Underlayment Under Marble - Flooring - Contractor Talk

Underlayment Under Marble

 
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Old 04-14-2015, 07:55 AM   #1
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Underlayment Under Marble


Hey what's best plywood under marble. I'm reflooring a 12x15 bathroom. Hardi board will be used. Also can wire floor heat be used under marble?
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Old 04-14-2015, 01:52 PM   #2
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Re: Underlayment Under Marble


Typical framing won't handle a stone tiled floor. If you have room to raise the floor height, that might help. Shoring up the framing from below is optimal.

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Old 04-14-2015, 02:01 PM   #3
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Re: Underlayment Under Marble


would depend heavily on the thickness of the marble. How thick are the beams?
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Old 04-14-2015, 02:21 PM   #4
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Re: Underlayment Under Marble


The thickness of the tile is not relevant. The structure of the framing is.
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Old 04-14-2015, 03:57 PM   #5
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Re: Underlayment Under Marble


What is supporting the floor? 2x8's , I Beams, Open web trusses? Ands at what centers? 16", 19.2", 24"? You need to make sure the installation we be safe first...
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Old 04-15-2015, 12:07 PM   #6
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Re: Underlayment Under Marble


Thanks guys. This is a remodel, everything is down to 2x4 walls, and true 2"x8" joist. I believe they're 19"C. I can add more joist NP, however I couldn't add more beams. The span is about 12'. I have some play room on the height.
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Old 04-16-2015, 10:22 AM   #7
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Re: Underlayment Under Marble


Found thishttp://inspectapedia.com/BestPractices/Best_Kitchen_Bath10.htm

Subflooring Requirements for Tile Floors

To meet TCA stiffness requirements, floor framing should be no more than 16 inches on-center with minimum 19/32 -inch plywood subflooring. Upgrading to 23/32- inch plywood will stiffen the subfloor by almost 80% and provide a more solid feeling floor. The subflooring should be level to 1/8 inch in 10 feet. (TCA specs now permit 1/4 inch in 10 feet, but this can be problematic for the large tiles popular today.)

To avoid tile cracks caused by tight-fitting plywood joints, it is best to use square-edged subflooring under tile and leave an 1/8-inch gap between sheets (unless the setting material specifications require tight joints). Lay the plywood with its long dimension across the joists and use solid blocking at all open joints.

Two-Layer Subflooring System for Ceramic Tile Floors

To meet the stiffness requirements for natural stone floors may require two layers of subflooring screwed and glued together, with the upper layer serving as the underlayment.

Two layers of 19/32 inch plywood glued and screwed together on 6-inch centers is several times stiffer than a single layer (and over four times as stiff as a single layer of 23/32-inch plywood). Offset the upper layer so the joints do not line up with the joints in the lower layer or the joists.

Also, screws in the upper layer, which serves as underlayment for the tile, should penetrate the subfloor only and not the joists. Use underlayment- grade plywood or plywood rated C-C Plugged or Plugged Crossbands, with a smooth face and no voids.
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Old 04-16-2015, 07:13 PM   #8
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Re: Underlayment Under Marble


Quote:
Originally Posted by music9704 View Post
Found thishttp://inspectapedia.com/BestPractices/Best_Kitchen_Bath10.htm

Subflooring Requirements for Tile Floors

To meet TCA stiffness requirements, floor framing should be no more than 16 inches on-center with minimum 19/32 -inch plywood subflooring. Upgrading to 23/32- inch plywood will stiffen the subfloor by almost 80% and provide a more solid feeling floor. The subflooring should be level to 1/8 inch in 10 feet. (TCA specs now permit 1/4 inch in 10 feet, but this can be problematic for the large tiles popular today.)

To avoid tile cracks caused by tight-fitting plywood joints, it is best to use square-edged subflooring under tile and leave an 1/8-inch gap between sheets (unless the setting material specifications require tight joints). Lay the plywood with its long dimension across the joists and use solid blocking at all open joints.

Two-Layer Subflooring System for Ceramic Tile Floors

To meet the stiffness requirements for natural stone floors may require two layers of subflooring screwed and glued together, with the upper layer serving as the underlayment.

Two layers of 19/32 inch plywood glued and screwed together on 6-inch centers is several times stiffer than a single layer (and over four times as stiff as a single layer of 23/32-inch plywood). Offset the upper layer so the joints do not line up with the joints in the lower layer or the joists.

