The ISO Technical Committee, ISO/TC 189, develops international standards for ceramic tiles and related installation materials which include test methods, definitions, specifications and classifications. In the U.S., we have our own domestic standards which are intended for the North American marketplace. But these international standards are important because they serve to unify global industry and facilitate international trade. In other words, international standards allow our industry to speak a common language worldwide regarding product performance.

Recently, a major revision was made to an important standard under the jurisdiction of ISO/TC 189, ISO 13006 which establishes the international specifications for ceramic tile. This revision was the first to this document since its inception in 1998. The following is an explanation of the changes.

Definitions for porcelain tile and rectified tile


Figure 1. ISO 13006 Requirements for Back Feet (If Specified)  If back feet are specified for a ceramic tile, the back pattern shall consist of parallel ridges with a dovetail. A dovetail simply means that L0 is greater than L1, L2 or L3 in any of these three examples.

Believe it or not, until recently, ISO 13006 did not define the terms “porcelain tile” or “rectified tile.” In fact, there was no mention of these words anywhere in the specification. It goes without saying that these terms are used widely and often throughout the worldwide industry when describing and specifying tile. Therefore, the following definitions were added to ISO 13006:

• Porcelain tile: fully vitrified tile with water absorption less than or equal to 0.5%, belonging to groups AIa and BIa (of ISO 13006).

• Rectified tile: ceramic tile that, after firing, is subjected to a precise mechanical grinding of the edges.

The standard also defines rectified tiles as being more dimensionally consistent than the criteria currently established for length and width, straightness of sides and rectangularity of non-rectified tiles. However, specifications or criteria for such consistency have not yet been established. By defining the term “rectified tile,” ISO/TC 189 has only taken the first step towards facilitating better specification of rectified tiles worldwide. The Committee fully expects that the next revision to ISO 13006 will establish tighter dimensional criteria for such products, likely similar to those which have already been established by North America’s ANSI A137.1 standard.

New category of tile: extruded porcelain

ISO 13006 divides ceramic tiles into groups according to their method of manufacture (extruded or pressed) and their water absorption. Strength and performance requirements for a tile are dependent upon which group that tile belongs to.

For pressed tiles, the highest water absorption group has always been BIII, or tiles with water absorption greater than 10%. The lowest water absorption group has always been BIa, or tiles with water absorption less than or equal to 0.5% (i.e. porcelain). There are also several intermediate groups for pressed tiles based on water absorption.

For extruded tiles, the highest water absorption group has always been AIII, or tiles with water absorption greater than 10%. Until now, the lowest water absorption group was AI, or tiles with water absorption between 0.5% and 3%. There was no group specified for extruded tiles with water absorption less than or equal to 0.5%, or extruded porcelain tiles.

In the newly revised ISO 13006, a new group and strength and performance specifications have been established for extruded porcelain tiles: Group AIa, extruded tiles with water absorption less than or equal to 0.5%. 


For larger pressed tiles, caps on the allowable percent of dimensional variation keep requirements reasonably stringent.


Indication of post-fire surface applications

Some manufacturers add waxes, sealers or other organic coatings to the surfaces of tiles after they have already been fired to impart certain benefits. However, in some cases these organic coatings don’t last.

Additionally, many green building standards do not require that tiles be tested for Volatile Organic Compound (VOC) emissions unless post-fire surface applications have been made. In order for specifiers to know when a test might be required, declaration of such an application by the manufacturer is necessary.

ISO 13006 marking requirements for tile and/or packaging now state that the manufacturer shall indicate any surface treatment applied to a tile after firing.

Also, ISO test methods for stain and chemical resistance will soon require that post-fire surface applications be removed prior to testing, and laboratory technicians will now know when to follow this procedure.

“Back feet” specifications

New to ISO 13006 are criteria for tiles which possess dovetail back patterns, or “back feet.” This revision does not establish a new requirement for all tiles, but rather, it introduces product design criteria which are to be followed where back feet are specified. For example, some tunnels or exterior facades, especially those in earthquake zones, may specify the installation of tiles with back feet.

The ISO 13006 definition for back feet is as follows:

  • Back feet: parallel ridges running across the back surface of some exterior wall tiles which possess geometry intended to facilitate an interlocking connection between the tile and cement mortar.
  • If back feet are specified for a ceramic tile, ISO 13006 requires that at least a slight dovetail be present in its back pattern. See Figure 1 for an illustration of this requirement.

Tighter dimensional tolerances

The recent ISO 13006 revisions also include updates to dimensional criteria. Criteria for length and width consistency, thickness consistency, straightness of sides, rectangularity (how close to 90 degrees each corner is), and surface flatness have been made more stringent for pressed tiles. 

Previously, tolerable dimensional variances for a tile were based on percent deviation from that tile’s intended size. For example, for a 300- x 300-mm (12- x 12-inch) pressed porcelain tile, the requirement was that the tile’s length could not deviate more than 0.6%, or 1.8 mm, from 300 mm. Expressed as a percentage, this tolerable variance was problematic for larger pressed tiles. For example, under the old requirement, a 600- x 600-mm (24- x 24-inch) pressed porcelain tile was allowed to have edges deviate by 0.6%, or 3.6 mm (over 1/8 of an inch!). Today, in addition to percentage limits, ISO 13006 incorporates maximum limits. For the example, just given the maximum allowable variation is 2.0 mm.  

Maximum limits have been established not only for length and width consistency, but for all pressed tile dimensional criteria. For larger tiles, these maximum limits function as caps on the allowable percent variation so that tolerable dimensional variance remains reasonably stringent.

In summary

ISO standards are important because they impact product performance in the international marketplace. Recent revisions to the international specification for ceramic tile, ISO 13006, are the first in over a decade. These revisions should result in a more up-to-date and globally applicable standard which better communicates product expectations in today’s world.