[costgeek]

Hello again all. After practicing on the small bathroom I'm finally doing the master. I feel like I know what I'm doing for the most part, but do have a few questions.

The shower will be 4'x6', and I'm doing a mortar pan, with a topical membrane and a linear flange drain at the wall. Right now the entire bathroom has a 1/2" subfloor with some thick cement board on top (it looks 3/4"). All the cement board will come out and be replaced with backer board.

The last time I did a mortar pan it had a center hole drain and sat on top a 3/4" subfloor. This new situation raises a couple questions for me:

1) I don't feel like 1/2" plywood is enough to set the pan on. Should I reinforce it with more plywood, or can I just use backboard along with the rest of the bathroom floor? Does it need to sit on wood so it can shift or will the backboard keep it from cracking?

2) Following the drain instructions for a topical membrane installation, the 3/4" thick drain sits on the subfloor. This makes my pan 3/4" thick at the drain. I usually feel comfortable following manufacturers instructions, but that's a lot thinner than the 1-1/4" minimum you get with a center hole drain. Am I okay, or should I slide a 1/2" board under the drain to make the pan thickness 1-1/4"?

Thanks!
CG

 

[oh'mike]

1/2" ply is to thin ,in my opinion, so add another 1/2" on top---or cut out the old and add 3/4" BC--

3/4" mud bed (at its thinnest point) will be fine---------

Backer board has no structural strength--so do not place that under the mud bed----nothing to be gained by doing that except extra time and expense.

 

[costgeek]

Perfect. Thanks OM.

 

[JazMan]

Hi CG,

½" subfloor is very unusual, how old is the house? They may have used ½" if the rest of the house is hardwood. But I would bet it's really thicker than ½".

Right now the entire bathroom has a 1/2" subfloor with some thick cement board on top (it looks 3/4").

That thick cement board is NOT a board. It must be a mud job.

1. Do as Mike said to the subfloor, the entire area.

2. I agree ¾" deck mud is good if the subfloor is sturdy. You can shim the drain if you want to. I don't see where you get 1 ¼" thick mud with a regular drain, it ends up as thick as you make it. Hopefully over 1" cuz being it's in the center you are bound to stand over it where you will not stand on a linear drain, less stress.

Can you tell us which method and which surface membrane you will be using? Are you using lath? More details if you can.

Jaz

 

[costgeek]

You're right Jaz. I guess it is 19/32". All the demo is gone, but I swear some of what I tore out was thinner. Anyhoo...should I still beef it up 1/2" given that my pan will only be 3/4" at the drain?

Yep you're right...it's mud. Didn't pick up on that before.


The last centerset drain I did also had a topical membrane. The Laticrete flange drain minimum height is 1-1/4". I just thought it was odd that a linear drain only requires 3/4". In theory you could still install the drain in places where you would step on it.

So this is what I'm doing:

Lay some yard fabric on the subfloor, then lath on that. Lay down some sand mix in the drain area then jam the flange drain into it and level. Finish filling under the flange then lay the rest of the pan with slope on top of the lath. After everything sets up I'll paint on two coats of Hydro Ban with fabric at all the joints/seams. I'll cover everything at the floor +12". I'll do the seams and joints all the way to the ceiling as well as recessed shelves, the curb etc. The Hydro ban will paint all the way onto the drain flange, then the tile will stop right at the edge of the trough.

See any potential issues?

 

[JazMan]

Why yard fabric? They'll let moisture go through, wrong material for this job.

I'd go higher up the walls too.

Jaz