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Unread 10-01-2019, 05:59 AM   #16
ss3964spd
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That's correct, Zane, you basically slather mortar onto the entire area you wish to water proof, and then the water proof membrane (Schluter, Durock, etc) is set into the fresh mortar. The mesh tape set in mortar is no longer necessary because the membrane does the same thing.

However, as with all water proofing methods, there are certain aspects of sheet membrane installation that could catch the inexperienced, or unaware, off guard; such as applying mortar to a rather large area then getting the membrane hung and embedded before the mortar skins over. Best to know the ins and outs before jumping in.
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Unread 10-01-2019, 09:53 AM   #17
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Excellent! Thank you Dan! And this is the preferred method vs. red guard and the like to get a flatter surface I take it. Makes sense!

A couple questions then regarding the surface membrane...

With Kerdi, do you use unmodified thinset for both sides of the membrane? This isn't an issue with LFTs?

Do you wrap it right around the corners as one continuous sheet?

Cx mentioned a preference for the Durock membrane in another thread. I can get Kerdi for less. Is there a substantial difference?

And finally, since I did a conventional pan, how does the wall to pan detail look? Just bring the surface membrane flush to the bottom of the durock, which is 1/2" off the pvc pan liner, and embed it in the mud bed too?

Thank you all so much! I guess I'm glad I asked a stupid question to get on the right track for the bigger issues here...
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Unread 10-01-2019, 03:58 PM   #18
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1. Schluter recommends the use of unmodified thinset mortar with their products. Everyone else, including the manufacturer of your CBU, requires the use of modified thinset mortars. You'll have much better luck with a modified mortar, 'specially on your first time out. If you can get access to Ditra Set, which is technically un-modified, you'll find it handles much like a modified mortar.

2. It's possible to do that, but I'd not recommend it for your first try with those products. I prefer to pre-cut pieces to hang vertically on the walls.

3. I much prefer the Durock Shower System membrane as it's a good deal thinner than Kerdi, making for much less build-up in the overlaps, and I find it easier to handle, crease, and bed into the thinset mortar. If you use Kerdi, I recommend you buy Kerdi Band and use it for all your seams. With Durock, overlapping the sheets works just fine. You can do that with the Kerdi, too, but you'll have more build-up.

4. Cover your walls first and bed the bottom of the covered CBU in your final mud bed.

My opinion; worth price charged.
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Unread 10-02-2019, 10:24 AM   #19
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Thank you thank you thank you!

I'm sold. Durock Membrane it is.

Hopefully just a couple more questions then...

1. If I use LFT Thin/Medium Set to hold the tiles, should I apply the same mortar behind the membrane? It would make sense to me that the assembly is as strong as the weakest link, but I have a bag of standard versabond modified from bonding the mud bed to the slab. Bad idea to use it behind the membrane? Or alternatively for the floor mosaic tiles directly on the mud bed?

2. How thick should the thinset be between laps? And behind the membrane, is a 3/8" notch trowel the right tool?

3. Durock sells a 5" strip for corners etc. I need a 36"x50' roll of membrane but will have a lot left over. Can I cut my own strips from the 50' roll or is it different material.

4. The mixer valve seal is round. I have a Delta R10000 valve which has a square rough in guide. Again, can I just cut my own template out of a small section of fabric?
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Unread 10-02-2019, 10:45 AM   #20
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1) You probably don't want to use the LFT for any of the membrane. From what I've read here the aggregate in the LFT is somewhat larger than, say, regular Versabond so the overlaps will be thicker. I used VB for pretty much everything in my recently finished bath; membrane to wall, membrane to membrane, tile to membrane, CBU to ply.

Though I did use some VB LFT I found no benefit, likely because I don't really know what I'm doing or looking for, so went back to regular VB. My wall and main floor tile are all 12X24, and the shower floor is basically a 2X2 mosaic. Only other exception was using Flexbond for the glass accents.

2) How thick, or how wide? The Durock band is 5" IIRC so you only need the mortar width to just wider than 5", but it certainly won't hurt if it's wider. Thickness wise, you'll want to mix your mortar thinner than normal which will make it easier to smooth once the membrane is up and will help keep build up under any overlaps to a minimum. The USG site specifies the notch size, but I think it's 1/8X1/8 square or 3/16X3/16 V.

3) The membrane and the band are the same material. no problem with cutting 5" wide strips from the larger roll.

4) That's what I'd do.

Depending on your layout you might benefit from the pre-formed inside and outside corner pieces that both Schluter and Durock sells. I was advised to use the Kerdi corners, because the Durock corners are made from a thicker material than are the Kerdi corners. Thicker means more build up. I had both on hand and the Durocks' are definitely thicker.

