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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (5)03-25-2009, 04:43 AM#1

tilemanct

Tile & Stone

Join Date: Sep 2002

Location: Northeast/Connecticut

Posts: 2,607

How Do You Address The L/720 Deflection For Stone

How do you address the problem of the L/720 rule of deflection on new stone installs? I am running into builders and homeowners who pick out natural stone for floors and when I walk in to quote the install, I have to give them some news they dont want to hear. The second layer of plywood requirement really throws them. I show them the MIA,TCA & Dittra specs. Forget about a mud job! (the best choice) What my competition is doing is telling the customer that the new Dittra XL allows stone over single layer plywood. Thats what it's for. I have lost every stone job because of this lately. How do you handle this?

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (8)03-25-2009, 05:34 AM#2

Stealthfox

Flooring Contractor

Join Date: Nov 2007

Location: St. Louis Mo USA

Posts: 131

just use Ditra XL, like the other guys How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (9)

Also, you might not be considering the fact that virtually all new construction uses engineered I - Beams instead of traditional solid Joists...the deflection numbers for those new beams are much better, and the deflecto calculator on this site for example is worthless for that applications, i realize the new beams dont address deflection between the joists, only parallel to them, but...I personally don't warranty my installs for life anyways (not that I'm necessarily worried they are going to fail) but for new builds in particular, when it comes time for floors, the money is dwindling in relation to the original budget, and I am fully comfortable installing stone over regular ditra, on 3/4 subfloor over I - joists...then again, I usually do MB's and small kitchens, not the 1000's of sq ft that some guys do

Maybe I'm not fully "by the book" and don't y'all hate on me, but a guy's gotta make a living, and I'm certainly a far better option than the other hacks who are gonna walk in with a load of CBU, and still won't address the subfloor issues anyway...Ditra can make even the worst scenario just a little better

believe me, If I could get the homeowner/builder to lay that second layer of subfloor I would...thats the way I'd do it in my own house no doubt

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (10)
How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (12)03-25-2009, 05:35 AM#3

sgrandjean

Healthcare Consultant and Boxer Rescue Volunteer


Join Date: Sep 2004

Location: Bryan, TX

Posts: 964

Get thee to a Schluter seminar!

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (16)03-25-2009, 05:44 AM#4

gueuzeman

Registered User

Join Date: Apr 2008

Location: Albany, NY

Posts: 8,612

Sharpen your chisel, get ready to do repairs. See thread "repair work in 2-5 years."

Perhaps as part of your explanation of the specs, be very specific that Ditra XL is NOT for this application and say that there are others out there trying to sell it as such. Then when the next guy comes in and tries this it's called into question.

Pre-emptive strike.

gueuze

EDIT- I've walked on jobs without s second layer for marble, and been called back by people who thought later the height transition was easier to live with than broken stone. Also seen Carrera fail after 6 months on CBU, tiles broken every 3 ft and 5 ft, almost funny.

Last edited by gueuzeman; 03-25-2009 at 05:49 AM.

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (19)03-25-2009, 05:51 AM#5

Rob Z

Guest

Posts: n/a

Hi Dave,

Your situation is reason #459 on my list How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (20) of why I don't do work for builders or GC's (with very, very rare exceptions).

I find it is a rare occurrence when the homeowner won't go for the extra work needed to ensure a solid installation...it is their house, after all.

How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (22)03-25-2009, 06:15 AM#6

John Bridge

Mudmeister

Join Date: Mar 2001

Location: Rosanky, Texas

Posts: 69,141

There is a Ditra-XL thread in here somewhere, and in it I've stated (from a non-employee standpoint) Schluter's postition on using Ditra-XL for stone tiles over single-layer wood subfloors. I'll try to re-cap here without going overboard.

First off, the TCA no longer requires anything from joists except that the floor be framed to code. We, at the JB Forums, retain the deflecto because it's a good all around test of conventional floor framing. It does not address deflection between the joists, which happens to be one of the major causes of tile floor failure. That's it.

When testing Ditra-XL it was discovered that it SEEMS to work well over single-layer wood floors when stone tiles are used. I say "seems," because the only actual testing so far has been done on a Robinson floor tester. There hasn't been a lot of recorded data from the field.

Schluter would like to specify Ditra-XL for stone floors over single-layer wood, but it does NOT so specify because we have no control over the type and quality of stone that might be used.

I'll leave it at that. You're on your own, amigos. How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (24)

How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (26)
How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (28)03-25-2009, 07:52 AM#7

cx

Moderator emeritus


Join Date: Jul 2001

Location: Boerne, Texas

Posts: 99,123

Let me add to JB's post there that the TCA specs are applicable to ceramic tile only. If a wood floor structure meets code, it's meeting only L/360 deflection minimums. Ain't no code for the L/720 deflection required by the MIA for natural stone and it's rare to find a joist structure that meets it unless that was specified to accommodate a natural stone installation.

Quote:

Originally Posted by Rick

and I am fully comfortable installing stone over regular ditra, on 3/4 subfloor over I - joists..

The type of joist has little or nothing to do with the applicability of the tiling substrate, Rick. In some cases, where the top chord is wider than 1 1/2", you do get some help in reducing the between-joist span, but you'll frequently also have 19.2" joist spacing instead of 16". Having engineered joists is no guarantee you have any better design deflection that you might have gotten with dimension lumber. You gotta have the specs to determine what was designed in there.

