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Unread 10-19-2011, 12:38 AM   #1
Maren
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Marble over ... over planks

Hi, folks. About to embark on installing a crazy-quilt pattern of myriad marble tile (12", many different colors), and thought I'd bounce the tentative plans around the JB forum. Original subfloor is diagonal planks (up to 12" wide, and squishy in a few spots where knotholes are near board edges; might reinforce those spots from below) over 2x10's 16" OC. Planning to add a layer of plywood (screwed with deck screws? any fun tools to calculate how many?), have been advised that 1/2" would be sufficient (do you think it would?). Also, how important is it that the plywood's face-grain is always perpendicular to the joists over a plank floor? The space is small and sort of complicated in shape (I have seen the advice about keeping joints off of joists; good tip!).

Then modified thinset (brand recommendations welcome). Then Ditra (for height and for crack insurance, vs. Hardiebacker), maybe Kerdi-band if it's available. Then hmmm, the marbles are really multifarious: reds, pinks, yellows, whites, near-blacks, some dark greens, some mixed colors. Should we be using epoxy mortar under the tiles? Again, I welcome brand recs.

I've also seen some sealing stuff that one mixes in with powdered grout, in place of water... is that stuff worth using?

Thanks for any thoughts you have!

Be well,
-- Maren.
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Unread 10-19-2011, 03:39 AM   #2
Tool Guy - Kg
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Hi Maren,

Neat idea. But...

Your tile is most likely a myriad of thicknesses and facial dimensions. If you're willing to fight lippage due to the different thicknesses with varying amount of thinset (not easy)....and are okay with not having consistent grout width joints, say so and we'll get on with the technical stuff.

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Unread 10-19-2011, 06:33 AM   #3
Maren
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lippage

Yup, I'm figuring on a little lippage fighting. I figure a rubber mallet and a straightedge ought to do the trick. And I'll make the grout spaces wide enough to not look ridiculous for facial variations. Thanks for the check-in!

-- Maren.
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Unread 10-19-2011, 07:25 AM   #4
tileman2000
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Instead of fighting lippage, you should look into the TLS,Raimondi or Lash leveling systems.
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Unread 10-19-2011, 07:48 AM   #5
bbcamp
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Check the floor joists with our Deflecto tool.

I'd consider 5/8" or thicker plywood, considering your planks are not T&G and some are in poor condition. Fasten with screws every 6 inches along the edges and in the field, unless you stay with 1/2" plywood. Then, use a screw every 4 inches along the edges, and 6 inches in the field.

I would think epoxy will get expensive if you do the entire floor. Do you have enough tiles that you can eliminate the green ones, and any others that require an epoxy adhesive? At the very least, skim coat the backs of those that do require epoxy, then set them in thinset or medium set mortar.

Have you considered "rectifying" the tiles that are oversized? That way, you could keep your groutlines 1/8" or less and use unsanded grout.
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Unread 10-19-2011, 09:02 AM   #6
Maren
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leveling

Yes, I had seen some of those leveling systems, and while they look great for uniform tile, I don't see how they would work for varying thicknesses. (my variations aren't major but they are there). Does the top pyramid/cone/wedge push hard enough to deform the bottom of the clip, or does the difference just get cut in half? And does whatever remains in place (I don't see how the whole clip could be extracted) weaken the grout the way leaving spacers in would?

Thanks!
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Unread 10-19-2011, 09:27 AM   #7
Maren
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Bob -- I did do a DeflectoCheck. I think it's OK -- the joist span was originally 14' but we put a 2x12 crossbeam under the middle (attached to a wall below) because at the time I was considering flagstone (since used up outside), so the largest span is really 8'. Sistering would be difficult due to obstructions (including said wall, the main trunk heating ducts, and a bunch of electrical. Could perhaps do some of it in places.

Thanks for the plywood-thickness advice. I may go with 5/8.

> I would think epoxy will get expensive if you do the entire floor.
It isn't very big, not much over 100 sf...

> Do you have enough tiles that you can eliminate the green ones, and any others that require an epoxy adhesive?
The design would be way less interesting if I cut out all the reds as well... and indications of the susceptibility of different colors is all over the map. it seems better to play it safe if At the very least, skim coat the backs of those that do require epoxy, then set them in thinset or medium set mortar.

Have you considered "rectifying" the tiles that are oversized? That way, you could keep your groutlines 1/8" or less and use unsanded grout.

I haven't yet taken the tiles up from the design phase -- so I'm not sure how big of an issue this will be, as I didn't previously know which ones I'd be using before. If I do rectify (by which I presume you mean shave a bit off one or two sides), do you have suggestions as to method? Would a wetsaw blade deflect sideways for such small adjustments?

These tiles were samples from one or more stone suppliers, from our local building materials salvage place (I am big on reuse, and also love all the variety of natural stone). This also means that there are labels on the backs of some -- does a non-stone area like that matter, or should I scrape 'em all off (with the help of Citrasolv)? I'll certainly remove the Velcro strips from them as has 'em, if I can (I omitted most of those in the design).

Thanks much,
-- Maren.
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Unread 10-19-2011, 10:04 AM   #8
bbcamp
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I don't know if your saw blade will deflect too much to shave a bit off, but I think it worth it to find out. Sanded grout will eventually scratch the polish off the tiles.

Get rid of the lables, but I don't think I use a solvent other than hot water and a pH neutral soap. I wouldn't want to chance staining the tile or creating a bond breaking film on the back.
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Unread 10-19-2011, 10:21 AM   #9
dhagin
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The saw blade will deflect if you try to shave a blade width, for instance. Better to measure all the tiles and cut them maybe 1/4 less than the smallest. Experiment a little. You don't have to cut much, just need stone on both sides of the blade for support.

And I'd use a razor scraper for removing labels on the stone backs if the water doesn't work.
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Unread 10-24-2011, 03:43 AM   #10
Maren
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Update

To my relief, the marble tiles are all about the same size (a few are thinner but we can backbutter those more heavily). We have reinforced the squishy spots in the plank subfloor, and are about to put down a layer of 5/8" (well, 19/32") plywood. We'll use Ditra over a layer of Flexbond (modified, but that's what Schluter recommends over plywood), then unmodified Megabond. Undecided on whether to use Kerdiband along the seams and/or edges; it's an entry/ mudroom, which could mean snow coming in on boots, and there may be a sink down the line (it was the kitchen so there's plumbing already). I welcome thoughts on the Kerdi (and anything else, as always).

I plan to preseal the tops of the tiles that are less finished, more travertiney, and to mix the grout with a sealer-substance intended for that purpose (evidently a new practice). I gather that the polished marble tiles don't want sealing at all?

Thanks to everyone for offering advice and comments. Onward!
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Unread 10-24-2011, 04:42 AM   #11
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You can use Kerdi-band to waterproof the floor if you want. However, if you don't flash up the walls with Kerdi-band (or something) and seal all the floor penetrations and add a curb at each door way, you're wasting your time and money.

Pre-sealing is a good idea for stones that can be stained by the grout (marble is one), or if the surface is prone to collecting grout (travertine, et al). Test boards are good for finding out if this is necessary.

Unless the sealer additive is made by the same company that makes the grout, and is specifically stated in the grout instructions to use the sealer, I wouldn't do it. Grout is finicky enough as it is. Add to it another product that may or may not be compatible with it, and your risk goes off the scale. You do not have enough material to mess this up.
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