We were awarded a large office building project in California. The lobby floor tile is 5,000 sq. ft. of 24” x 48” porcelain over a mortarbed. The architect is calling for a 1/16” grout joint. During your seminar last summer, you educated me about how this is not a good thing, since there is expansion within the tile itself. Do you have some literature or could you tell me where I can get some stating this, so I can submit it to the architect and get them to change it to a 1/8” joint?
Minimum grout joint size is addressed in both the TCNA Handbook for Ceramic, Glass and Stone Tile Installation and in ANSI. It is found on page 37 in the 2018 TCNA Handbook section entitled, “Grout Joint Size, Layouts, and Patterns,” which is excerpted from ANSI A108.02-2017, section 4.3.8.
The Handbook states:
“To accommodate the range in facial dimensions of tile supplied, the actual grout joint size shall be at least three times the actual variation of facial dimensions of the tile supplied. Example: for tile having a total variation of 1/16” in facial dimensions, a minimum of 3/16” grout joint shall be used. Nominal centerline of all joints shall be straight with due allowances for hand-molded or rustic tiles. In no circumstance shall the grout joint be less than 1/16”.”
It goes on to give an example of tiles that vary in size in running bond/brick joint patterns, calling for a minimum of 1/8” wide grout joints for rectified tiles and 3/16” wide grout joints for calibrated tiles with any side greater than 15”.
Generally speaking, under this standard, most calibrated tile should not have a grout joint smaller than 3/16”. Most rectified tiles should have no grout joint smaller than 1/8”. The smallest grout joint you should ever have is 1/16” and is usually only applicable in stone installations.
I hope this helps.
– Robb Roderick, NTCA Technical Trainer