Specification

TB87
GROUT JOINT WIDTH: WHAT IS THE RIGHT SIZE?
Technical Bulletin
Technical Services 800-282-8786
custombuildingproducts.com
All ceramic and natural stone tiles are installed with a
gap or space between each tile in the assembly. This
is generally referred to as the grout joint. However, the
required width of a grout joint is not always
understood. ANSI defines the requirement for grout
joints in ceramic and natural stone tile installations in
A108.02 Section 4.3.8. This section states that under no
circumstances should the grout joint be less than 1/16"
(1.6 mm).
Due to the amount of size variation in the tile, the
actual grout joint width may need to vary from what is
requested or specified. The actual grout joint size
should be equal to three times the variance in actual
tile facial dimensions. This means that if the variance in
facial dimensions of the tile is 1/8", the actual grout
joint will need to be 3/16". The wider spacing will help
to accommodate placement of tile and maintaining
straight lines.
TCNA recommends a minimum 1/8" grout joint for
rectified tile and minimum 3/16" grout joint for
calibrated tile. They also suggest adding to this width
the amount of edge warping on the longest edge. For
example, if the edge warping of a rectified tile is 1/32",
the minimum grout joint is 1/8" + 1/32" = 5/32".
To minimize lippage, TCNA also recommends no more
than a 33% offset for tile greater than 18". Large format
tiles (those with one or more sides longer than 15")
should be installed in a running bond or brick pattern,
especially if the tile is plank-shaped.
Where is the right place to measure the width of the
grout joint? With cushion edge and beveled edge
tiles, some will argue that the measurement is at the
surface of the tile or the widest point of the bevel. This
may minimize the grout joint appearance, but the joint
between the tiles is now too narrow to accommodate
proper filling and curing of the grout. The grout joint
width measurement should be taken at the base of the
bevel or at the body of the tile. ANSI states in A108.10
Section 5.3 that grout joints between cushion edge
(beveled) tiles should be finished evenly at the depth
of the cushion (bevel). This implies that the minimum
1/16" joint width is measured at the base of the cushion
or bevel.
Some tiles have lugs or tabs built into the edge of the
tile to assist in even spacing. If these lugs do not
produce a grout joint in compliance with TCNA
recommendation, additional separation may be
needed. Also, the space between the lugs and over
the lugs may not be sufficient for proper curing of the
grout and can result in powdery or discolored grout.
Extra care must be exercised when installing tiles with
spacing lugs on the edge.
Why is adequate grout joint width so important? First
and foremost, it will prevent tripping and breaking the
edge of the tile. By increasing the spacing between
the tiles, it reduces the slope of the transition from one
tile to the next tile. The wheels of carts roll freely over
the tile surface and shoes are less likely to catch on a
tile edge. Wider grout joints allow the installer to force
the grout deeper into the joint between tiles,
completely filling the grout joint. The larger mass of
grout will cure more completely and result in a harder
grout joint. Grout that is placed in joints that are too
narrow will be powdery and generally discolored.
Before the tiles are set, the required grout joints should
be discussed with the customer and agreed upon.
Properly spacing the tiles and selecting the correct
grouting material will assure an attractive, safe tile
installation that will last for years.
The information in this bulletin is presented in good faith, but no
warranty, express or implied, is given nor is freedom from any
patent in as much as any assistance furnished by CUSTOM with
reference to the safe use and disposal of its products provided
without charge. Custom Building Products assumes no obligation or
liability therefore, except to the extent that any such assistance shall
be given in good faith.