Greetings, I am not sure if this s/b in this section or in plumbing, so I will post it in both.

We are adding a whirlpool tub to our bathroom addition and it requires a tub deck.

The exterior walls are all framed and insulated (Icynene).

Should I rock the walls first and then build the support deck on top of the drywall? (Hopefully this is the right way as the wall is already rocked).

OR

Should I cut out the rock to attach the framing members directly to the studs?

Should I have used cement board instead of drywall? (The drywall is DensArmor Plus if that makes a difference)

Now for the shower enclosure. I am forced to use a mudbed as I can't move the existing drain. So...

For the walls, should I use an EPDM membrane behind the cement board (hardie board)? I have found a good link for how to build the mudbed for the shower pan which will use an EPDM membrane.

As always, thanks for your help.

Dan

You can attach the framing members against the rock. Use 3" screws. Dont forget an access door for the pump & electricals on the side of the framing deck. Depending what kind of tub, they usually rest also on the floor and not just suspended by the tub deck. You dont need cement board on the walls around the tub. Your walls shouldnt be getting wet sitting in the tub.
As for the shower, you dont need EPDM up the whole walls, just up the 3" up from the shower curb, 6" above floor in showers w/o curbs. Make sure you seal the Hardiboard joints & corners w/ fiberglass mesh tape and thinset compound you'll use to set the tile. If the joints are extremely tight, you can use flexible caulking @ the joints. The Tile Council web site is www.tileusa.com