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Unread 12-01-2014, 03:42 PM   #1
dnsgrrl
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questions about threshold/support for marble - marble transition

I apologize if these questions have been asked and answered; I searched the forums but have not found my issue, so wanted to post it here for advice.

Older house (built in 30s) with a rear foyer of old marble in a patchwork pattern. Very small powder room (38in x 48in) connected, had linoleum tiles previously. We have removed the powder room flooring down to the original hardwood and it appears solid and fairly level. I have 12x12 marble tiles to put down.

The old tile in the foyer comes right up into part of the doorway and was clearly set right on the hardwood. I am concerned about how to transition to the new flooring unless I (gasp!) do the same - otherwise it is a big step up. there is no room for a standard marble threshold (and that would still leave the height disparity issue), and a wood reducer would look bad (marble - wood - marble). If I set right onto the hardwood floor, I would not need a threshold since the foyer has big grout lines - I could make a grout line be the transition.

1) when the actual space is so small that anyone can even stand on, is the use of wonderboard or the "ditra" underlayment critical, if I am concerned about height disparity, and the hardwood seems strong?
2) can a custom marble threshold/reducer be created by a marble fabricator place?
3) is there some other option I could use for this threshold that would make it ok to use the underlayment or the wonderboard?

I attached a picture of the threshold area.

I can accept that some supporting structure is necessary but I have no idea what to do for the transition, so I am basically stopped in my tracks on this. Appreciate any advice you might have.

thank you.
GiGi
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Unread 12-01-2014, 03:47 PM   #2
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Hello, GiGi. Welcome to the forum.

Maybe you could tell us how you plan to install the 12x12 marble you have. That would help us tailor our answers to your specific project.

In a nutshell, installing marble, whether it's a transition or a tile, would require something other than simply adhering it to the subfloor you have there.
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Unread 12-01-2014, 03:59 PM   #3
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Welcome, GiGi.

I could tease and tell you we have good new and bad news, but, unfortunately, there ain't really no good news.

First question is about the wood floor we see. Is that the only flooring in that area? Nothing under that? Those boards are fastened directly to the floor joists?

Let's get that information and see just how bad the bad news is fixin' to be.

[Edit] Looks like I dallied so long even ol' Kevin had time to squeeze in there.
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Unread 12-01-2014, 04:01 PM   #4
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Thanks Kevin,
I had been pondering the Ditra underlayment with whatever its thinset requirement is, or else 1/4" wonderboard screwed into the hardwood, and the marble/travertine mix sold by HD to adhere the marble tiles.

GiGi
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Unread 12-01-2014, 04:49 PM   #5
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I am now officially worried :-(

The hardwood appears connected directly to the joists below.

This house has suffered a lot of abuse in its day but the existing foyer floor shows no sign whatsoever of cracking.

So - what is the bad news ?
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Unread 12-01-2014, 05:02 PM   #6
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GiGi, the stone industry (MIA) standard is for the subfloor to be two layers of plywood regardless the joist spacing and also that the joist structure meet L/720 defelction standards rather than the L/360 required for ceramic tile. They will generally accept a sawn board subfloor as the first layer, although no one would be thrilled with the cut-up nature of what I see in your photo.

If your joist structure is adequate, which is rather unlikely, the very least you could do is add a second layer of nominal half-inch exterior glue plywood with no face of grade lower than C on top of your existing subflooring (after ensuring the boards are all well fastened) and then your tiling substrate.

The only way I know of not to use the plywood layer is to install a reinforced mud bed over the board subfloor. That requires the mud to be placed over a cleavage membrane and a minimum of 1 1/4-inch thick with welded wire mesh in the vertical center.

You will, of course, say that your old stone installation has done just fine and that you plan to do the new one the same way and that's entirely up to you. We can tell you only what the current industry standards require.

My opinion; worth price charged.
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Unread 12-01-2014, 05:16 PM   #7
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I was a little uncertain after I made the statement about the boards being directly nailed to the joists so I went down to the basement to see if I could get a shot of it. What i saw will make you happy - there are at least 2 layers if not three. I've added a few pics which are not great but which will show this, i think.

So under this powder room there are layers going in a few directions before reaching the joist. Sorry for the mis-statement.
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Unread 12-01-2014, 06:36 PM   #8
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GiGi, you would still need a layer of plywood over what you have there. No manufacturer of any tile underlayment allows their product to be installed over anything except plywood or OSB.

