Water Absorption 101

Water absorption rates are the most important measurement of a tile. Water absorption measures how much moisture a specific type of tile is likely to absorb on an ongoing basis. Some types of tile may crack if the moisture penetration is too high. In general if the tile has a low water absorption, the durability and strength are increased. Low water absorption restricts the amount of water that may cause failure by cyclic salt attack and freeze thaw. The water absorption percentage reflects the density of the tile body. Water absorption is also directly related to the suitability for interior or exterior applications. For exterior applications, the selected tiles should have a low water absorption rate, especially in climates subjected to heavy rainfall and freezing and thawing cycles. A low water absorption rate also enables a tile to resist food or beverage stains.

Testing for water absorption determines the apparent porosity and relative density as a means to classify ceramic tiles according to the international standard ISO13006-10545/98. There are four categories:

• B2b. Non-vitreous - Low density, High water absorption of more than 6.0% (Ceramic)
• B2a. Semi-vitreous - Medium density, Medium water absorption of more than 3.0%, but less than 6.0% (Ceramic)
• B1b. Fully Vitrified - High density, Low water absorption of more than 0.5%, but less than 3.0% (Ceramic)
• B1a. Impervious - Extremely high density, Very low water absorption of less than 0.5% (Porcelain)

One thing to remember is that while porcelain is often viewed by the consumer as a superior product this does not guarantee that the material is fit for purpose, or put another way, it is unnecessary to use porcelain in an interior space with low traffic that is not exposed to extreme temperatures or water.

There are 3 methods to determine the water absorption of tiles:
Boiling method
Vacuum method
Electrical method

The boiling method is used to classify the ceramic tiles and involves drying the tiles out and then boiling them in water for 2 hours followed by cooling to room temperature over a four hour period. The mass of the tiles are weighed both before and after the water immersion to determine the percentage of water absorption.

The vacuum method evacuates the air from a chamber with the tiles inside and then immerses the tiles in water. Once again the tiles are weighed before and after water immersion to determine the apparent porosity, apparent relative density and bulk density.

The electrical method requires that the tiles be immersed in water for two hours then a high voltage electric current is passed through the tiles. The measured conductivity of the tile determines the percentage of water absorbed.

OK, those are the basics, take a look at our catalogues, select a few tiles and determine a suitable application. Ask your experienced staff to check or email us and we'll answer you.