By: Ivy Yuan
Tile finishes offer an opportunity to create beautiful designs filled with color for a lasting impression. Tiles with low porosity are ideal surface coverings for exterior applications, provided that proper installation systems are used and stringent structural and physical requirements are met, which can be done with frequent building envelope surveys.
To avoid damage from freeze/thaw moisture expansion and to limit efflorescence, proper exterior tile installation should allow water to drain from the system before either the tile or the layers below the tile can absorb it. Since most tiles rated for exterior use are water impermeable, water can only infiltrate the system through the grout joints or the substrate itself. To avoid water collecting on the surface, balconies must have a minimum slope of approximately 1/4” per foot. If a balcony does not have a suitable slope, a sloping screed can be installed underneath the waterproofing layer. A screed is a thin layer of cement paste applied to a concrete floor base to act as a smooth flat surface in preparation for laying the final floor finish. Additionally, the balcony surface should be dry, load-bearing, crack-free, level, and free of any substances that may prevent the tile from adhering.
Expansion joints must be designed into the system to allow for movement. Outdoor floorings are constantly exposed to the elements, and therefore variations in temperatures and exposure to moisture. Direct sunlight, freezing temperatures, snow, rain, ice buildup, etc. will potentially cause mechanical stresses. If the outdoor tiles do not have room to move, grout will crack, and tiles will pop out. According to the Tile Council of North America, an expansion joint in outdoor tiling must be installed every 8 to 12 feet, in each direction. There also needs to be an expansion joint in the tile, if there are joints in the concrete slab underneath the tile. Expansion joints must also be installed around the perimeter of the tiled surface, and between different building materials, to prevent the formation of cracks.
When installing tiles, voids must be avoided to prevent water from being trapped. The ANSI Standards and the Tile Council of North America state that the average contact between the tile and the substrate should be about 95%. If this is not achieved, voids that trap water will form. This trapped moisture can eventually cause problems ranging from efflorescence to cracking. The National Tile Contractors Association provides the correct trowel techniques for setting tile, and demonstrates how to create a stronger bond between the tile and substrate.
Efflorescence produces unattractive white deposits around tile joints. Slight traces of efflorescence are most likely the result of deteriorating tile grout. At this early stage, the damage can easily be repaired by renewing and resealing with a cementitious grout, and performing regular maintenance to prevent the deterioration from reoccurring.
Severe efflorescence or spalled tiles are signs that water infiltration has caused more extensive damage. Water has most likely penetrated the tile assembly through cracked mortar joints, deteriorated tile grout or tile that is not frost resistant. If there are voids in the tile installation system, the infiltrating water can fill these voids, causing the spalling to worsen. The balcony can be more easily renovated, and these issues more readily mitigated, as long as the slope is correct, the tiles are moisture resistant, and the tiles are firmly adhered to the substrate. If this is not the case, more extensive repairs would include: removing all tiles and waterproofing, installing a new concrete substrate, applying new waterproofing, and installing exterior rated tiles that are properly adhered.
All too often, structural damage to balconies occurs despite the innovation in building materials and installation methods. In worst-case scenarios, the complete structure needs to be removed and replaced. These situations can be avoided if one is aware of proper installation methods, and takes the proper preventive measures.