Basement Bathroom Tile Question [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Basement Bathroom Tile Question

02-03-2013, 11:57 AM
We are in the process of renovating our basement which we are doing in two phases. First was the living area, second is the laundry/bathroom.

Phase 1 is complete but that contractor is not coming back. Long story!

Now we are starting Phase 2 with a new contractor. Installation of all rough-in's (including drain lines in the floor) for the laundry room and 3-piece bathroom (sink, toilet, tiled shower).

The concrete slab wicks moisture through hydrostatic pressue. Confirmed this through hydrostatic tests and the appearance of efflorescence. MANY days spent reseraching this. Long story short, the solution for the hydrostatic pressure is to use a capillary break like Delta-FL membrane. This is confirmed as the best defence through building science engineers short of redoing the slab and weeping tile. Plywood subfloor was installed over Delta-FL and laminate as the finish surface. Works great, no musty smell in the living area, warm floors even when outside temperature is -18C.

So now that we are doing the "wet" rooms, the finish surface will be tile. After the concrete is broken up, the rough-ins are installed, and the slab is repoured, my contractor wants to dry-pak the floor to bring it up to level, then use Ditra for the isolation membrane, and then tile.

My first thought was to put Delta-FL on the concrete after the rough-in's were done, then plywood, then ditra, then modified thinset, then the tile. PHEW!

I am starting to think that this is overkill, as the Ditra should act as a capillary break. Also, thinking about further, the area between the Delta-FL and the Ditra would make a double water barrier which would trap any moisture and prevent it fom dissipating, NOT GOOD.

So I guess I'm looking to people on this forum to confirm the Dry-Pak on the Concrete followed by Ditra and Modified Thinset method. Anything glaringly wrong with this?


Derek Jenkins

Sponsored Links

02-03-2013, 02:46 PM
Welcome, Derek. :)

Let's start by clearing up some terminology. You indicate you have a hydrostatic moisture problem. If that's the case, you're not gonna find a tiling substrate product that will be warranted by the manufacturer for your application. Moisture vapor emissions, yes; negative hydrostatic pressure, no.

I don't think your Delta-FL is designed to deal with hydrostatic pressure, either, and I see no indication that it's been tested for use under ceramic tiles at all.

The principle they're relying upon for containment of moisture vapor emissions is exactly the same as for Schluter's Ditra. And Ditra is specifically designed for ceramic or stone tile applications.

I would absolutely not install plywood over a concrete slab, especially a below grade slab, that is to be tiled. Using deck mud to flatten (and level if desired) the floor and using Ditra on that for your tiling substrate would be a good choice so long as you're dealing with a quantifiable amount of moisture vapor emissions and not negative hydrostatic moisture issues.then ditra, then modified thinset, then the tile. If you'll read the Schluter instructions for Ditra you'll also find that you want to use an un-modified thinset mortar to set your tiles over the product.

My opinion; worth price charged.

02-03-2013, 02:46 PM
Welcome Derek. :)

After the concrete is broken up, the rough-ins are installed, and the slab is repoured, my contractor wants to dry-pak the floor to bring it up to level, then use Ditra for the isolation membrane, and then tile.

This done properly is a well constructed floor and sounds like all you need. My vote is typically against putting of any kind wood over a concrete slab, especially one with moisture issues.

What level of moisture do you have coming up though the slab? Lots or just a little? :)

02-04-2013, 10:54 AM
Thanks for the comment. As to the moisture amount, the only time you see any moisture is when you cover an area for a week or so and then remove it you will see that the concrete is damp. Maybe vapor pressure is the better term versus hydrostatic pressure.