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Orientation question about cement board on a step


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06-16-16, 05:24 AM   #1  
Orientation question about cement board on a step

I've got a step and platform that goes down to a concrete floor. I'm laying tile over both. For the step, I'm first applying thinset and cement board. My question is how to best lay the cement board on the exterior angle of the step. See image. Blue is cement board. Thinset not shown. My guess is A would ultimately give me more support when someone steps down the the edge.

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Typically, I'd use more thinset and cement board tape to tape the seams. Do I still do this for right angles? Just leave the gap?

Once the cement board is in place I plan to use a rondec-step which is just a metal piece to protect the edge:

Schluter Rondec Satin Nickel Anodized Aluminum 3/8 in. x 8 ft. 2-1/2 in. Metal Bullnose Tile Edging Trim-RO100AT - The Home Depot

I've never used these before. I was going to get one that had a right angle such that it would go underneath the tile on the vertical surface as well as the horizontal, but it doesn't look like they make them that way to go UNDER the tile. I'd rather see tile on the vertical edge than a metal lip.

Anyway, I assume you screw these down with cement board screws prior to tiling and so I wasn't sure if using these rondec-step pieces would influence the decision on what orientation to use.

Thanks for the help!

 
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06-16-16, 06:28 AM   #2  
Go with A. I've never seen tape used on steps ..... but I'm a painter, not a tile guy.


retired painter/contractor avid DIYer

 
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06-16-16, 02:44 PM   #3  
marksr,

I agree, but I'm hoping for a "tile guy" answer. I should mention the cement board is only 1/4" thick. Whatever the orientation, and even if I don't use the tape, I'm wondering if I should fill that 1/8" gap with anything.

 
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06-22-16, 05:18 PM   #4  
I know on perpendicular surfaces with grout you're supposed to use caulking, not actual grout, but for gaps like this that are under the tile I was less sure. I ended up going with method "A" above although that 1/8" still bothers me as it's potentially a break point every time someone puts downward pressure on the edge of the tile. Also, I never found any other Rondec solution so I went with the flat bar. I didn't see any point in using mesh tape on a right angle surface.

 
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06-23-16, 03:56 AM   #5  
Door #1 with overlap on top. Use alkaline resistant mesh tape and embed it with thinset. For the Rondec edging, make sure you do the vertical tile first, then embed the metal in thinset on top. Don't nail it as you may hit it too hard and bend it. Then lay your tile with a normal layer of thinset. Any time you change planes, you should use a sanded grout caulk since it will expand and contract. Grout will just crack.

 
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06-23-16, 02:25 PM   #6  
Thanks for the reply. I couldn't wait so I already laid the cement board, but not the tile. Looks like I guessed right. Other than the thinset, everything else you describe sounds right to me and it's what I've done on other tile projects.

Regarding the 1/8" gap (as shown in illustration A), that's the one I would fill with thinset and cover with mesh tape? By applying thinset to only half the tape at a time, I could bend it over into a right angle over teh vertical and horizontal surface. It's only 1/4" cement board, so I don't imagine it will grab much on the edge of the BB.

Although this gap will be underneath the tile, my concern is the same as you describe for the grout later on when tiling. Because it's a right angle intersection, won't this 1/8" packed with thinset be just as likely to crack as grout? On the other hand, even if I could do it cleanly, putting caulk under the tile to fill the 1/8" gap doesn't seem right either.

Perhaps I should leave the 1/8" gap in the cement board as it is, empty. Then, when I tile, leave another 1/8" gap between the vertical tile and the bottom of the Rondec creating a deeper gap which I would then fill entirely with caulking? (Gap depth would = 1/8" between backerboard, thickness of thinset once set, and thickness of tile). Not as strong as cement, but unlikely to crack from expansion.

Maybe I'm just overthinking this too much. lol.

 
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06-23-16, 02:53 PM   #7  
You are overthinking it. IF you are worried about that gap, paint it with RedGard, and call it a day.

 
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06-23-16, 05:22 PM   #8  
I'm using Reguard for a few hairline cracks, so I already have some on hand. Using it for the 1/8" gap is a great idea! It offers flexibility closer to caulk and it's made for going under the tiles. I don't imagine it goes on very thick, but it's worth a shot. Good idea.


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06-24-16, 05:53 AM   #9  
Or not...

"Do not use to bridge or cover over existing expansion, control,
construction, cold or saw cut joints; use Crack Buster® Pro Membrane
for control, cold or saw cut joints."

"Do not bridge joints designed to experience movement. "

http://www.custombuildingproducts.com/tds/tds-104.pdf

 
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06-24-16, 07:46 AM   #10  
Stuff it with thinset and mesh tape over it. You don't fill gaps with brush on crack isolation membranes. If this is a wet area such as a shower, yes, paint over the mesh tape with redgard.

 
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06-24-16, 02:04 PM   #11  
As I understand it, the idea is that a perpendicular intersection will expand differently and cause a crack, which is why you use caulk, not grout when finishing tile work. Seems to me the same concerns should be valid below the tile with regard to the perpendicular cement board intersection. BUT, having not better solution anyway, I'll defer to your judgement and use the thinset and mesh tape as I would on a horizontal joining of cement board. This was Chandler's first recommendation as well. Thanks for the help and for hearing me out.

 
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06-24-16, 03:36 PM   #12  
Who cares what goes on underneath the tiles, the only cracks you are concerned with are on the visible surface which you control with flexible caulking not grout. Hope that better explains.

 
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06-24-16, 04:57 PM   #13  
Ah, okay, so there's no concern the thinset will push up on the cement board causing a hump or anything like that and it's understood that eventually it will crack but not be seen thus absorbing the expansion. This just adds to the understanding why "A" is better than "B" because the grout line is on top of the cement board thinset line.

 
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