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Unread 10-02-2015, 11:32 AM   #1
dr_innovation
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6x24" Tile install questions DITRA vs CBB and Orientation with respect to Joists?

Want to install 6x24" Porcelain Floor tiles (9mm thick) in our renovated kitchen. We want to minimize the high differential to the wood floor outside the kitchen, which is 1/4 higher than kitchen linoleum (which I plan to remove).

I am considering DITRA or 1/4" Wonderboard.. Reading suggests DITRA should be a bit thinner.. is it actually thinner in practice?

The floor has 5/8 OSB nailed/glued on I-Beam Joists (11 7/8" high, 2.5" header/footer, 16in OC, 17.5' span. The manufacturer spec says provides L360 at 40 PSF LIVE LOAD, 15 PSF DEAD LOAD for a span of 18'8".)

The with spec of just over the minimum L360 and 15 year old house, am I pushing it too close to the deflection limit? (If it matters, the kitchen is directly centered over the center beam of the house, so actual distance from the support to any point the kitchen is under 8'). Will I need to add web-stiffners to the beams?


Should I orient the 24' dimension of tile across or parallel to the joists? (or does it not make a difference)?
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Unread 10-02-2015, 01:18 PM   #2
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Hello, Terry. Welcome to the forum.

I'll answer your last question first. It makes no difference which way you orient your tile over a proper subfloor and joist system.

As for the rest of your questions: Given the information you've provided on your joists, I'm not concerned about them as much as I am about the 5/8" subfloor. It appears the joists are not overspanned, and if they're not cut up or otherwise damaged, I think they're probably fine. Again, that's just based on what you've provided.

The subfloor, however, is the bare minimum required for a tile installation, and as you alluded to earlier, time and wear can take it's toll on construction materials. Even when it's new and installed properly, I wouldn't install tile over a 5/8" subfloor. I would want 3/4" plywood, or I'd install a minimum of 3/8" plywood over the 5/8". Properly installed, either of those options would make for a good subfloor.

I know that's probably not what you want to hear given your concerns about the height, but our primary concern is that you have a long-lasting floor as opposed to one that is the height you want but doesn't hold up. Of course, it's your floor and your money, you can proceed as you wish.

Ditra is probably as thin of a membrane that you'll find, and it's about 1/2 the thickness of a 1/4" tile backer. The only one thinner that that is Greenskin, which is about the thickness of a dollar bill. I'm not familiar with the specs of that product, though, so I'm not sure if it can be installed directly over a 5/8" subfloor.
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Unread 10-02-2015, 03:06 PM   #3
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Linoleum is usually installed over 1/4" luan plywood, and that needs to come up as well, which will give you a little more height leeway. If they glued that in place, it can be a major mess to get up, and even if they didn't, the numerous fasteners can be a pain.

If the 5/8" is not T&G, it will need some work as well, as the joints MUST be supported along the long side of the panels.
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Unread 10-03-2015, 08:47 AM   #4
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Thanks.. forgot there might be luan.. oh more fun

Kman.. I recognize the 1/8 is the spec hight of DITRA.. but that is before thin set below and above, my question was about installed height. Of course now I realize I'd need this set below the CBU so the added height affects them both.

Jadnashua I had see Schluer T&G requirement. Wast not sure how to check for T&G. Dug around in the ceiling below kitchen till I found a visible OSB markings... it says it is Grant Dryguard 23/32 T&G ( not 5/8 I had measured in a hole by an air duct.. maybe they shaved it or a OSB sliver fell off installing the ductwork).

With respect to the added ply.. Schluter manual say 5/8 OSB with 16" OC is sufficient.. and their warranty is 10yeas if following their directions. Read lots of thread here suggesting thicker, and a few here and on other sites saying 5/8 only if floor is in perfect condition. But I've also found very few post about actual problems (except bad installations with improper thin set).


I've read that bigger tiles are more demanding. Is z 6z24 still L360? So with 23/33 (3/4" nominal) it seemswith the I-beams and the space that is just short of L480 on the speces. I'm well over the Schuler minimum rating if things are still in good shape (which they seem to be). So are people just very cautious or is Schluer just overselling their product and hoping few go for the warranty? Is there a dynamic test I can reasonably easily do to determine if its still meeting the deflection requirements (L360).
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Unread 10-03-2015, 05:24 PM   #5
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Schluter's recommendations (and most companies) are for NEW materials. It's hard to say what condition some older stuff may be in. 23/32" is the nominal 3/4" material, and if the OSB has not been subjected to excessive moisture and started to delaminate, it should be okay. Not all OSB panels are created equal, though. If the stuff doesn't look all mangled, you should be okay to tile over it.