The other issue you may have is the deflection of the joists. For installation of natural stone, the joists have to be twice as strong as they would be for ceramic tile installation.

It's doubtful that they were built with natural stone in mind, but we can probably find out. What you'll need to know is the longest unsupported span of the joists in any area where the marble will be installed. You'll also need to know the grade and species of the joists, as well as the size, i.e. 2x8, 2x10 etc.

If you're uncertain on the grade and species, look for a stamp on the joists themselves. If you can post a picture of the joists, we might be able to help with that.
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Unread 12-01-2014, 09:56 PM   #9
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thanks. I will see about those measurements tomorrow. I sincerely appreciate the guidance here.

GiGi
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Unread 12-02-2014, 02:14 PM   #10
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there are steel girders every 8 feet across the basement ceiling , including below where this powder room is.

The joists measure 2 5/8 x 9 7/8

There are no stamps visible on any joist that i can see (and I can see most) but if I were to guess I would say red oak. They appear very similar to the ones in my last house, which is the same age, is not far from here, and for which my neighbor happened to send a sample off to his former professor (he was a structural engineer) for analysis (he wanted to shave 3/4 inch off each joist in his kitchen to accommodate radiant heating and a new floor, and the analysis showed he could have cut more had it been necessary).

The floor area under the powder has at least 2 layers and part of it looks to have 3.

Assuming this is strong enough, I am back to the original questions: if I use wonderboard on top of the hardwood, and tile the marble on that, What can i use for a threshold that is not off the rack?

And if you do not recommend wonderboard, what should i be doing (and what can i use for the threshold? ?

thank you for your patience.
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Unread 12-02-2014, 06:20 PM   #11
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GiGi, this may be the first good news in this thread.

If your joists are spaced at 24" or less, and they don't span any further than eight feet, I can almost guarantee you they are sufficient to support a stone installation. This is provided that they are in good shape and haven't been hacked up to run plumbing, electrical, HVAC, or other systems.

By the way, 2 5/8" is a very unusual joist width. Don't see that at all any more. You're very lucky.

If you do in fact have three layers of wood there on top of the joists, can you remove the top layer? Presuming the other two layers are adequate, you could add a layer of 1/2" ply, 1/4" cement board or other tile underlayment and be ready to tile. This might also solve some of the problem you have with the threshold and put the two floors at the same height.
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Unread 12-02-2014, 09:58 PM   #12
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I remeasured just to be sure and every joist I checked was 2 5/8 wide by just under 10 deep. The space between joists is 16 inches and there are none longer than 8 foot. The house appears to have been over-engineered at every turn so I suppose I should not be surprised if you say the joist choices were good too.

If I take out the oak flooring that you see in the first picture (it is not actually cut up, it just has some of the old (paper?) underlayment for the old linoleum still stuck to it) I have to do that from above, I assume? That would definitely help with the overall height issue and would insure the flooring was on super solid ground, I presume? So I would remove the oak and have 1/2" plywood and then do a thinset /wonderboard/thinset /marble? Or is there a better choice (this Ditra maybe) ? I've not done this on my own so I am a little worried I will miss something or make a bad choice.

thank you,
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Unread 12-02-2014, 10:04 PM   #13
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That's no problem, we're here to help.

What I wanted to verify is what you have underneath the oak flooring that we see on top. You can see the bottom layer from underneath, but that's about it until you do some demolition, or if there is a floor vent or other hole in the floor that you can see a cross-section of the rest of the floor.

If you have at least 3/4" of good subfloor, you can use 1/2" ply on top of it. 5/8" ply if the subfloor is on a diagonal. Verify that first, and then we'll move forward.

Or backward.
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Unread 12-03-2014, 07:33 AM   #14
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This will take me a day or more to accomplish. When it is up and I can see the substrate below I will take some photos and report back.

to be continued....

-GiGi
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Unread 12-03-2014, 08:14 AM   #15
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Gigi from your pictures it appears that there may be a plank subfloor laid on a 45 degree diagonal directly on top of your joists. This is fairly common in houses of the era yours was built. As you're removing the oak flooring try to leave whatever wood layers that sit beneath the oak undamaged (for now) since they might be useful later.
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