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Ceramic Tile Cracks on Wood Floors

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We are researching the probable cause of tile and grout cracks when the tile is installed on wood floors.  We calculated the curvatures of the joists and floor sheathing for four assemblies in the TCA manual and found the curvature between joists under a 300 lbs. concentrated load to be about 10 times greater than the curvature of the joist under a 50 psf uniform total load. The following is the first paragraph from our paper:
 
Joist Curvature verses Sheathing Curvature and the Probable Role of Each on Ceramic Tile Performance
Introduction
The cracking of ceramic tile and grout is a common problem in residential floor applications.  Prior to 2001, the design criteria set forth by the Tile Council of America (TCA) in the Handbook for Ceramic Tile Installation stated “design floor areas over which tile is to be applied to have a deflection not greater than L/360 of the span” (TCA, 2000).  A common misconception among joist designers was that this L/360 deflection requirement in TCA was the same L/360 building code deflection limit for residential floor joists under a uniform design live load of 40 psf.  In 2001, the language of the provision was changed to “design floor areas over which tile is to be applied to have a deflection not greater than L/360 of the span when measured under 300 lbs. concentrated load (see ASTM C627)” (TCA, 2001).  Thus, in 2001, it became clear to us that there were two L/360’s involved and no known relationship between the two L/360’s could be established by engineering analyses.
 
If you would like to have a copy of our publication, please send a self-addressed stamped envelope (one stamp) to me at:
Frank Woeste
1502 Nelson Street
Blacksburg, VA 24060
 
We welcome your comments at any time.
Thank you, Frank Woeste
 
Our next short course:
Structural Design with Wood
September 16-18, 2003
www.conted.vt.edu/sdww/
 
Frank Woeste, P. E., Professor Emeritus
www.woodscience.vt.edu/resumes/woeste1101.pdf