Q:

My builder tells me that “green-board” drywall is the proper backing for a tile shower, but I believe that cement board is better. What do you think?

Steve Jordan, via email, None

A:

Tom Meehan, a master tilesetter and the owner of Cape Cod Tileworks in Harwich, Massachusetts, replies: Steve, by all means, stand your ground. Green board is not the proper backer for a shower stall unless a complete waterproof-membrane system is applied over it. Even then, I still believe that cement board is the proper substrate to use.

In the early 1970s, I was one of many tilesetters who used green board. We thought it was waterproof drywall because it has a wax coating over the paper facing. The reality, though, is that green board is moisture resistant, not waterproof. It’s not moldproof, either. When moisture gets behind the tile, the paper facing on green board becomes mold food. The waxy coating is like a mold appetizer.

In the late ’70s, cement board came into the picture and has proved to be a superior product. It is a bit more work to cut and install, but when tile is installed over it with thinset cement, the system does not fail. As a test, I once installed a couple of pieces of tile on a small piece of cement board, then dropped it into a pond behind my house. After two months, I couldn’t separate the tile from the board.