Cement board in shower renovation

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Elizaf

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Help! I've torn down my old shower and had a professional install a new cement shower pan with liner. I'm ready to put hardie board on walls and then apply Redgard and then tile. Please tell me how much space I leave between the first wall board of hardie board and the floor. Also, what needs to be done to seal the bottom piece of hardie board near the floor?
Any helpful hints appreciated!
 

Jadnashua

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There are two 'classes' of cement board, and HardieBacker is in the class called fiber cement boards. That type CANNOT be embedded in the shower pan, which poses its own problems in fastening the bottom since there can not be any fasteners within 2" above the top of the curb, so that leaves the bottom section flapping in the breeze!

Second big thing...is the liner flat on the floor, or was a preslope installed first? The later is the only way approved by plumbing codes (the liner is the waterproofing layer in the pan, and code calls for that to be sloped to the drain which it can't be if flat on the floor!).

But, assuming everything else was done right: dam corners on the curb, NO fasteners through the liner anywhere inside, on the top, and ONLY low on the outside except no lower than 2" above the curb, AND they did a flood test to verify that the liner was intact...it should work.

Hassle is that one study indicated that 70-80% of the tiled showers built in the USA are not done to industry standards...that's pretty sad, but true!

The HardieBacker should terminate at least 1/4" above the top of the setting bed - that's not the liner, that's the mudbed on top of the liner. If the HardieBacker has a vapor barrier behind it (plastic sheet or roofing felt), you don't need to do anything to the bottom edge.

James Hardie has instructions on their website, and you can get the industry guidelines at www.tcna.org. The latter is the industry bible, but product specs give sometimes more specific instructions.

I suggest you check out www.johnbridge.com for help in building a shower that will last without issues.
 

Elizaf

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The shower pan was presloped prior to the thick plastic liner being put down. Then the top layer. However I've noticed it doesn't appear to slope very much from walls to drain. How much slope should the mortar bed have when level is paced on it?
My hardieboard will not have a vapor barrier behind it. It will be treated with Redgard. I understand leaving 1/4 gap at cement board bottom. But does the Redgard also just stop at the base of the bottom board. I'm just trying to figure out how to make sure water doesn't get through the tile and possible leak.
 

Jadnashua

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The preslope should be a minimum of 1/4"/foot...the setting bed on top of it should be parallel to the preslope, so should match that slope exactly. Tile is NOT the waterproof layer...the liner is. There WILL be moisture that gets beneath the tile, and if the mudbed is done properly, with the preslope beneath it and the weep holes open in the drain, it will not accumulate, and just weep out into the drain.

If you want a surface applied membrane, then it should be tied to a surface applied layer in the pan, which must then be bonded properly to the drain, or there will be moisture that is trapped between the surface and the liner...not a great idea. IMHO, liquid applied membranes are not the best solution.
 
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