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Stone Failures-Why? Article #8
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 8       Incorrect Backer Board Installations

Backer board installations not taped and properly installed will cause indent fracturing of the stone directly installed over the untapped joints between the backer board sheets.

Fastening of the backer board is required to follow the manufacturers installation instructions explicitly.

Failures including indent fracturing of tile, limestone, marble and granite installed over backer board installations without tape are occurring. One contractor I talked with after he removed and replaced, at his cost, an entire limestone floor over backer board installation, admitted he was in a hurry and left the tape off. This was an expensive lesson to learn.

I testified in trial in Colorado where the backer board was sold by a large home supply store to a builder. The home supply store did not sell the tape, and did not offer the manufacturers installation instructions.  The builder asked the limestone distributor if the limestone would crack.  The limestone distributor said no.  The builder installed the backer board, no tape, and used liquid nails to adhere the backer board to the wood floor. The limestone cracked and was fractured directly above each seam between each sheet of the backer board. The judge ruled in favor of the limestone distributor and the installer of the backer board failed to install the backer board correctly.

Backer board installation used in showers is in lieu of a wire reinforced mortar bed. The installation still requires a weather resistive barrier paper on all vertical wall assemblies and waterproof membranes over all horizontal wood framing.

Installation of backer board in showers directly to water resistant gypsum board is not an approved assembly and will contribute to water damage of the water resistant gypsum board backing in the shower assembly.

Some building jurisdictions have eliminated water resistant gypsum board as a suitable backing for direct bond of tile and stone in a shower assembly.

Sales representative of a major cement backer board company, that also makes water resistant gypsum board, has made claims representing the water resistant gypsum board division that are erroneous. However, they are in two competing divisions of the same company.  The sales method is not right, but the tile industry likes the end result to not bond directly to water resistant gypsum board unless some form of waterproof membrane protects the water resistant gypsum board. Type II mastic is not a waterproof membrane.

Recent investigations include backer board installations on countertops.  The backer board is not adequately installed with the wrong side up.  One recent project, we went into the kitchen and easily lifted the stone right off of the backer board.

The Ceramic Tile Institute of Northern California is currently cautioning against veneer installations utilizing backer board due to investigation of many veneer failures where installations were promoted and specified by the backer board sales representative.

Distributors selling the backer board should sell the tape and give manufacturers installation requirements or verify the contractor and employees have the manufacturers recommendations.

Contractors should inspect the backer board before installation of stone over the backer board. If you are a contractor installing backer board, follow manufacturers installation directions explicitly. Remember the Marble Institute of America requires L/720 for suitable substrate to receive stone installation on horizontal surfaces.

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

Forensic Tile Consultants
9541 Vervain Street
San Diego, CA 92129-3523
(858) 484-8118, Fax 484-8302

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