Ceramic Tile Advice Forums - John Bridge Ceramic Tile

Welcome to John Bridge / Tile Your World, the friendliest DIY Forum on the Internet


Advertiser Directory
JohnBridge.com Home
Buy John Bridge's Books

Go Back   Ceramic Tile Advice Forums - John Bridge Ceramic Tile > Tile & Stone Forums > Tile Forum/Advice Board

Sponsors


Reply
 
Thread Tools Search this Thread
Old 04-30-2019, 03:54 PM   #16
PC7060
...unrepentant, detail focused, over-analyzer.
 
PC7060's Avatar
 
Join Date: Jan 2013
Location: Virginia
Posts: 2,619
Follow up to Jim's comments on the required second layer of plywood; best to attach the second layer only to the subfloor at the 1/4 and 3/4 points between the joists. If you look in the libery in the blue bar above you see a section on wood subfloor with an article by Woeste and Neilson posted by John Bridge.
PC7060 is offline   Reply With Quote
Old 04-30-2019, 04:14 PM   #17
jadnashua
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

 
Join Date: Jul 2004
Location: Nashua, NH
Posts: 12,873
Nobody will guarantee your install will fail if you don't reinforce things, but nobody will guarantee it won't, either. What the industry has found, though, is that when you meet their minimum requirements, have good workmanship, and follow the instructions on the materials involved, it does last.

Some slate is VERY strong, some is little more than compacted mud. You can get an idea on yours if you take a few different colored ones and submerge them in a large pan of water for 24-hours. A good, dense, real slate will remain hard with no color transfer if you rub it. A cheap 'fake' one, will start to deteriorate and you'll get a lot of staining if you were to rub it with a light colored cloth.

As I said earlier, though, unless the original design parameters called for (the eventual) installation of stone, they rarely spend the extra money to get the floor up to L/720. There are methods you can use to improve your floor's strength. It might call for a second beam beneath to shorten the spans.

Keep in mind that the subflooring manages the deflection BETWEEN the supports, the supports manage deflection ALONG them. Both must be at or above the minimums to support stone tile. At the spacing you have, it's fairly easy to add enough subflooring to accommodate the in between strength required, but that does not appreciably improve the along the support strength.
__________________
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
jadnashua is offline   Reply With Quote
Old 04-30-2019, 05:26 PM   #18
BasicDIY
Registered User
 
Join Date: Apr 2019
Location: Eastern Shore, Maryland
Posts: 11
I think I have a good slate, but then I thought we were doing this right based off of information found on other sites, youtube and the guys at the tile shop...
so my slate is currently soaking in water.
__________________
Catherine
BasicDIY is offline   Reply With Quote
Old 04-30-2019, 06:35 PM   #19
PC7060
...unrepentant, detail focused, over-analyzer.
 
PC7060's Avatar
 
Join Date: Jan 2013
Location: Virginia
Posts: 2,619
Catherine - no issues, we are all happy to help. The folks on this site have been very helpful to me on several projects and we will do our best for you.

SilentFloor deflection formula on pg. 16 of "TJI 15 25 35 55 DF - March 1992.pdf"

TJ Def = 22.5 w L^4/(EI) + 2.67 wL^2/(d*1E5)

Using this formula, I've calculated the deflection of your floor based on the information you've provided:

L = Clear unsupported span = 12.5'
w = uniform load in pounds per lineal foot = 50 * 16/12 = 67 LBF/LF
EI = Lookup TJI 25 DF (table on page 16) = 322 X E6
d = height of joist 11.875

Deflection @ 50LB/SFT =0.137" (L/1094)

Given the unknowns of the grade and conditions, I've reduced the rating of the floor by 25%.

With 25% Risk Factor

Deflection @ 50LB/SFT =0.172 (L/874)

Which result in a estimated rating of ~ L/870 which exceeds the rating requirement of L/720 for natural stone. Nice.

I qualitatively verified the quantitative numbers using the span charts on pg. 5 of the referenced document.

Minimum L/480 LIVE LOAD DEFLECTION

Joist Depth 11.875
Joist Series TJI 25 DF
Spacing: 16" OC
Max rated span to meet L/480: 19'-3"

So this aligns with the calculated number since you've stated the floor span is 12.5' which is 60% shorter than the rated limit.

-------

Just to be conservative, I also calculated the deflection assuming a TJI 15 joist.

The calculated deflection rating for the TJI 15 is:

Deflection @ 50LB/SFT =0.154" (L/972)

With 25% Risk Factor

Deflection @ 50LB/SFT =0.193 (L/778)


So that checks good too.


So what does this mean? Given the information provided along with the manufacturer published performance data, your floor should perform well for natural stone given:

1. Given the poor nailing skills demonstrated by the builder, you should screw down the original sub-floor to the TJI a minimum of every 15" (I'd do 12"). Use 2" GripRite deck screws

2. You install a second layer of plywood over the existing sub-floor; minimum of 1/2", I'd recommend 5/8". Fasten the second layer of plywood to the subfloor with 1 5/8" GripRite deck screws at the 1/4 and 3/4 points between the joists. DO NOT screw it directly to the TJI. The explanation of why/why not can get long and drawn out so I'll leave it the the article I reference earlier.

3. You properly install a decoupling layer such as:
a. 1/4" CBU (or 1/2") with the correct thinset layer between the CBU and plywood floor
b. Schluter DITRA (my choice).

FYI: I provide all the numbers and formulas so the end users can check the math and "own" the solution.

And there are no guarantees implied or stated!

