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Unread 01-07-2004, 03:10 PM   #1
Rob_from_NC
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Proper subloor prep for 18x18 Travertine Tile installation

First time poster here. Have read through a great deal of this forum and it is very useful, thanks for all the expertise sharing!

I am preparing a subfloor for a large travertine (18x18") floor tile installation (my own house). The joists are 16" oc and supported every 10' feet with a beam and concrete piers. The first layer of flooring over the joists is 1x6 boards running diagonal across the joists. There is a single layer of tarpaper over the diagonal boards. I have removed the layer of pressboard carpet undelayment which covered these diagonal boards, and am planning on replacing it with a layer of 23/32 sturd-I t&g plywood giving me roughly an 1.5" thickness overall. I am then planning on using either a 1/4 inch durarock or ditra as the uppermost underlayment. I was planning on using the Masterblend modified thinset (white) both below the ditra/or durarock and between that layer and the travertine. My questions are as follows:

1) is it acceptable practice to screw the 22/32 sturd-I panels to the 1x6 diagonal boards, leaving the tarpaper in the middle? I have read reference here of gluing and screwing the second layer of subloor to the first, but the diagonal boards have small spacing between them and (it would be preferable for me to leave the tarpaper as a barrier since there is a dirt crawl space below)?

2) Any thoughts as to which is preferable in a travertine installation - ditra or durarock (or other cb)? And why one over the other?

3) Is there a recommended thinset to set the ditra/cb. Was planning on using a modified thinset for both that and the travertine. Don't know if this is necessary or advisable. Have read elsewhere of using a 'quickset' bed for the travertine?

Finally, with a 1/16 grout line, are there any pro tips or tricks to ensuring the levellest possible floor? How about levelling each individual tile, do you recommend thinset on the floor first, then back-buttering the tile, just thinset on the floor or just backbuttering the tile? Any advice would be greatly appreciated.

P.S. the room is 19' wide by 36' long

Thanks,

Rob
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Unread 01-07-2004, 03:26 PM   #2
Sonnie Layne
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Hi Rob, welcome to TYW.

Before the others get here, we'd like to know how far apart the joists are supported, so we can use the deflectometer (upper right hand corner of this page) and determine what your deflection is. Your floor, that is We don't get that personal on first posts 'round here.
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Unread 01-07-2004, 03:34 PM   #3
bbcamp
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As long as your joists are 2x10 or bigger, you're OK for stone. 2x8s are good for ceramic tile.

1) make sure your planks are firmly attached. Adding new screws won't hurt. You can leave the tarpaper and screw the new plywood to the planks.

2) Don't have a preference, maybe the pros will.

3) Unmodified under the CBU, modified over. With Ditra, modified on both sides.

If you want 1/16" grout lines, using SCL to level the floor, or using a mud bed may be a must. (the pros will tell you for sure, but I'll tell you that this will be a b***h)
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Unread 01-07-2004, 03:54 PM   #4
Rob_from_NC
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Thanks Sonnie,

The joists are 2x10 syp, spaced 16" on center. They tie into a triple 2x12" band every 10 feet , with the bands being supported by concrete piers, or the outer foundation wall. So if you picture the room as a large rectangle, looking at it from above, the joists run horizontally (from long end of room to long end), and tie into the the 2x12 bands (running vertically - short end of room to short end) every 10 feet. Hope that clarifies things.

ROB
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Unread 01-07-2004, 04:02 PM   #5
Sonnie Layne
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Sure does, you're good to go. Just wanted to make sure.

Don't level each individual tile, the whole thing's gotta come out as one unit, and no torpedo level I know of can be read that well. Level across 3 or 4 at a time. Back knifing/buttering would be advised. Clean up your squeeze out as you go. It's not gonna be the easiest floor to set, but you'll be OK. Take your time, you'll need some. Take your Advil, you'll need some of that, too.
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Unread 01-07-2004, 04:05 PM   #6
David Taylor
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Hi Rob and welcome.

To level the tiles, you should get the floor as flat as possible before laying any tile. Any small differences can be made up with the thinset used for laying the tile.

BB's right about the thinsets to use. You're obviously not going to get the marble laid all in one day, otherwise I'd suggest an unmodified thinset over Ditra. An unmodified thinset would only take one day to dry before you'd be able to grout. With marble (and it being 18"), modified mortar would take three days to dry before you could grout.

Ditra has many advantages over CBU. First off, it's much easier to install. You could have that whole area done in one day and not have any dust on you afterwards. With CBU.... well, I'll let the other people on here tell you what it's like loading 47 sheets of it (over a half ton) in your truck, getting it into the house without damaging anything, cutting and installing it.... etc.
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Unread 01-07-2004, 07:56 PM   #7
John Bridge
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Hi Rob,

Ditra's definitely the way to go.
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