Table 1: ISO Classification System

Standards are authoritative. They give us a means for testing and evaluating. They set out rules to define what is normal, what meets expectations and what doesn’t. ANSI and ISO standards and testing for tile setting mortars are two halves of a puzzle for the tiling industry-two halves that can help us get a better synthesized picture of what is going on underneath all of those tiles being laid everyday around the country.

And yet, how can we have two standards for the same thing? The answer lies in multiple perspectives, and sometimes two perspectives are better than one, just like heads.

What's the history behind these standards?

A working draft of the ISO standard for tile setting mortars, 13007, was finalized with the help of ANSI committee participants early in the year 2000. The standard was important as the tile market grew transnationally. As the ISO standard was being developed internationally, the United States largely continued to use the domestically developed ANSI standards, parts of which were drafted nearly fifty years ago and have been regularly updated.

The ANSI standards, which for tile setting mortars are 118.1, 118.3, 118.4, 118.5, 118.8, 118.11and 136.1, have been the main way Americans have understood tile setting mortars for a long time now. In the 2011 TCA Handbook, the ISO standards will be placed alongside the customary ANSI standards for the first time. So, it’s important to understand what those specifications mean as they become more widely used and specified for tile setting mortars.

In case you’re unfamiliar with the ISO standard, according to the ISO website, it’s pronounced “iso” not “I-S-O.” ISO isn’t an acronym because it has to be used by multiple countries around the world, all of whom speak different languages. Instead, ISO is the Greek word for “equal,” which essentially embodies the goal of the International Organization for Standardization, to make all things equal for international businesses to function well across boundary lines.

What do the two sets of standards involve?

Both sets of specifications test to evaluate cementitious, dispersion, and resin based tile setting systems. Both standards use tests involving destructive mechanical analysis of the mortar, but in two distinct, but overlapping approaches. Additionally, both sets look at aspects of open time, sag resistance, and flexural strengths of mortars, albeit with slight differences. However, there is one central difference in which the tests specified in the standards evaluate the bond strength of tile setting mortars. The ISO tests make tensile measurements while the ANSI tests make shear measurements. More specifically, a tensile test pulls the tile vertically from the substrate and a shear test pushes the tile sideways off the substrate. Both measurements give good, but different, insights into how well the tile is bonded to the substrate.

For bond strength, the ISO standard specifies that the force to pull off a tile under a variety of curing conditions should be 0.5 MPa (approximately 72 psi) to earn a 1 rating and 1 MPa (approximately 145 psi) to earn a 2 rating. Meanwhile, the ANSI standard tests the resistance to shear, also under a variety of curing conditions, with typical values of 100 to 300 psi being required depending on the parameters of the tests.

Under the ISO system, letters and numbers are assigned to the tile-setting mortars based on their performance. For example, a C2S2P1E mortar is a cement-based mortar that has improved bond strength over concrete, improved deformability, normal plywood adhesion, and extended open time.

What's the end result of having two sets of standards?

These standards offer two different paradigms from which to view a tile setting mortar and an understanding of the different levels of performance that may be achieved among the wide range of tile setting mortars available.

Strangely enough, a standard is also another name for a flag that is carried into battle. Rather than thinking of these as two competing systems meeting on the battlefield of the US tile industry, we might think of them as partners in revealing the intricacies of how tile can be bonded.