Last edited by PC7060; 05-01-2019 at 06:35 AM. Reason: Corrected screw size
PC7060 is offline   Reply With Quote
Old 05-01-2019, 09:44 AM   #20
BasicDIY
Registered User
 
Join Date: Apr 2019
Location: Eastern Shore, Maryland
Posts: 11
What wonderful news it was a great start to my day. Thank you so much. Where do I send the homemade cookies?



This weekend we are pulling up the CBU, I'll post pics.
__________________
Catherine
BasicDIY is offline   Reply With Quote
Old 05-01-2019, 09:59 AM   #21
PC7060
...unrepentant, detail focused, over-analyzer.
 
PC7060's Avatar
 
Join Date: Jan 2013
Location: Virginia
Posts: 2,619
Quote:
Originally Posted by BasicDIY
What wonderful news it was a great start to my day. Thank you so much. Where do I send the homemade cookies?
Sounds great, but I thought the Eastern shore prized commodity was Blue Crabs!
PC7060 is offline   Reply With Quote
Old 05-03-2019, 12:25 PM   #22
BasicDIY
Registered User
 
Join Date: Apr 2019
Location: Eastern Shore, Maryland
Posts: 11
Researching the ditra, can we use the 1/8"?
__________________
Catherine
BasicDIY is offline   Reply With Quote
Old 05-03-2019, 12:42 PM   #23
PC7060
...unrepentant, detail focused, over-analyzer.
 
PC7060's Avatar
 
Join Date: Jan 2013
Location: Virginia
Posts: 2,619
I thought the standard Ditra is about 1/4” and DitraHeat is 3/8”. Is there a new versions that’s thinner?
PC7060 is offline   Reply With Quote
Old 05-03-2019, 02:34 PM   #24
cx
Da Home Builder
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 87,711
I think the standard Ditra measures right at 1/8th of an inch tall, PC, little higher installed. Ditra XL closer to 3/16th on its own. I dunno about the Ditra Heat, having never used it.

My opinion; worth price charged.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is offline   Reply With Quote
Old 05-03-2019, 02:47 PM   #25
Kman
Moderator
 
Kman's Avatar
 
Join Date: Nov 2006
Location: NW Arkansas, Ozark Mountains
Posts: 10,559
Ditra XL is 5/16", and Ditra heat at 1/4". Ditra is 1/8" installed.
__________________
Kevin

The top ten reasons to procrastinate:

1.
Kman is offline   Reply With Quote
Old 05-03-2019, 03:27 PM   #26
PC7060
...unrepentant, detail focused, over-analyzer.
 
PC7060's Avatar
 
Join Date: Jan 2013
Location: Virginia
Posts: 2,619
Kevin/CX - Thanks for the info!

Quote:
Originally Posted by Catherine
Researching the ditra, can we use the 1/8"?
Yes!
PC7060 is offline   Reply With Quote
Old 05-03-2019, 03:37 PM   #27
cx
Da Home Builder
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 87,711
I just hate it when we gotta go to measuring stuff, but......

I measure Ditra at 0.134 or 0.135 inches. More difficult to mic than is Kerdi. That's less than 1/64th-inch more than 1/8th of an inch or about 9/64ths.

I measure Ditra XL at 0.285 or very close to 9/32nds of an inch. More than 1/4, less than 5/16ths.

Both samples measured came from Schluter in their Handbook. My Handbook is too old to contain any Ditra Heat and I have none in the shop to measure.

If Kevin wants to say his Ditra XL is bigger than mine, I'm not gonna argue.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is offline   Reply With Quote
Old 05-03-2019, 03:47 PM   #28
PC7060
...unrepentant, detail focused, over-analyzer.
 
PC7060's Avatar
 
Join Date: Jan 2013
Location: Virginia
Posts: 2,619
Nice! Love it when we get down to fine details.
PC7060 is offline   Reply With Quote
Old 05-04-2019, 05:02 AM   #29
ss3964spd
Registered User
 
ss3964spd's Avatar
 
Join Date: Jul 2005
Location: Fairfax, Va
Posts: 1,818
Send a message via Yahoo to ss3964spd
Yup, Schluter says Ditra Heat is 1/4", while Ditra Heat Duo is 5/16".
__________________
Dan
---------------------------------------------------------------------------------
If I recall correctly my memory is excellent, but my ability to access it is intermittent.
ss3964spd is offline   Reply With Quote
Old 05-04-2019, 06:39 AM   #30
cx
Da Home Builder
 
cx's Avatar
 
Join Date: Jul 2001
Location: Boerne, Texas
Posts: 87,711
Yeah, but in their current Handbook Schluter thinks Kerdi is 8 mils thick and Kerdi Band is only 4 mils thick, Dan. That's how we got into this measuring business to begin with.
__________________
CX

Y'ALL NEW VISITORS READ THIS HERE!
cx is offline   Reply With Quote
Reply

Stonetooling.com   Tile-Assn.com   National Gypsum Permabase


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Floor and Decor as a resource MattOBrien Professionals' Hangout 37 10-18-2017 03:40 PM
Help finding the appropriate resource jshusc Tile Forum/Advice Board 15 09-27-2016 05:04 PM
CRM (customer resource management) eblumer Computer Training 8 09-13-2013 02:52 PM
Online marble resource? greg98 Tile Forum/Advice Board 2 08-26-2010 04:19 PM
Resource for walk-in shower Dave8fire Tile Forum/Advice Board 2 06-15-2006 04:56 PM


All times are GMT -6. The time now is 02:01 PM.


Sponsors

Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2018 John Bridge & Associates, LLC