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Stone Failures-Why? Article #11
Article #1, Article #2, Article #3, Article #4, Article #5, Article #6, Article #7, Article #8, Article #9, Article #10, Article #11, Article #12, Article #13, Article #14

Failure Number 11       Attachment of Wire To Wood Floor Assembly

There is no requirement in ANSI A108 or in Assembly Method F141 in the Handbook For Ceramic Tile Installation to mechanically fasten the 2-inch by 2-inch 16/16 gage reinforcing wire fabric, or equal, to the wood floor assembly.

Mechanically fastening the wire transfers the stress that occurs with moisture and thermal expansion and point load stresses occurring with weight transfer from the top of the tile or stone assembly.

Indent fracturing of the tile and stone floors are the first indication the wire was improperly attached to the wood framed floor assembly.

The failure is prominent in radiant heat floor systems when the wire is attached to the wood floor assembly.  The correct method is to install the radiant heat tubing, fill the spaces between the tubes in with mortar, install a cleavage membrane, and install a wire reinforced mortar bed, and stone or tile. We had one home in Rancho Santa Fe where the marble contractor installed stucco mesh underneath the radiant heat tubing and mechanically fastened the stucco mesh into the wood floor. The red travertine stone from Spain was installed.  I was called in when the red travertine stone from Spain started indent fracturing. The fracturing was occurring in 3-foot grids initially.  A lawsuit was filed. The Builder blamed the lack of wood floor assembly for excessive deflection. 

Destructive testing proved the wire was in the wrong location and was fastened improperly to the wood floor. By the time the lawsuit was settled, the indent fracturing was occurring as close as 8 inches apart.  The radiant heat tubing creates a weakened plane joint causing cracking of the mortar and resultant indent cracking and fracturing of the stone. The floor was replaced at a cost exceeding $250,000.  An expensive lesson to learn not to mechanically fasten the wire to the mortar bed and not to listen to the radiant heating engineer who said to place the wire underneath the tubing, instead of using a cleavage membrane and place the wire in the mortar bed above the radiant heat tubing.

Since this time, the Marble Institute of America has published the requirements for the wood floor assembly to achieve L/720 instead of L/360 as published in Assembly Method F141 in the Handbook For Ceramic Tile Installation.

We are in complete disagreement with assembly method F145 introduced in 1997 into the Handbook For Ceramic Tile Installation. We have investigated failures upon failures of wood floor assemblies where wire, expanded metal lath, and stucco mesh are mechanically fastened to the wood floor assembly.  Bob Stanaland, CTA with the Ceramic Tile Institute of Northern California has been investigating similar failures for years.  I have had correspondence with Robert Daniels of the Tile Council of America, Inc. and with Gray LaFortune, CTC with the Ceramic Tile Institute of America, Inc.

Robert Daniels response was the assembly is only for less than 100 square feet and contractors in the northeast portion of the United States claim they have been installing this method successfully for years. I question if the contractors have had the opportunity to go back and look to see if the installations are performing or failing.

When I served as a representative to the Tile Council of America Bi-Annual Handbook For Ceramic Tile Installation Conference, I documented the bonding to wood failures investigated by myself, while investigating at the Ceramic Tile And Marble Institute of San Diego, the Ceramic Tile Institute, and the Ceramic Tile Institute of America.  The purpose was to oppose Bob Moore proposing modified epoxy emulsion mortars as suitable for bonding to all wood assemblies. I have lawsuits today with failures of stone installed on floors and decks due to the mechanical fastening of the wire reinforcing to the wood framing.  The installing contractors who mechanically fastened the wire to the wood floor are now claiming the sole fault is the wood floor was not built to L/720 as now required by the Marble Institute of America.

I had discussions during attendance at a Ceramic Tile Distributors of America Convention in Texas with a concrete tile manufacturer sales representative. He stated their product is installed successfully with direct bond to plywood floors.  I related I was traveling to Boston to attend the American Society of Association Executives Annual Convention.  He related the bar in the hotel I was staying at had this installation.  In Boston, I visited the bar with concrete tile directly bonded to the wood floor.  The entire floor was failing with fractured tiles and grout. I followed up with a courtesy letter to the sales representative advising him of the failure observed.

This article is part of a series of articles on Stone Failures (Dec. 2000) by Greg Mowat

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