The biggest issue with larger tile is the flatness of the floor, not a requirement for a stiffer one. Ceramic is ceramic (and porcelain is a type of ceramic). Now, will it hurt to add more, not from a functionality viewpoint, and on an older install, adding a new layer gives a better margin of error if there's any issue(s) with the original materials.
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Unread 10-11-2015, 04:23 PM   #6
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Welcome, Terry.
Quote:
Originally Posted by Terry
(If it matters, the kitchen is directly centered over the center beam of the house, so actual distance from the support to any point the kitchen is under 8')
It matters not at all, Terry. The distance you need to know is the unsupported span of your joists. Has nothing at all to do with the room size or the location of the area to be tiled, nor with the location of the supports, only the unsupported span(s) matters.
Quote:
Originally Posted by Terry
With respect to the added ply.. Schluter manual say 5/8 OSB with 16" OC is sufficient.. and their warranty is 10yeas if following their directions.
Keep in mind, Terry, that all the test data any manufacturer has for those subflooring products comes from new material, in perfect condition, near-perfectly installed over joists with zero deflection. You'll have none of those conditions, nor will you have near-perfectly installed Ditra or tiles. You need to fit all that information into your own personal risk tolerance level.
Quote:
Originally Posted by Terry
Is z 6z24 still L360?
I'm having a bit of trouble figgering just what you might be axin' there.

My opinion; worth price charged.
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Unread 10-11-2015, 07:00 PM   #7
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DITRA over vinyl, which thin set?

Thanks CX and Jim. CX.. my last question there was if the spec depended on tile size, so if L360 is still the spec for 6x24" tiles.. I could not find any definitive.

I hate to but after we started looking deeper into our kitchen tile install, the sheet inlaid vinyl is over 1/4 plywood which at least under the range is screwed down on joists and maybe stapled between. Unfortunately the all the cabinets installed over both, and we just had the granite counters installed so taking out the cabinets is not going to happen. The vinyl is in very good shape so the wife is now thinking maybe we leave it in place as the Ditra manual says we can install on vinyl. (I've read dozens of thread.. and know the majority will say it should be removed). I'm pretty comfortable with the risk for the structural side. Only remaining question is the Vinyl.

So 3 new questions..
1) if we use DITRA over inlaid sheet vinyl do we use modified thin set (better adhesion to vinyl), but since vinyl is (largely) waterproof is that a problem? I ask since DITRA instructions say only non-modified between DITRA and tile because modified won't dry properly, how will it dry between DITRA and Vinyl ?

2) While DITRA says you don't have to allow the underside bounding thin set to dry before laying the tile. Will that make the drying issue worse, or since the DITRA is a water barrier is it of no consequence?

3) If we do try to remove the vinyl and wood, it is there is a reasonable way to cut around the cabinets with common tools. I've seen some videos using a collection of special saws. But we are doing this all on a budget (and expect to move within a year or so..)
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Unread 10-11-2015, 08:51 PM   #8
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You'll hafta help at least one of us with the term "inlaid sheet vinyl," Terry.

If you'll go to the Schluter Ditra website and download the Installation Handbook, in which you'll find exactly the information you'll need to install your Dirta over an existing vinyl floor in a wood framed structure. Read everything in that little section. It's brief, and clear.

I don't know if your "inlaid sheet vinyl" is or is not cushioned. I don't know if it's perimeter bonded. I don't know if it's the only layer of vinyl under there. I do know that the presence of a 1/4" layer of plywood under the vinyl means it's not installed over a "structurally sound substrate" in the parlance of the ceramic tile industry or Herr Schluter.

That aside, if you wanna install over it anyway, read the part about nailing the existing vinyl floor ever 4 inches in both directions before preparing the surface for Ditra.

1. The drawing and instructions with that installation method (D-V-T-15) clearly calls for a "fast-setting latex portland cement mortar" for the installation of the Ditra. They provide some alternate choices in the Method.

2. Matters not at all. See #1.

3. A toe-kick saw would be the weapon of choice if I planned to properly remove the vinyl and 1/4" (probably Luaaun) plywood layers. See Jim's caution in post #3.

But if you're content to slide a less than well done installation off on the next owner in a year or so, I'd just tile over the vinyl and hope for the best. Don't think I'd be happy with that.

My opinion; worth price charged.
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Unread 10-11-2015, 10:09 PM   #9
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Question

Thanks CX. Inlaid vinyl is a solid vinyl material (which I've found on other sites as being not cushioned).


