# Cement board prep for tile



## gowings (Nov 10, 2013)

Does anyone have a video link or FYI list for cement board prepping for tile. I've installed the cement board on the walls and tile niches. I siliconed the joints of the cement board in the niches. So whats next. I've seen some videos but seems the steps are not similar and parts are not explained why they did certain things or not. I can't seem to find anything on the niche application and cement board.

Do I just mesh tape the joints with thin set. What do I do about the inside corners of the niche's. I use hydroban quite a bit but usually only applied on diamond board for prep before tiling.

Whats the purpose of the mesh tape. I'm curious

Why not just hydroban the joints and corners. 

Do I do anything with the open faces of the tile niche edges on the 90's.

Thanks for the help


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## charimon (Nov 24, 2008)

watch Sal
he has a great you tube channel, and a couple hours wathcing him will be of great help.
https://www.youtube.com/user/saldibs

I am not trying to be cheesy or corny but Sal is a fellow Tile Geek who has a gift for video.
https://www.youtube.com/watch?v=j6C1Djy0ZE8


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## gowings (Nov 10, 2013)

Thanks I've watched Sal. But no info on tile niche prep with cement board. At least I didn't see anything on the subject.


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## Robinsonfam1 (Feb 17, 2011)

i would dig out the silicone as much as you can. then mesh tape and thin set all corners inside and out. then hydro ban. 
be sure to use alkalai resistant mesh tape made for concrete board, not drywall mesh.

the purpose of the mesh is to create a bond between the boards for one continuous plane. creates a stronger and more sealed enclosure.

yes i would waterproof the whole shower. water will still wick through the grout. it will be much better and longer lasting job.

ive never used hydro ban so i cant comment too much on it. i'm more mapei and red-gard user based on availability around me.

same with the diamond board you are referring to....if it is certainteed diamond back then go to their website and you will find a complete installation guide.


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## CO762 (Feb 22, 2010)

gowings said:


> Thanks I've watched Sal. But no info on tile niche prep with cement board. At least I didn't see anything on the subject.


Long time ago I saw an article in fine home building where some chick was stuffing ice and water shield into a niche. She was working pretty hard at it, so she had great determination in protecting that niche from water penetration.


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## gowings (Nov 10, 2013)

Robinsonfam1 said:


> i would dig out the silicone as much as you can. then mesh tape and thin set all corners inside and out. then hydro ban.
> be sure to use alkalai resistant mesh tape made for concrete board, not drywall mesh.
> 
> The silicone was beaded on the plywood joints before the cement board was installed over top.


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## avenge (Sep 25, 2008)

gowings said:


> [QUOTEThe silicone was beaded on the plywood joints before the cement board was installed over top.


Guess it doesn't hurt but you want to seal the cement board from water penetration before it can get behind it not after. And why plywood?


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## AGullion (Apr 19, 2015)

First rule on cement board is avoid it. You really can't seal the lower edges, and water will wick up into it . Topical membranes can hold water in or out , so be careful .


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## AGullion (Apr 19, 2015)

This is not going to go over very well, but topical membranes , no matter how good they are, don't belong in a traditionally constructed shower. It's not designed for it . if you can get it , use a non porous tile board instead


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## CarpenterSFO (Dec 12, 2012)

Tape and thinset every seam and joint, then cover with membrane - either sheet (Kerdi) or liquid (Hydroban). The purpose of the tape is to provide strength and stiffness and to make a stable scaffold to tool a surface at the joints - flat and 90s, inside and out - for adhering your membrane.

I've never heard of silicone on the CB or ply, but it shouldn't be a problem - it will be hidden behind the membrane anyway.

Why not just hydroban the corners? Hydroban is a membrane, not a gap filler, and it won't add any strength to the joints.

Mesh and thinset every seam and corner, then membrane, per manufacturer's instructions.


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## CarpenterSFO (Dec 12, 2012)

AGullion said:


> This is not going to go over very well, but topical membranes , no matter how good they are, don't belong in a traditionally constructed shower. It's not designed for it . if you can get it , use a non porous tile board instead


What do you mean by "topical" membrane?


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## AGullion (Apr 19, 2015)

Anything you put over the board , at some point has to stop. The same weep holes that let water out, let water in . it looks impressive to use those products, but water will get behind it from the pan system . it's the biggest misconception in wet area tile work today


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## AGullion (Apr 19, 2015)

You can do it with a schluter drain, but you better not have a pin hole .


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## gowings (Nov 10, 2013)

CarpenterSFO said:


> Tape and thinset every seam and joint, then cover with membrane - either sheet (Kerdi) or liquid (Hydroban). The purpose of the tape is to provide strength and stiffness and to make a stable scaffold to tool a surface at the joints - flat and 90s, inside and out - for adhering your membrane.
> 
> I've never heard of silicone on the CB or ply, but it shouldn't be a problem - it will be hidden behind the membrane anyway.
> 
> ...


Bob
I have the alkaline tape is it hard to do the corners. I've used drywall mesh and its not the greatest for 90's for taping, So I'm sure it creates the same issues getting a good crease to apply it.
Also the silicone was applied to the plywood box corner seams. Then the cement board(pain in the ass, I've learnt my lesson on its dust and cutting negatives, it's back to wedi or diamondback) applied over top
Thanks


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## CarpenterSFO (Dec 12, 2012)

gowings said:


> Bob
> I have the alkaline tape is it hard to do the corners. I've used drywall mesh and its not the greatest for 90's for taping, So I'm sure it creates the same issues getting a good crease to apply it.
> Thanks


You have to be careful with the corners, no doubt. You are trying to be neat, and to apply enough thinset to do the job without making excessive buildup.


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## CarpenterSFO (Dec 12, 2012)

AGullion said:


> You can do it with a schluter drain, but you better not have a pin hole .


Yes, indeed. Now, the restriction is really that you better not have a pin hole anywhere that moisture will accumulate.


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## AGullion (Apr 19, 2015)

Well said


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## jaydee (Mar 20, 2014)

I'm a fan of kerdi, the have specific pieces for corners, then a liquid membrane also.
Better do it right ONCE then to have to start over..


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## AGullion (Apr 19, 2015)

This thing of mix n match is nuts.....even some manufacturers are confused.


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## charimon (Nov 24, 2008)

AGullion said:


> You can do it with a schluter drain, but you better not have a pin hole .


There are other methods out there besides Schluter drains on a mud bed ( which I like to use) but here is not the place to discuss them as they are hybrid systems which are not backed by any manufacturer but are in my opinion better than any single source system available.


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