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Unread 11-24-2019, 09:00 PM   #16
Geoff CT
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My decision to do a mud job over the admittedly inadequate 1/2 inch subfloor was based primarily on how solid the original mud was. It was very solid (and hard to remove).

Yes, I would have expected the mud to embed really tightly into the metal lath (like it had with the original mud with the same type of lath, attached the same way). That concerns me too now that you mention it.

The job was completed Friday night, so it's been two days.

I mixed with water not the admix. The MAPEI instructions for mixing are as follows:
"Mix each 55-lb (24.9-kg) bag with 3 U.S. qts to 1 U.S. gal. (2.84 to 3.79L) of cool clean water, or with 3 U.S. qts to 3.5 qts. (2.84 to 3.3L) of MAPEI's Planicrete AC diluted in a 3-to-1 ratio of water to Planicrete AC."

I'm going to call the MAPEI Technical Services number Monday morning to get their take on this.
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Unread 11-24-2019, 09:05 PM   #17
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Geoff, did you pack the mud down before scraping it off? Sounds like the floor was a bit crumbly, which might indicate mud that's not tightly packed in. Even more so, since it wasn't embedded in the lath.
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Unread 11-24-2019, 09:07 PM   #18
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You'll wanna check also the manufacturer's date code on your bag of product, Geoff, to be sure it wasn't too old. Tech Services will tell you how to decipher the code.
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Unread 11-24-2019, 09:07 PM   #19
Geoff CT
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Bubba,

Mud is a bit over 3/4 inch in thickness per:

http://www.tiledoctor.com/blog/floor...ation-methods/
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Unread 11-24-2019, 09:13 PM   #20
Geoff CT
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Kevin,

Yes. I packed the mud down very well. If the mix was too dry (no one has suggested as such so far in this thread) then I could understand it not embedding sufficiently into the mesh.
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Unread 11-24-2019, 09:17 PM   #21
Geoff CT
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CX,

Good suggestion on the date code. I still have the bags, so I'll check the age of the product when I call MAPEI tech support Monday. I had to redo a grout job in the past due to old grout, so I guess this is a possibility.
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Unread 11-24-2019, 10:00 PM   #22
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FWIW, industry standards call for a mud bed over a wooden subfloor to be thicker than 3/4", closer to 1-1/4" or so. It might work, it might not. The thinner you go, the more it may rely on excellent workmanship. Cement is rated for full strength at 28-days, but attains a lot of that in the first few days to a week. Deck mud is strong in compression, but not in other ways. The lath will help to spread the load, but a thicker bed spreads it out further, helping to minimize deflections which can make things more stable.
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Unread 11-24-2019, 10:59 PM   #23
Geoff CT
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Jim DeBruycker,

Thanks for the info. This is consistent with the ANSI standard that I used to guide me. It's AN-2.6.1 ("Ceramic tile floors installed with Portland cement mortar") and more specifically subsections AN-2.6.3 and AN-2.6.4 (see attached). The latter specifies for residential installation a bed thickness of 3/4 inch minimum and 1 1/4 inch maximum.

This is from an older (1999) release of American National Standard for Installation of Ceramic Tile (ANSI A108, A118, & A136--1999). I don't have access to the current standard.

I chose the 3/4 inch minimum thickness to keep the finished floor height not excessively higher than the floor outside of the room that I'm installing the tile in.
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Unread 11-25-2019, 12:15 AM   #24
Davy
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We used to mud bath floors 3/4 thick all the time and never had any problems as far I know but they were over 1 1/8 plywood. Your thin plywood concerns me along with the patch in the floor. Those cold joints gives the floor a place to crack.

I will say that the Mapei 4 to 1 will get harder than the 5 to 1 mix I always use. I used the 4 to 1 once and other than the high price, I found it hard to work with when I had the water to my liking.
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Unread 11-25-2019, 12:25 AM   #25
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Geoff, I'll point out again that those specifications you're citing presume an adequate subfloor as indicated just a page or so further on in your ANSI A108, which you do not have. The 1 1/4" minimum mud bed Jim is recommending, with a welded wire reinforcing in the vertical center would be the better choice if you still elect to use your substandard subfloor. And it's very substandard because the minimum requirement of nominal 5/8ths" subflooring at least has available T&G edges, which your half-inch subflooring does not have.

You're pushing your luck pretty hard with what you're doing.

My opinion; worth price charged.
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Unread 11-25-2019, 12:17 PM   #26
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Hey there Geoff,

I'm very sorry to hear of your troubles with 4 to 1!
Give us a call so we can help you through this one; we will be here until 5:30 ET. Please make sure you have one of the bags in front of you when you give us a ring.
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Unread 11-25-2019, 05:06 PM   #27
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Not gonna spin my wheels anymore about the Houston Mud Method. All I'll say is that it definitely works and I and Paul have proved it time and time again.

Do it the traditional way if that floats your boat. Buggy whips worked well in their time as well......
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Unread 11-26-2019, 01:31 AM   #28
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Hi, Geoff. Sorry, but I just don’t see how 3/4” of mud on top of a scant 1/2” subfloor is not going to crack apart. To succeed would defy all the failures of similar installations I’ve torn out. I hope I’m wrong, though. I wish you the best.

And Laz, that method is suited for the Pro’s Hangout. But not for Advice Forum where industry standards and manufacturer’s instructions reign.
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Unread 11-26-2019, 12:35 PM   #29
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Point well-taken, Sir.
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