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Unread 02-13-2021, 05:10 PM   #76
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To the subfloor is sufficient, Matt.
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Unread 02-23-2021, 12:42 PM   #77
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Quote:
Originally Posted by cx View Post
In our Liberry you'll find a good article showing what I consider the very best method of installing that second layer.

CX, do I understand the diagram in the article you linked correctly to mean that 1) the second layer of plywood is set parallel to the first (both at a right angle to the joists), 2) that between the joists, the seams of the second layer are placed at 1/4” the joist span, and 3) the joints running the other way (the long ends of the sheets) are placed as far away from those same joints in the first layer as possible?
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Unread 02-25-2021, 10:42 PM   #78
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Is the aforementioned “cleavage membrane” roofing felt or some other material?

What about a similar situation but on a concrete slab? In that instance the lath can’t be stapled down... would one still use lath and a cleavage membrane or some other combination of materials?
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Unread 02-25-2021, 10:48 PM   #79
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Roofing felt is fine. Over concrete you customarily eliminate the membrane and lath and bond the deck mud to the concrete with a slurry of pure Portland cement or thinset mortar.

There is an unbonded reinforced mortar method over wood or concrete, but not normally used for a shower floor.

My opinion; worth price charged.
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Unread 02-25-2021, 10:57 PM   #80
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Ah, interesting. Slurry would be a thin layer of cement mixed very wet, which goes first, then deck mud? Do you have a link to a breakdown of that procedure?
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Unread 03-13-2021, 06:59 PM   #81
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Picked up a bracket and figured out how to carve out the framing so it would sit flush. No more wiggy pony-wall!
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Unread 03-21-2021, 08:10 AM   #82
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Circling back around and getting ready to install the roofing felt and lath for the mud pan... am I correct in thinking that it’s OK that the staples securing the lath will penetrate the roofing felt? (i.e. the felt is there to stop the subfloor from absorbing too much moisture from the mud as it cures but it’s kind of a secondary thing and obviously not a waterproof membrane so the staples are OK?)
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Unread 03-21-2021, 08:35 AM   #83
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It is as you describe. The staples are OK.

My opinion; worth price charged.
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Unread 04-16-2021, 07:31 AM   #84
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Getting ready to put down this mortar bed in the shower with Mapei 4-1. Instructions say to “prop up” the lath so that it is in middle of the mortar bed. I’ve already stapled down my lath (shoulda read the directions more carefully first!) so I’m wondering if it’s 100% necessary to remove the staples and figure out a way to prop this stuff in place, or if it’s acceptable to put the 4-1 down on top of the stapled lath?
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Unread 04-16-2021, 07:46 AM   #85
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Matt, if MAPEI actually tells you to put expanded metal lath in the vertical center of a mud bed, this is one time I will advise you to deviate from manufacturer's instructions. There may be some misunderstanding there, and they might be talking about a "reinforced mortar bed," which would require welded wire mesh in the vertical center, but for your application you want the expanded metal lath fastened over a cleavage membrane to the subfloor. Different types of mortar bed, different types of reinforcing material.

You do not want expanded metal lath in the vertical center of a mortar bed and I'll be very surprised to see MAPEI recommend such. I don't manufacturer mortar nor reinforcing mateiral, so that is, as always:

My opinion; worth price charged.
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Unread 04-16-2021, 08:16 AM   #86
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Mapei 4 to 1 instructions state this:

Floating or unbonded mortar bed:
...Lay out rolled or self-furred sheets of 2" x 2" (5 x 5 cm), 16-gauge, galvanized wire mesh throughout installation. Overlap the mesh by 2" (5 cm) and connect the sheets using wire ties.

So at least they aren't calling for metal lath for that method. They do say to refer to the proper TCNA guidelines for the mortar bed type....they could.be more clear though. Alas....follow CX's guidance here which I believe is for TCNA method F-145, if I'm not mistaken.

Matt,
There is also an old thread about the best water ratio for using that mud. Consensus was 2q 8oz of water per bag and that gave perfect consistency for dry pack.
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Unread 04-16-2021, 08:26 AM   #87
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OK, thanks, gents! Makes sense. That water ratio is significantly less than the 3-4 quarts/bag that Mapei recommends, but I think for this application I trust y’all’s advice and experience more than the bag.

Is that drier mix a function of the specific consistency needed for a shower floor as opposed to other applications?
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Unread 04-16-2021, 08:41 AM   #88
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When using that mud with more water, I believe it was said to be too hard to work when forming the shower floor.

https://www.johnbridge.com/vbulletin.../t-122231.html
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Unread 04-16-2021, 11:13 AM   #89
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Thanks for the link. This is a good thread. Is that 2.25 qt per bag ratio calibrated for a 55 lb bag of 4:1? Or a different amount?
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Unread 04-16-2021, 12:55 PM   #90
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Came out OK! Good slope, no bird-baths, pretty smooth.

Schluter says you can lay Kerdimat on a mud pan as soon as it’s safe to walk on. Mapei says the mud is OK to walk on after 16h. Does that seem like a long enough cure time before putting down a membrane? I thought I remembered reading a thread on here where someone recommended 48h, but I’ll go ahead and waterproof it tomorrow if that’s not a violation.

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