Avoiding leaky exterior tile decks

The other theory is since water is going to penetrate the grout lines and get under the tile, a drainage plane needs to be provided to allow its escape. This brings up some other issues, such as the method of fastening the drainage mat (with a thin-set bonding adhesive, but not necessarily the same one used for the tile). Following the manufacturer’s recommendations is essential for success and to ensure warranty coverage. (It is important to ensure the waterproofing membrane being used is covered with a warranty. Often, the warranty is void when it is covered by another product, like tile. Specific terms and conditions need to be checked with the manufacturer.)

The assembly has little tolerance for movement and is likely to crack if there are not steps to reduce (isolate) the movement of the subsurface from the tile/grout assembly. Waterproofing membranes likely provide some crack isolation themselves; this protection is increased by adding a drainage/decoupling mat.

Critical installation details
There are a few finish details that are critical to a successful waterproof tile deck.

Outside perimeters
Since there are many ways to finish a tile deck’s outside perimeter, the design team needs to establish the desired look, consulting with the owner, builder, and tile-setter. Depending on the chosen finish, the details can be altered accordingly. Attention to these details contributes to the job’s overall success.

Drains
Should drains be necessary, a special cast drain with a square top makes it easier and more attractive for the tile applicator’s finishing.

Rail attachments
As mentioned, this author strongly recommends attaching rails to the fascia instead of the surface of the deck. Rails installed over the tile will cause the overlay to crack. There are special details for surface mounted rails if there is no other alternative.

Inside perimeter
If the owner wants the tile to return up the wall as part of the finished look, appropriate flashings are needed. If not, then consideration must be given to the visibility of the part of the membrane that returns up the wall and hiding the gap that must be left on the inside of the tile application.

Surface preparation
Apart from a thorough inspection for a properly fastened substrate, there is little preparation work necessary. A light sanding of the joints of the cement board or a scraping of the entire surface to take care of any bumps will suffice; no filling is required.

Installation qualifications
A waterproofing membrane, especially in a roofing application over living space, should be installed by a qualified applicator who has gone through a training program, can work with the critical details as specified above, and, most importantly, understands proper roofing principles.

Conclusion
There are few outdoor surfaces as attractive and durable as tile or stone. They can be used outdoors even in extreme climates, providing there is a great deal of care put into the choices of materials and trades people.

As so often happens, attempts to cut corners on costs or by taking shortcuts—even ones that seem to make sense—result in the most expensive installations. The common theme is to follow the manufacturer’s recommendations to the letter and employ only experienced professionals for each part of the job. The chances of a successful, long-lasting installation exponentially increase when this occurs.

John Ogilvie is the president and co-owner of Duradek Ltd., which has been waterproofing decks and balconies since 1974. He helped develop a roof membrane specifically designed and tested for the application of tile or stone overlays. Nearly 40 years ago, Ogilvie also was a key figure in developing the industry’s first approved walkable vinyl roof deck system. He continues to certify journeymen installers and runs building envelope seminars across North America. Ogilvie can be contacted via e-mail at jogilvie@duradek.com.