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MAPEI Tech Talk is a blog devoted to the flooring and construction industry. It is updated on a regular basis by the social media team at MAPEI Americas, and it will feature guest bloggers occasionally as we provide you with viewpoints from across the industry.
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Jim is MAPEI’s Technical Services Manager and has been active in many industry committees over the years.
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February 25, 2016 - 17.11
Spot Bonding—What Are the Drawbacks When Installing Tile or Stone?
by Jim Whitfield
Spot Bond Method -Signs of Discoloration on the Face of the Stone Tile
Spot bonding has become a growing problem for the tile industry. Larger tiles and narrow grout joints make leveling a finished tile floor a challenge. The reason why spot bonding is getting more popular is lippage, large tile supported by 5 daubs of mortar under them can be pushed down corner by corner till reasonably level. The problem is this method has lower impacts strengths, lower load resistance, lower shear strengths and failed tile installations.  Installation problems that result from inadequate mortar coverage or 'spot bonding' can cause catastrophic issues, safety concerns, loss of reputation and costly repairs. 

Tile can be very competitive with another flooring when considering the life cycle of a properly installed quality tile installation. If the substrate needs preparation, do it correctly. Surface preparation is the foundation of your installation. The ANSI requirements for substrate deviation for tile with at least one edge greater than 15” (large format), the maximum allowable variation is no more than 1/8” in 10’ and no more than 1/16” in 2 feet from the required plane, when measured from the high points in the surface. The substrate must be flat for large format tiles.

While there is one method in the TCNA Handbook for spot bonding with an epoxy adhesive, it states “will not withstand impacts”, lists other limitations and is for certain interior wall conditions only. Cement based mortars are intended to be used to directly adhere tile with continuous coverage. ANSI requires interior installations to have a minimum of 80% coverage of the thin-set mortar between the tile and the substrate.

For exteriors, a minimum of 95% coverage is required. The fully supported tile has much higher shear, impact, and compressive strengths.In addition to the previously listed issues, discoloration of stone tile is common in spot bonding. This can occur by either the bonding method looking different than the field or water accumulating behind the stone tile at the bottom of a wall, leading to leaks, water damage, and unsightly stone tile installations. Grout will not be supported in a spot bonded installation allowing a path for water to get behind the installation. This method has grown from larger format tiles, tighter grout joints, and unacceptable substrates. While these are constant challenges, spot bonding is not the answer. It is a failure just waiting to occur.
Youtube Video below:  In a San Jose, CA subdivision, tiles are falling off of the exterior facade of these million dollar homes.
 
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