Still, as John pointed out, it's the between-joist deflection that's most likely to bite ya. And more and more frequently you're seeing 5/8ths OSB used for subflooring as a "cost saving" measure. No way I'd even set ceramic tile over that, Ditra or no Ditra.

My opinion; worth price charged.

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (32)03-25-2009, 09:59 AM#8

cajtar

Registered User

Join Date: Dec 2008

Location: SoCal

Posts: 146

I just built some overhead storage space in my garage so recently went through all the calcs for stresses, deflection, costs etc of subfloors. What I learned was I-joists are about 50% more expensive per foot than traditional dimensional lumber. So why do builders use it (and I didn't)?
1/ the joists are way stronger and thus can have larger OC dimensions and meet the same deflection spec. i.e. they can reduce their costs!
2/ also b/c I-joists have higher strengh, they can handle longer spans without intermediate headers, posts etc - again a cost saving feature and one that helps to create nicer wide open floorplans.
3/ they are more dimensionally consistent over life than cut wood which means better overall flatness of the subfloor and less squeaks when glue-nailed or glue-screwed per APA requirements.

The wider spacing has a side-effect that has already been noted: deflection between joists. APA requirements seem to not address btwn joist deflection as much as they address shear, thus I-joists appear to have made tile installation MORE challenging, not less. APA form TT-036A shows an example of how the overall stiffness of the glue-nailed subfloor is used to calculated spans to meet L/360. In other words, the glue-nailed subfloor is now considered a structural component necessary to reach the deflection spec!

I agree there are not a lot of houses built that exceed L/360, which I believe are the minimum requirements in the IRC. Newer houses seem to be slowly incorporating L/480, but I'm not aware of any house built to L/720 unless specifically requested to do so - i.e. a custom built house.

Why didn't I use I-joists? sawn lumber was cheaper and as I'm not going to install tile in my garage attic, I could care less about meeting L/720 specs (in fact I designed to L/240 just like a regular attic...)

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (35)03-25-2009, 11:49 AM#9

John Bridge

Mudmeister

Join Date: Mar 2001

Location: Rosanky, Texas

Posts: 69,141

One thing I'd like to add. The Schluter test panels (Robinson floor tester) were composed of a single layer of 3/4 in. plywood over joists centered at 24 inches. As CX pointed out, many if not most floors in production housing have a single layer of 5/8 ply or OSB over two-foot centers. I don't install anything over a floor like that with or without an uncoupling layer, even though certain manufacturers say it's okay. How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (37)

How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (39)
How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (41)03-25-2009, 04:12 PM#10

tilemanct

Tile & Stone

Join Date: Sep 2002

Location: Northeast/Connecticut

Posts: 2,607

Talked with my Schluter Rep today and he gave me schluters take. They will NOT back up any stone job with Dittra XL over single layer plywood. Period! You are on your own. I did get a call back from one bid I thought I lost due to this. They actually called Schluter and got the same answer I gave them on the second layer plwood issue. Let's see where it goes.

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CTEF Certified Installer
I lost my hero on 5-21-16 You will be missed. Semper Fi

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (44)03-25-2009, 04:45 PM#11

John Bridge

Mudmeister

Join Date: Mar 2001

Location: Rosanky, Texas

Posts: 69,141

Dave, please go back and read the replies to the thread. CX and I did a lot of typing to tell you what you've just told me and the others. How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (46)

How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (48)
How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (50)03-26-2009, 05:42 AM#12

tilemanct

Tile & Stone

Join Date: Sep 2002

Location: Northeast/Connecticut

Posts: 2,607

John
Just wanted to make sure you and CX have your "Mavis Bacon" skills up to date. What I wanted to point out was the customer called Schluter and they(Schluter) were very helpful. Schluter not only educates us, they help the consumer. If the consumer feels good about Schluter, and I just happen to speak that language, it's a win win for all. Very few companies do that today.

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Dave

CTEF Certified Installer
I lost my hero on 5-21-16 You will be missed. Semper Fi

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (53)03-26-2009, 06:44 AM#13

John Bridge

Mudmeister

Join Date: Mar 2001

Location: Rosanky, Texas

Posts: 69,141

Oh How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (55)

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (59)03-26-2009, 06:48 PM#14

nj jake

Registered User

Join Date: Dec 2008

Posts: 22

My company sets about 90% marble.We have never had any problems with deflection.Here is how we set,the builders we work for use I joist on 16",3\4 advantech.We follow by tar papering,wiring and mud.The floors we set are anywhere from 700' to 1200'.We do roll hydroflex 80% of the time,and backbutter and set with 3n1 from tec.The houses are high end with lots of granite tops and these people love to have huge parties,so there is lots of weight in these pads.The double plywood is so hard for the builder to deal with.We run into height issues because the builder only wants a mud job no matter what.Which is a good thing.In his defense the home owner and designers pick tile selection to late .

Last edited by nj jake; 03-26-2009 at 06:55 PM.

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How Do You Address The L/720 Deflection For Stone - Ceramic Tile Advice Forums (62)03-26-2009, 07:09 PM#15

tilelayer

South East PA Tile Contractor


Join Date: Aug 2004

Location: Delaware County, PA

Posts: 6,584

im in pa, we do like jake stated and mud all are stone same way, sometimes builder space the joists 12" on center though.

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