If that bag of VB you have has been opened and sitting for more than a few weeks I'd chuck it and replace with new.
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Unread 10-03-2019, 09:21 PM   #21
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Thank you Dan!

VB it is then for the membrane, but yes I guess I’ll have to get a new bag(s). It’s been opened for months.

So just the basic modified VB for those big tiles? Maybe I’ll try to dig up the PSI ratings for comparison. Thanks for the tip on flexbond though as I do have some glass accents planned as well. And thank you for the trowel info - I’ll try to confirm but that makes more sense.

I was planning to get some prefab corners. No problem mixing kerdi and Durock membrane?

Do you buy the shower head pipe surround too or just cut a round hole in a piece. It looks like it has a little rubber gasket to seal around the pipe...
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Unread 10-04-2019, 06:52 AM   #22
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You can certainly use the LFT VB for setting the tile, Zane, but I'm simply not experienced enough to discern any difference using it over regular VB.

In the grand scheme of things mortar just isn't expensive enough to risk using a bag that's been sitting around open for more than maybe a month. I tossed several partial bags, onna count I am a terribly slow tiler.

If my over 48 hour shower pan flood test is proof, it appears to be no problem using Kerdi corners on Durock membrane.

I did not bother with sealing the shower head pipe at all. The original head pipe simply went through a hole in the drywall, covered by a plain 'ole escutcheon. When I demo'd the almost 40 year old shower there was no evidence of water damage to the drywall up there. I raised the height of the head pipe in the new shower by at least 6", and now tile goes to the ceiling (well, almost, it stops at the bottom of the crown). Same set up, just a hole in the tile, screw the pipe in, finish with the escutcheon.
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Unread 10-08-2019, 11:14 AM   #23
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Excellent! Thank you Dan!

I orderd the Durock membrane, Kerdi corners and an 1/8" square notch trowel. I'll post back when the next conundrum inevitably arrives, but until then thank you all so much for the help!
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Unread 10-27-2019, 11:57 AM   #24
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I've had a coupled more questions come up...

First, I bought a bag of Mapei Ceramic Tile Mortar to adhere the Durock membrane to the Durock CBU because it met one of the ANSI standards listed for the membrane.

Now that I read a bit more, it seems this was previously called "Ultraflex I" and is not recommended on a number of threads here.

I already bought Versabond LFT for the actual tile setting, so my other concern was with mixing brands (though separated by the membrane).

Maybe best to just go get a bag of normal Versabond for behind the membrane? Or just use the LFT everywhere?

As for trowels, 1/2" square notch seems standard for LFT, but was reading here that some prefer 1/2x1/4 U notch so the ridges are easier to collapse. I've spent an ungodly amount of time leveling all the CBU so I think slightly less thinset would do just fine. I also already have a 3/8" square notch. What would y'all suggest if the flatness of the backer board is in spec?
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Unread 10-27-2019, 12:17 PM   #25
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Quote:
Originally Posted by Zane
Maybe best to just go get a bag of normal Versabond for behind the membrane?
I would.
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Unread 10-27-2019, 12:28 PM   #26
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For the trowel, Zane, I would try the 3/8" SQ notch first, IF the tiles you are setting are pretty flat. I used a 3/8" slant notch for mine and it worked very well I thought. Use the 3/8, set a tile, then pull it off to see what the coverage looks like.
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Unread 10-27-2019, 12:55 PM   #27
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Ok awesome! Thank you both! Versabond it is.

So lay it on the 3/8 troweled thinset without back buttering, pop it off and check for coverage? Would it be worth doing the same test with the tile back-buttered? I suppose if there are spots without coverage without the back-buttering, then it probably means bigger notch size regardless.

Seems like unless my eyes are lying, if I've got the CBU leveled to 1/16 over 2' and 1/8" over 8' (no 10' spans on this shower), then a 3/8 trowel should give a pretty hefty margin of error.
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Unread 10-27-2019, 01:07 PM   #28
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Being a novice I damp sponged and back buttered every single piece of tile I set in my recent bathroom job, except the 2X2 mosaic on the shower floor. But I also lean towards over-kill, don't do this for a living, and clearly had no finish-by date.
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Unread 10-27-2019, 07:27 PM   #29
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Yeah ok thanks! I too intend to back butter, but was just wondering for the coverage test. I think I will be fine with the 3/8 trowel.
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Unread 10-28-2019, 09:12 PM   #30
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So yet another question came up. When I mud the curb, is there a time window in which I have to install tile (before full cure)?

As I recall for the mud bed, you have 24 hours to install the floor tile or you must wait 30 days. Is it the same with the curb or is this just for dry-pack?
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