QUESTIONI am a remodeling contractor, having just completed a bath renovation project including a fully-tiled shower. The tile used was a standard 3x6 "subway tile" laid running bond with small joints (lugged-type; probably 1/6"). I typically require the inside corners to be held a bit wider; perhaps 1/8" for caulk joints. This is white tile with a silver-gray ground (and matching caulk), so the joints are prominent.
My client has complained about the width and variation of the width of the vertical inside (caulked) corner joints. Hard to measure an inside corner, but I approximate that the joint width may vary from approx 1/8" to just shy of 1/4" width between top and bottom of the 6.5' tall joint.
Are there industry standards for tolerances in these types of joints?
ANSWER - You are correct to install caulked movement joints at the perimeters and inside vertical corners of the tile installation. Caulk should be an ASTM C920 silicone sealant per TCNA EJ171 standards.
The ceramic tile industry doesn't have a clear standard for what the tolerance should be for grout joints and movement joints. It only subjectively states: "Nominal centerline of all grout joints shall be straight with due allowances for the variations in the respective tile being used."
I recently submitted a standard for consideration to the ANSI A108 committee that states:
"184.108.40.206.3.1 Movement sealant joint widths will vary more or less during the tile installation as the installer attempts to compensate for the natural inherent variations in the tile sizing. Nominal centerline of all movement joints shall be straight with due allowances for the variations in the respective tile being installed. In no circumstances shall the movement joint width vary more than +/- 25%."
The Marble Institute of America Design manual states that Joint Width Tolerance is the greater of either 1/16" or 25% of the specified joint width when installing stone.
ASTM C1472 Standard Guide for Calculating Movement and other Effects When Establishing Sealant Joint Width, states: Tolerances allows +/- 1/16” variation in the width of prefabricated joints and as much as ¼” variation in the width of job site installed joints.”
Based on the above, your case having an intended 1/8" wide movement sealant joint the variation should not be more than +/- 1/32" to 1/16" or wider than 5/32" to 3/16".