Water barrier

[Tom Rees]

What is code for a moisture barrier in showers and steam rooms. A tile guy I know puts tile directly over green board or durarock with no barrier, what is required. I know what is right, but what is required?

[Jerry Peck - Codeman]

Hi Tom,

I know what is right, but what is required?

First, a question: What is "right"?

Second, green board or MR board (i.e., moisture resistant board) IS NOT ALLOWED to be installed in the locations you mentioned it being installed. That alone would make those tile people totally wrong.

Let's take Durock (Wonder Board, etc., several different brand names for a similar product). That board IS allowed in the areas you mentioned. No water barrier is required or needed over them, and installing a water barrier over these boards would defeat the purpose of the boards and case the tile to have nothing to bond to. There is also no need to install a water barrier behind these boards as these boards are designed to become wetted with the water which soaks through the grout between the tiles, then these boards dry out. Installing a water barrier behind them would only slow the drying out process as now the boards would only be exposed to air on one side, and limited to the small area of the grout lines.

Installing a water barrier behind green board is simply going to turn mush (what green boards become when they get wet behind the tile) into gypsum chowder (which is nothing like clam chowder - which I dislike too).

The only place green board is allowed as a tile backer board is in DRY AREAS, i.e., NOT around tubs, NOT around showers, and definitely NOT in steam showers.

Which takes us back to:

I know what is right,

First, a question: What is "right"?