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Old 07-09-2018, 07:36 PM   #1
Justinfive10
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Justin's Hot Mop Shower

Hi, I wanted to piggy back off this question. What if the mortar bed is already laid over the hot mop. The hot mop goes up 12 inches and everything is down to studs. I planned on using cement board to cover all the walls but I know i'm not suppose to screw the cement board directly into the hot mop section.

Do I have the cement board over lap the hot mop by 2 inches then float up the wall with thin set?

Or

Do I have the cement board go all the way down to the mortar bed and use cement behind it to adhere to the hot mop?

Second question since the hot mop goes over the shower curb. I planned on putting Cement board over that as well. Would that be okay to screw into?
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Old 07-09-2018, 08:27 PM   #2
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Welcome, Justin.

I've separated your post from the other visitor's six year old thread to avoid confusion on both projects.

Best bet would have been for you to install your CBU on the walls prior to placing your final mud bed on the shower floor so you could use the mud bed to anchor the bottom of the CBU wall panels. You could still carefully remove your existing mud bed and do that. Deck mud is dirt cheap and DIY labor's free, eh?

In the alternative you could simply stop the bottom of your wallboard just above the existing mud bed and hope to anchor the bottom when you set the floor tiles. I don't care much for that plan, but that's the way it's done when using a fiber/cement board on the walls instead of a CBU.

You absolutely cannot install any kind of CBU at all on your curb. The only acceptable method of treating such curbs is to bend some metal lath over the curb and shape the final curb with wall mud, sometimes called fat mud. If you'll visit our Liberry and find the Shower Construction section you'll find one or more articles in there showing just how to do that.

We can guess that you're in California, but it'll help with some kinds of questions if you'll add a geographic location to your User Profile so it appears in each post.

My opinion; worth price charged.
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Old 07-09-2018, 08:34 PM   #3
ZZZK
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Code states no penetrations lower than 1" above the FINISHED curb height. Key word FINISHED height meaning above final tile.

For the wall cement board that means the lowest bottom screw will be 1" above FINISHED curb. Use some thinset at the bottom of the cbu below the screws to space and fill voids. You can screw through the hot mop ad long as you obey above rule. Predrill the hole to avoid cracking the hot mop. Space the board 1/4 above the floor of the hotmop.

A cement board curb cannot be fastened without violating above rule so the curb must be made with lath and fat mud. No other way to do it. Do not attempt to do it with cement board. Do not fasten the lath on the inside as it will violate above rule.
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Old 07-12-2018, 11:03 PM   #4
Justinfive10
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Thanks for the advice. Sorry I may have created a duplicate thread on the same topic.

I'm in California and I'm realizing that hot mops are not as popular as i thought. It's hard to find information on it or even youtube videos.

I do not necessarily need to apply cement board to the shower dam. I just thought it might look nicer with a thicker boarder. Since it's code to not apply Cement board to the dam, I'll just tile over the hot mopped section.

What do you think of having the cement board come down to the mortar bed but using liquid nails to hold it in its place. Since the hot mop goes up only 10 inches I can screw the cement board at the 10 inch line.

Once this is all done I plan on taping my joints and using red guard to cover the whole thing.
I've heard using plastic or tar paper behind studs was good to do, but I also heard you shouldn't use plastic and red guard both because it creates a moisture sandwich. Is that true? I think I should be good with just red guard anyways but i didn't think that the extra precaution would actually cause more harm than good. The bathroom is in a basement so I thought the extra precaution would be better.
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Old 07-12-2018, 11:11 PM   #5
ZZZK
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Justin you can't tile the hot mop directly. The curb needs to be formed using lath and fat mud with no penetrations on the inside or top of the curb for the lath.
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