I am building an interior hearth and surround that will ultimately be covered in cultured stone for a woodstove. I have constructed the hearth of 2X6 covered with 1/2" plywood with wonderboard over that. I have questions about securing the wonderboard to the wall for the surround:
-Is it necessary to secure 1/2" plywood to the drywall and then attach the wonderboard to the plywood? I am concerned that simply screwing the wonderboard to the studs will not provide enough support for the stone.
-Is it necessary to use a vapor barrier when installing wonderboard for an interior installation?
Last year I finished a similar project and am also a newbie so maybe my experience will be applicable. In my case, I built in a NG fireplace and used natural stone veneer (heavier than cultured stone). I used 2x4 and 2x6 framing with clearances per the fireplace manufacturer. I attached 1/2" Durock cement board directly to the framing using 1 5/8" screws designed for use with Durock cement board ( I forget their trade name but you'll find them near the Durock sheets). I used polymer modified thin set mortar on all board seams and then to adhere the stone veneers to the cement board. All work was inspected and approved in St Paul, MN and has been working great. The natural stone veneer and installation instructions can be found at http://www.nsvi.com/.