Hey Guys, Im re-tiling the area behind the bar in a resturant. It's a 6x6 quarry tile on a wood subfloor. The existing tile has water under it and is leaking to the dining room below. There does not appear to be any backer board or anything over the plywood, and a lot of the grout has cracked out allowing the water to penetrate.My question is, What kind of liner or moisture barrier should I use, and I'm assuming that the grout is cracked out because there is no backer board under the tile. What would you guys do?

Hi Carpet man

It's hard to build a moisture barrier unless there is substantial material (and wood isn't an option) between the barrier and tile.
I would suggest building a mortar bed and waterproof the bed with Laticrete 9235 before installing the tile. It sounds like you have a continuous moisture problem so I would be inclined to keep as much moisture from soaking into anything past the tile.

Tell us a bit more about the area and condition as well as amounts of moisture that will occure etc so that we can steer you right.

This area is subject to a lot or water, washing dishes, slinging tequila around, and who knows what else. There are 4 drains in the floor with not really any slope to them. I was looking at the Ditra system , but am unfamiliar with it. Best I can tell, you would roll that stuff out over thin-set and seal it together using Kerdi-band. And then set the tile on top.?? Would I need backer board under the Ditra? What about at the drains? They are like little sink basins that are in the floor that you tile up to. Not sure how to seal that up.

If I was to build a mortar bed, what mortar would I use? The guys at Home Depot told me that tile mortar and brick mortar are the same, but another tile man told me that brick mortar would shrink and crack.?? Any info would be very much appreciated.!!

CM, a mortar bed is made from about 5 parts masonry sand and 1 part portland cement. You could install it with an almost un-noticable slope to the drains. It would be very easy to apply a liquid membrane to afterwards for waterproofing.

There are special drains made by Schluter which work with a waterproof membrane (Kerdi) to ensure complete waterproofing of the floor but it might not work with your drainage system. Check it out anyway at Schluter Waterproof Membranes and Drains

As for Ditra, maybe Bri has more input about how it would work for this application. I don't think it will work as a "run-off" system because of all the little pockets which will hold moisture but we'll see what Bri has to say.