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Unread 01-25-2019, 12:57 AM   #46
mrberryman
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I used thinset under the Wonderboard I used in my bathroom and it's been fine. I used a Mapei Rapid Set. I wet the OSB down a bunch with a sponge and mixed it pretty runny under the cement boards and it's been fine. Also the stuff sticks extremely well to the wetted down OSB, I found it harder to scrape off some excess off the wetted OSB compared to even the Wonderboard.
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Unread 01-25-2019, 09:34 AM   #47
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David, the thinset mortar under the CBU panels for a floor installation is not there to bond the panel to the subfloor, it's there to fill any voids and provide a 100 percent footprint for the CBU. The mortar holds it up, the mechanical fasteners hold it down.

The thinset mortar manufacturers, as a rule, don't want you to try to bond anything to OSB with their products.

My opinion; worth price charged.
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Unread 02-02-2019, 06:02 AM   #48
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Thank you both!
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Unread 02-02-2019, 06:08 AM   #49
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With the hardi board I have on my walls, the manufacture recommended the hardi boat be a 1/4 inch above the shower pan. They then recommended to caulk with 100% silicone underneath it to seal it up. My question is, does there need to be anything else placed over the seam transition from the pan to the wall? Does it need to be mortared and have the alkaline resistent tape embedded into it like at the seams? Or does it stay as it is and the tile get placed over it?

Thanks.
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Unread 02-02-2019, 09:23 AM   #50
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Quote:
Originally Posted by David
...the manufacture recommended the hardi boat be a 1/4 inch above the shower pan.
That's a typo?

Have you already placed your final mud bed, David?

Do you still plan to use a waterproofing membrane over your walls?

[Edit] I also brought your OSB question here from that very old thread for continuity. Best to keep all your project questions on this thread so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one.
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Unread 02-04-2019, 06:10 AM   #51
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Sorry, yes it was a typo. “The hardi backer board.” It’s the Hardie 500.

Before I got on this forum I was going to put the waterproofing membrane on the walls, curb and shower pan. Since then I’ve been up in the air about whether or not to do it.
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Unread 02-04-2019, 11:15 AM   #52
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Quote:
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Have you already placed your final mud bed, David?
Did you use a moisture barrier behind your wallboards?
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Unread 02-04-2019, 02:31 PM   #53
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I put tar paper behind them.
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Unread 02-07-2019, 03:00 PM   #54
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Another question for you all, but separate from my shower. So i'm doing a full remodel on my entire house that i'm not living in. I'm currently adding 1\2" plywood underlayment to all bedrooms before new carpet goes in them. Doing so will bring the carpet up to about level with the floated hardwood floors that are going down in the living room, dinning room, kitchen, and hallway. The floated hardwoods will also have 1/2" underlaymet under them as that's what the manufacturer recommends. My sub floor in the house is 3/4" OSB. In the two bathrooms and one laundry room will be tiled floors. The bathrooms with have 12"x24" porcelain tile. The smaller bathroom floor is about 5'X 8'. The bigger bathroom is an odd shape but its about 11' X 4'. the laundry room will have 8x8 ceramic tile. The laundry room is 7'x7'.

My plan was to put 1/2" Hardibacker board on the tiled floors to make them approximately the same height as the hardwood and carpet. After reading my concern is that I am going about the floors the best way. My floors are not completely flat, it looks like there are some 1/4" valleys, so I know I will have to work on that.

Ive been seeing on forums that people are recommending putting down 1/2" underlayment over 3/4" OSB, THEN putting down 1/4" hardibacker board. obviously if I do that, My floors will be an 1/4" taller than originally planned for.

I know I havn't gotten to my question yet.

Should my floors be sufficient with simply the 1/2'' Hardibacker board as originally planned or should I go back to the drawing board? Also, I know it's best start with a flat substrate, As far as the 1/4" valleys that I'm looking at(after I've already been sanding the floors highspots), would it be acceptable to put the Hardibacker board down with the floor as is then use a self leveler over the Hardibacker board?

Second question. The underlaryment I've put down for the bedrooms that will have carpet in them. The underlayment panels have a 1/16 to 1/8 gap between them for spacing. Should those gaps be filled with some sort of self leveler to fill them or will they be fine as is? The floor will have a thick carpet pad then thick carpet.

Thanks for the replies in advance!

Since I've written this I've been reading about Ditra. Also, what are the thoughts on it vs. the cement board? Does the floor have to be perfectly flat for the Ditra to work correctly and there to be no lippage?
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Unread 02-07-2019, 03:25 PM   #55
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how did you fasten the tar paper and did you treat the fastener penetrations and seams with anything?
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Unread 02-07-2019, 03:52 PM   #56
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The tar paper seams overlapped on a stud and was stapled to the studs. The seams would have then been sandwiched by the pressure of the cement board being fastened. As far as anything on the screw holes they were covered with mortar.
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Unread 02-07-2019, 04:33 PM   #57
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I wouldn't worry about the staples thru the tar paper on a vertical surface.

The surface for Ditra will need to be flat also. You can get a flat floor with a mud job or SLC. Everything else will follow your wavy floor if you don't get it flat first.
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Unread 02-07-2019, 04:39 PM   #58
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1. There is no need to use two layers of cement board. Whichever one gets your floor to the desired height is the one you want.

Yes, always level on top of the cement board.

2. Those gaps are necessary for expansion and contraction. Leave them alone.
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Unread 02-07-2019, 05:03 PM   #59
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Davy, When you say mud job, do you mean spot filling the low spots with motar and letting it set up? As far as the other thing that you mentioned. Is that a self leveler that can be applied to OSB? I'm not faimiliar with it.

Kman, Thanks for the reply.
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Unread 02-07-2019, 05:52 PM   #60
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David, the "mud job" Davy is talking about is the use of deck mud similar to what you used to form your shower floor, but making a flat, and level if desired, substrate for your tile installation. I would use a 5:1 sand to Portland mix instead of that 4:1 pre-bagged mix you used, though. Absolute minimum thickness of 3/4" over a cleavage and expanded metal lath or the better choice would be a minimum of 1 1/4" mud with welded wire mesh in the vertical center.

Yes, the SLC he recommended is a self-leveling compound. You'll need to refer to the specific manufacturer's recommendations as to how it might be installed over your OSB subfloor.

My opinion; worth price charged.
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