Also, screws in the upper layer, which serves as underlayment for the tile, should penetrate the subfloor only and not the joists. Use underlayment- grade plywood or plywood rated C-C Plugged or Plugged Crossbands, with a smooth face and no voids.
Where did this info come from? While a second layer of ply is required for natural stone tile, I certainly wouldn't bond directly to this second layer. A more suitable underlayment should be used in addition to a second layer of plywood.
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Old 04-16-2015, 07:55 PM   #9
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Re: Underlayment Under Marble


AND....

none of that addresses the insufficient framing.
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Old 04-16-2015, 08:07 PM   #10
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Re: Underlayment Under Marble


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Originally Posted by angus242 View Post
AND....

none of that addresses the insufficient framing.
This is true. A simple deflection calculator tells the story every time.

Basically, the maximum unsupported span for a 2x10 is 10 feet, for a 2x12 it's 13 feet. Engineered joists, you need to consult the manufacturer.
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Old 04-16-2015, 08:31 PM   #11
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Re: Underlayment Under Marble


He's talking about 2x8's with 19.2" OC.....
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Old 04-16-2015, 09:05 PM   #12
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Re: Underlayment Under Marble


Quote:
Originally Posted by angus242 View Post
He's talking about 2x8's with 19.2" OC.....
Craaaack!
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Old 04-17-2015, 05:47 AM   #13
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Re: Underlayment Under Marble


Quote:
Originally Posted by angus242 View Post
He's talking about 2x8's with 19.2" OC.....
I missed that part. That doesn't even make it for ceramic. Even sistering every joist doesn't quite make it. You would need to double sister every joist to make it suitable for natural stone.
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Old 04-18-2015, 12:56 PM   #14
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Re: Underlayment Under Marble


Quote:
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I missed that part. That doesn't even make it for ceramic. Even sistering every joist doesn't quite make it. You would need to double sister every joist to make it suitable for natural stone.
I was answering a question about the joist. Yes they are old true 2"x8" 19 oc. I stated that I could add joist, (sister, 12" oc) whatever it takes. I can't add a beam under the joist though. Again, a remodel and everything is down to 2x4 walls and joist. As far as the type of stone, I'm not for sure, probably 12" marble. I do plan on using hardie board or concrete board. The page was inspecitda (something like that) I posted the link for the page, it didn't hyperlink tho.
I'm not trying to argue, I just wanted to know the best, safest way. I appreciate all the help.
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Old 04-18-2015, 01:03 PM   #15
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Re: Underlayment Under Marble


Quote:
Originally Posted by music9704 View Post
I was answering a question about the joist. Yes they are old true 2"x8" 19 oc. I stated that I could add joist, (sister, 12" oc) whatever it takes. I can't add a beam under the joist though. Again, a remodel and everything is down to 2x4 walls and joist. As far as the type of stone, I'm not for sure, probably 12" marble. I do plan on using hardie board or concrete board. The page was inspecitda (something like that) I posted the link for the page, it didn't hyperlink tho.
I'm not trying to argue, I just wanted to know the best, safest way. I appreciate all the help.
It's cool bro, I didn't think you were trying to argue, neither am I. Just having a friendly discussion with fellow tradesmen.
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Old 04-18-2015, 01:07 PM   #16
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Re: Underlayment Under Marble


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I'm not trying to argue, I just wanted to know the best, safest way. I appreciate all the help.
The best way to install to not get a failure is....


don't install the marble.

There is no arguing, the marble is absolutely the wrong material for this scenario. You will still have to beef the hell out of the floor just to install ceramic. Marble is not an option. But what the heck do I know....
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Old 04-18-2015, 01:42 PM   #17
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Re: Underlayment Under Marble


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Originally Posted by angus242 View Post
The best way to install to not get a failure is....


don't install the marble.

There is no arguing, the marble is absolutely the wrong material for this scenario. You will still have to beef the hell out of the floor just to install ceramic. Marble is not an option. But what the heck do I know....
If you were able to beef up the structure to meet L/720, why would marble not be an option?
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Old 04-18-2015, 01:46 PM   #18
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Re: Underlayment Under Marble


You could. I'm making the assumption paying for what it would take to make that trampoline of a floor L/720 not an option. Even adding 2x8 to be on 12" OC isn't close enough to install marble.
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Old 04-18-2015, 02:51 PM   #19
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Re: Underlayment Under Marble


I'm getting a better picture here. I took a look at deflection calculator. Now if I just knew what dense selection numbers meant. It looks like I'm pretty close with 12" oc. Southern pine.
Also, sorry, its all good. I've been under the house fixing someone's mess......ugggg
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Old 04-18-2015, 04:20 PM   #20
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Re: Underlayment Under Marble


Quote:
Originally Posted by music9704 View Post
It looks like I'm pretty close with 12" oc
Actually, you're not.

2x8; 12" OC, 12' span is NOT close.

Last time I'll say it. In this case, marble is not the material to use.

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