Drywall behind concrete board

[DAVID MACFARLANE]

I am remodeling a bath that is a bit too wide for an alcove tub. The original builders got around this by layering two pieces of drywall (not green--built in 1985) so the top layer hung over the tub flange. Actually, all three walls around the old tub were just drywall. To make up for the gap on one end, I was going to put a layer of green drywall, concrete board over that, green waterproofing goop over that, and then tile. I am going to be okay with that green board on one wall tucked behind the concrete board? Thanks.

 

[Jadnashua]

It can get messy with the cement board (cbu) sandwiched between a waterproof coating and a nearly waterproof one behind...generally, you don't want to do that...one on top of the tiling surface, or one behind it...that's to protect the structure.

To save a bunch of work and materials, I'd just cut some strips of either ply or solid wood and use them as spacers rather than putting multiple layers of stuff behind the cbu.

And, if I were wanting to waterproof the tub surround, I'd probably use something like WediBoard, or KerdiBoard, that is both waterproof and a good tile backer and do it in one step rather than multiple layers.

Check out some of the videos over at www.schluter.com on doing a tub surround to get an idea of what I'm talking about, then check out www.johnbridge.com for help in doing it right. Lots more tiling pros over there.