem, and the way I approach the subfloor (plywood or OSB) is to not worry about the degree by which the material exceeds the strength of the minimum specified grade of plywood. Rather, I rely on the testing the CBU manufacturers have done. They use a Robinson floor testing machine which is a 3-wheeled trolly that spins in the middle of a 4'x4' square test sample. The test sample is a plywood sheet with 2x2s nailed to it every 16 inches. The sample is placed on the concrete base of the machine, and the CBU, thinset, tile system to be tested is installed on the top per the manufacturer's specification. The wheels of the machine are individually loaded up to 300 lbs while the machine is spinning. At the end of the test, if the tile or grout are damaged, then the system fails. They test the entire system, except the joists are not considereed at all.

The point to this is that the plywood is part of the system. Deflection is not the overiding criteria. Whatever underlayment you choose, you follow the manufacturer's instructions. Period.

With the joists, that's another topic. There, you can calculate a deflection and relate it to L/360 or L/720.

[John Bridge]

Eric,

Why NOT the Ditra? I think you got your caps lock stuck again