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Tiling and Waterproofing a Ceramic Tile Balcony with "Ditra" from Schluter Systems

September, 2005

John P. Bridge

Tiling exterior balconies and other elevated outdoor living areas has always been difficult, not so much in the tiling aspect but in waterproofing under the tile installation. Methods of waterproofing have been for the most part feeble inasmuch as success has depended upon the use of roofing materials which were not particularly suited to ceramic tile and stone applications. Results have been unpredictable to say the least.  I'm guessing the average (waterproof) life span of a traditionally tiled balcony is less than twenty years, and this would be in the best of circumstances -- not long at all when you consider that other tile applications can easily last the life of the building.

You start with a conventionally framed flat roof deck which may or may not be sloped away from the main structure.  Add to that a hot mopped tar roof (or another roofing type membrane) to complete the waterproofing stage of the operation.  And finally, lay a reinforced mortar bed (screed) and install ceramic tile or stone on top of it.  The mortar bed is sloped away from the building to facilitate water run-off.  The "pitch" of this slope is typically 1/4 inch per running foot or slightly less. Water does move off the roof but not before a significant amount of it soaks into the mortar bed.

The absorbed water near the surface of the installation will evaporate back up through the grout joints in the tile layer (the same way it entered) if it doesn't get replenished with new rainwater. The moisture that accumulates below, however, will be stored and added to as more water arrives.  The mortar bed soon reaches the point of saturation, and the accumulated water is forced out the edges of the installation. Moisture oozes out and runs down fascia boards and either onto the walls below or onto the ground, eroding the roofing material as it courses toward the edge and ultimate escape.  This is if the roof deck was sloped to begin with which is not always the case.  If the roof deck is level under the mortar bed, water pools in low spots waiting for an opportunity to seep through to the living space below.

That was the state of the art until relatively recently, when a company by the name of Schluter Systems arrived on the scene with an innovative product called "Ditra." The Ditra tiling membrane provides a stable surface for tiles to be set onto, and at the same time it affords the ability to waterproof the SURFACE of the tile installation. I said that Ditra is "relatively" recent. It's been around over 20 years. Following are a few pictures from a project we completed in Katy, Texas, in 2004.

The balcony is first floated with cement mortar in the conventional manner.

Ditra is installed over mud bed with thin set (dry set mortar).
If the membrane were being installed directly to plywood, modified mortar would be used.

Ditra is cut closely around posts and caulked with silicone sealant.

For waterproofing, seams are covered with strips of Kerdi membrane.

Cut strips of Ditra are used as flashing. They are sealed to the floor with Kerdi.

Tiles are installed on Ditra using dry set mortar.

Floor is grouted and cleaned.

For additional information on Ditra floors see Ceramic Tile Floors - Ditra.

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