I did read the manual, .. but the full paragraph says

Other Considerations
DITRA and DITRA-XL are adhered to the vinyl flooring using a fast-setting latex-portland cement mortar suitable for bonding to vinyl. As an alternative, a suitable cement-based embossing leveler or an appropriate latexmodified
thin-set mortar can be used to skim coat the vinyl to provide a bonding surface. When skim coat is cured, DITRA and DITRAXL are adhered to the skim coat using an unmodified thin-set mortar. See page 23 for discussion on latex-modified thin-set mortars
which has a citation to page 23. On that page it says not to use Latex-modified because it won't dry. The inconsistency left me wondering. I guess the alternative make more sense to me, so maybe I'll go that route (or maybe just give up and do laminate).


yes, I knew about the toe kick saws but at $300+ to buy and locally is $20/hr ($80 to rent for 4 hour min), I was trying to avoid that large a cost. And with multiple inside corners that they won't be able to reach then I have to find a way to handle the corners. I've seen some flat-blade saw used but that would not work under the cabinet edge for the corner. Is there any clever way for the corners?
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Unread 10-11-2015, 10:31 PM   #10
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A lot depends on what it is you're trying to cut through. If it's just 1/4" plywood, it's actually pretty flimsy, and I've scored it halfway through and broke it off, then cleaned up the edge with a reciprocating saw.

If it's something thicker, you may have to cut through pretty much all of it with a reciprocating saw. The part you have to be careful of is to not cut through any plywood below.

Also, one of the oscillating tools may come in handy in the tight places.
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Unread 10-12-2015, 12:54 AM   #11
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Quote:
Originally Posted by Terry
On that page it says not to use Latex-modified because it won't dry.
And, again, that's why they call for the use of a rapid-setting mortar for application over the vinyl unless you use one of the alternative methods such as skim coating with a latex modified mortar first and letting that dry to form an acceptable substrate for the unmodified mortar.
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Unread 10-12-2015, 06:25 PM   #12
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Thanks for all the feedback. The direct feed back, as are almost all (but not quite all) threads on this forum, are very against setting over vinyl, so I've been reviewing the overall time/cost/risks. I might have a lead on a lower-cost toe-kick so just fishing for ideas/data before I discuss another route with the wife. One of her other complaints is how long it will take to do, start to finish. Ideally its a weekend + 1 day for grouting (which she can do)). Adding drying time for the thin-coat for DITRA will add a day and using fast-setting latex-portland cement mortar (Which I did not know was s different type) adds cost and maybe more risk. Adding the other costs (mortars, DITRA, nails,etc), maybe removing the 1/4ply and vinyl and adding wonder board might actually be both lower risk and cheaper -- if I can keep the time down..

I've seen threads on pulling up whole floors down to the joists by cutting it. So I wondered, if I cut with toe-kick around the edges, how plausible is it to pull off the 1/4" plywood and vinyl all at once. However I could find no thread on that, then again they are very common terms when searching.
I checked a bit more and the screws seem to only be on the edge, so if I cut with a toe-kick I should not hit the screws. Not sure if plywood is also glued.. any way to tell? The glue on the vinyl is everywhere and will be a bear to remove.. so if I have to take up the vinyl and plywood, is seems it is probably better to take them both up at once, nes't ce pa?
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Unread 10-12-2015, 06:27 PM   #13
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Yes, its common to pull both up at the same time.
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Unread 10-13-2015, 02:08 PM   #14
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Are you sure it is 1/4" plywood under your flooring. In Utah and the bits of Colorado I have worked in it is pretty standard to use 3/8" particle board under. I don't see plywood very often, can't recall every tearing any out.

If they did as crappy a job as most the floors I have torn out the board isn't glued down, it is just stapled with a 1/4" stapler. It comes up pretty easy most times but you have a ton of staples to pull because they just pull through the board. I use my skill saw to grid the floor out and pull it up in 2'x2' sections. I score the floor at the cabinet edges and then just break it off and maybe use a chisel to clean up any of the edges that didn't break clean.

Is your house subfloor really 5/8" osb, it seems 23/32" OSB T&G is really common the last 10-15 years and many mistakenly measure it as 5/8".

What is your wood floor thickness? I just installed tile in my house up to the hard wood and had to use Ditra XL to get the tile to be flush with the 3/4" hardwood.
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Unread 10-13-2015, 08:31 PM   #15
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Bryan:
thanks.. yes I'm sure its plywood,it is thorboard brand plywood (did not find much about that brand). My house was the one built (and inhabited) by the builder that did most of the houses on the street. So maybe had a few more upgrades.


In a later post I did confirm/correct.. the subfloor is 23/32" OSB T&G. Nailed and glued (or at least I believed glued could see a few glue runs down from the OBS when I looked at the beams in the basement). Beams are LPI32-Plus, with 11.75" high with max span of 17'6" (measured to center of beam), which I round up to 18'. Reviewing the spec with the 23/32 OSB it would be L480 at 19'.

The wood floor is 3/8" thick engineered oak glue down onto the same type of 1/4" plywood.
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