Photos courtesy Hillside Decking
Railings
A surface-mounted rail should never be attached atop a tile or stone finish, as the fasteners required to hold the rails will penetrate the roofing membrane. Water flows on top of the waterproofing membrane, and any penetration will be almost impossible to seal.
The other issue with a surface-mounted rail relates to the likelihood of cracking the tile as the fastener is tightened. The best practice is to mount the rails on the fascia or on a curb.
If the rails are mounted on posts that penetrate the deck surface, special provisions must beSome thin-set manufacturers recommended regularly applying the appropriate sealer to the tile and/or the grout. Their rationale is this reduces the penetrating moisture and helps prolong the assembly’s life.
This author knows of a contractor in the San Francisco Bay area who recently completed a repair of a failed residential tile job that involved a new ceiling, replacement of rotted floor joists, door removal, and a new tile installation, this time with an appropriate roofing membrane. The problem was a waterproofing membrane had been present, but it was not a ‘roofing’ membrane or installed with ‘roofing’ details. The repair was more than $70,000 for a deck that was only about 46.5 m2 (500 sf). It could have been avoided by spending an extra few dollars per square foot to have a proper, tile-compatible, roofing membrane installed in the first place.
Preventing failures
A major cause of failure of tile over decks and balconies is the structure to which it is applied allows too much deflection. Tile has little tolerance for deflection, and cracking grout lines or units is the result.
Photos courtesy Duradek
Deflection is a product of the joist spacing and thickness of the flooring materials. The TTMAC specification for flooring under tile or slate (i.e. Exterior Decks 325ED–2009/2010 Detail C) notes:
Sub-floor—16-mm [3⁄5-in.] exterior-grade plywood meeting, sloped a minimum of 2%. Backer unit 13 mm [1⁄2 in.] minimum and must be exterior-rated. Backer unit bond-coat and fasteners as recommended by manufacturer. Backbuttering recommended to bond tile to achieve 95% mortar contact.
Apply approved roofing membrane and primer as recommended by manufacturer.
The use of a cement board overlay is recommended by most tile associations and manufacturers, but it is important to remember there may be regional differences. Cement board, unlike plywood, is not affected by varying levels of moisture. Indeed, for the money being invested in the whole system, it would seem unwise to scrimp on the subsurface. In case of a failure (i.e. cracking), the first thing anyone will look at to lay blame is whether the floor was strong enough and provided the necessary deflection resistance. Concrete decks and balconies are suitable for tile application, but still require proper waterproofing or roofing protection.
Sloping the surface Puddles are both annoying and a potential source of damage to the tile assembly. The easiest way to direct water away is via adequate slope. Nevertheless, sound roofing/waterproofing practice needs to be employed even when tile is applied over top. One should operate on the expectation of water getting through the tile installation. The waterproofing membrane will be applied to a surface sloped toward drains, scuppers, or an outside edge that allows water to escape.
Moisture will still run downhill, even under tile applications. This can happen without negatively affecting the bond of the thin-set mortar to either the tile or membrane. If there are seams in the waterproofing membrane, they should run parallel to the slope to avoid any puddling water behind the bump.
A two-percent slope (i.e. approximately 63.5 mm [2.5 in.] in 3 m [10 ft]) is safe. Many people consider this excessive and try to reduce it, only to find that with settling of the building, frame shrinkage, and the possibility of the crowns on the floor joists not all being up, there are puddles.
While it is possible to provide a slope to a flat, waterproof surface with thick-set mortar, there are problems to consider with this decision. If the waterproof membrane is flat or allows water to pond on it, providing a sloped mortar bed will not remove all the water from the deck. Although most of the moisture will drain off the top surface, water can still enter under the tile through cracks in the grout joints, cracks in the tile, or on perimeters.
The water that enters will follow the waterproofing membrane’s slope. If it ponds before the thickset mortar goes on, it will also do so after the tile job is completed, potentially causing mold and an unpleasant odor.
Any ‘bellies’ or depressions need to be taken out of the deck surface before the waterproofing membrane is installed. Since water will not penetrate the waterproofing membrane, if the depression has been eliminated any water reaching it will be shed away.
In the front of my house I have a second floor balcony off of my bedroom. The out door balcony has a tile flooring and no roof above. When it rains there is a leak coming from tiles and the drain. Water is leaking down into ceiling onto floor outside the front porch near front door on ground level.
I have the same problem as Michael Lawson