Water absorption, ASTM C373-88
Water absorption is measured using ASTM C373-88. Individual tiles are weighed, saturated with water, then weighed again. The percent difference between the two conditions is referred to as the water absorption value. Tiles are classified according to water absorption percentages as follows.
Impervious: Tiles exceeding 0.5% or less
Vitreous: Tiles exceeding more than 0.5% but not more than 3.0%
Semi-vitreous: Tiles exhibiting more than 3.0% but not more than 7.0%
Non-vitreous: Tiles exhibiting more than 7.0%