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Unread 12-31-2020, 07:47 AM   #1
SilverBullet07
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Marble Floor Tile

I am tiling a 6x5 half bath. My better half wanted marble so we choose a 6x12 size.

We have engineered floor trusses (yellow Pine) and 1.5" of plywood as subfloor.

The bathroom is at the end of the truss with Concrete Walls that they are setting on.

I plan to use Ditra as un-couple membrane.

The Original floor had 2x2 ceramic tile laid straight onto plywood. No cracks or grout issues for 32 years.

I don't know what the truss deflation would be but do you think I should be ok?
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Unread 12-31-2020, 10:55 AM   #2
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Not enough info on the trusses to give you an opinion that isn’t ripe with speculation. Do you have any other info on them?

In the mean time, I’ll ask: is your marble polished? I ask because it is extremely soft and not very durable. A single spot of toilet bowl cleaner can quickly etch it permanently. I would suggest looking into polished porcelain that looks like marble. It’s much, much more durable and doesn’t have the requirement of a super stiff floor that natural stone does. However, polished porcelain is susceptible to staining and likely will benefit from sealing if there’s a danger of potential staining liquids in the bath.

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Unread 12-31-2020, 11:25 AM   #3
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She is going with honed marble. We know all about the issues but I have heard how much she wants it for 10 years so she is going to have to live with the issues. She wanted it in our last remodel and she was talked out of it and I have lived with that for 10 years.
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Unread 12-31-2020, 11:56 AM   #4
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Hi Harold. Keep in mind that the framing for a stone floor needs to be twice as stiff as for a porcelain floor. That's the reason Bubba asked about the trusses. So, it's not just a matter of replacing the tile with stone and it'll be problem free like the first floor. A stone floor also requires two layers of plywood, not just one layer like tile does. Of course you can install the stone with what you have but we're just telling you what the tile industry guidelines are and how we would do it.
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Unread 12-31-2020, 12:38 PM   #5
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Thanks. I do have two 3/4 in plywood nailed together every 4 inches. This is on top of the trusses. I'm not sure about the information on the trusses. I guess it is good the room is on the end supported by concrete wall maybe less deflection.

What any information I can provide help determine if the trusses are sturdy?

They are 2x4 open 20" high and on 24" centers.
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Unread 12-31-2020, 08:57 PM   #6
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What is the spacing and unsupported span of the joists, Harold?

The only real way to determine the design deflection of that kind of joist is to consult the manufacturer's specifications. To do that you've gotta know the manufacturer, of course. You see any brand names stamped anywhere on them? Or a plastic tag stapled to one?
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Unread 01-01-2021, 11:12 AM   #7
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Here is what I have under the bathroom floor. The 1/2 bath is 6x5

(Double side by side) truss 2x4x25 right wall
2x9x10’ joist. Tape measure measures 9” middle floor
(Double truss side by side) 2x4x25 left wall
All 24” center

Both double trusses are supported at 10’ with a wall closest to bathroom.

I found a stamp on the trusses if this tells anything.

Thanks for looking and helping.
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Unread 01-01-2021, 11:25 AM   #8
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Quote:
Originally Posted by Harold
(Double side by side) truss 2x4x25 right wall
2x9x10 foot. Tape measure measures 9” middle floor
(Double truss side by side) 2x4x25 left wall
All 24” center
'Fraid I find that a bit baffling, Harold. You're saying your trusses are 9 inches tall and spanning 25 feet unsupported, perhaps? Or maybe they're 25 inches tall?

Perhaps a photo from farther away showing the truss situation?

The grade stamp is for the lumber, not the truss. Says your lumber was graded by the Southern Pine Inspection Bureau and is of very good grade and species and was kiln-dried to 15 percent moisture content, all of which is common in truss manufacture. But it tells us nothing at all about the engineering of the truss in question.
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Unread 01-01-2021, 01:26 PM   #9
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No the 2x9x10 is a joist between the 2 trusses. The trust is 2x4x24” with cross members. Photo was in a post above #5 post
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Unread 01-01-2021, 01:56 PM   #10
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Saw that photo, Harold, was wondering if you had one from farther away showing more of the general layout that might help me understand some of your description. Like the 2x9x10. Is that 2 by 9 inches by 10 feet, perhaps? And how does that fit in with 2x4x24" trusses and what is meant by "cross members?"

Trying to get a better feel for this floor structure. If no photos available, perhaps you could make us a simple drawing?
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Unread 01-01-2021, 04:16 PM   #11
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The joist is a 2”x9”. One end to the other is 10’.

The joist is between a double truss on the left and a double truss on the right. All 24” apart on center.

The cross members I stated was about the truss 2x4 going diagonal in the truss.

The bathroom sets above these 4 trusses and 1 joist.

Hope the photos can help you understand what I am trying to say.

It is hard to capture the other set of trusses on the other side of joist but you can see it if you enlarge the photo some.
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Unread 01-01-2021, 07:51 PM   #12
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Some interesting framing.

I've never encountered those open-web trusses used top-bearing that didn't have doubled top chords at the end and other special connection down to the bottom chord, but that doesn't mean it can't be done. I've also never encountered such trusses used doubled, either.

It appears that the single 2x10 joist was used to accommodate the drain plumbing in that area. That sound like what you see going on there, Harold?

In any case, here's what I expect you've got to work with. Those engineered joists are almost certainly not designed to meet the required L/720 deflection criterion for a natural stone floor installation. Given the 25-foot span, I would expect them to be designed for at least L/480 as that's a commonly expected standard to ensure a proper "feel" in floors with long joist spans such as that. If you're content to install your natural stone over what you've got, you might be fine. Or not. There is at least one manufacturer of tile installation products who will accept that joist deflection with natural stone if you use all his products in the method prescribed.

Your subfloor, if both layers are correctly and differently installed, would also be satisfactory for the stone installation if an acceptable tile substrate were also installed.

Were it mine, I'd likely install the stone tile. If, again, all the ifs above turned out to be true. If it were for a customer, I might still do it, but I'd use the package of installation materials prescribed by Laticrete for their warranty over joists with L/480 deflection. But then I'd need to find a way to prove the joists did actually meet that requirement. And I'd still worry about the top-bearing ends on those trusses that don't look to me to have been designed for that application.

It's all so complicated, eh?

My opinion; worth price charged.
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Unread 01-01-2021, 08:09 PM   #13
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Well this is really what she wants. It is a small space so if it breaks up I guess she will learn her lesson. Sometimes if you can’t listen you got to feel.....

So many times she has been warned. So we will give it our best effort and hope for the best.
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Unread 01-01-2021, 08:40 PM   #14
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If it fails, just blame it on me, Harold. You don't have a geographic location in your User Profile (frequently helpful), but we'll guess I'm far, far away and she can't find me, but still she'll have somebody other than you to yell at, eh?
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Unread 01-05-2021, 01:12 PM   #15
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Question on tile layout.

Horizontal floor measurement is 55 1/4"

My tile is 6" wide. I'm using a 1/8 grout joint.

If I use 9 tiles with 1/8 grout space that puts me at 55 1/8", That leaves me to make up 1/8" for the correct 1/4" off the wall spacer.

Would it be acceptable for me to make up the 1/8" in a couple unseen grout joints? One wall is really not seen. It is under the vanity and behind a toilet. So if I take the last two runs and make it 3/16" grout line, I can add an additional 1/8".
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