Indoor vs. Outdoor: The Importance of Tile Porosity in Extreme Conditions

The freezing temperatures will cause the water to expand which pushes upward and is absorbed by the porous tile, causing the face of the tile to spall.

Photo: Scott Carothers

Not all tile is created equal. This is not to infer that we are talking about the size, shape or thickness, but rather the durability of the tile in extreme environments.

Consumers often make their tile selection based on the color or shading. While this is a very important decision, the more significant consideration is where the tile will be installed. If the tile is being considered for an outdoor application, the next consideration should be whether or not the location is subject to winter weather in a freeze and thaw environment.

The American National Standards Institute (ANSI) A137.1 American National Standards Specifications for Ceramic Tile lists five tile classifications. Not all of them would be able to function well in temperatures subject to freeze and thaw conditions. The key to selecting the right tile for the job has to do with the porosity of the tile. Within this standard, there is a list that shows the porosity of each classification. This is the ability or lack of ability to absorb water.

Impervious tile, which includes porcelain tile, would be less than 0.5%. This means that the tile will only absorb less than one half of one percent of its weight in water, which is extremely small. The next category is vitreous tile which is 0.5% to 3%. This would include many but not all quarry tile products and some pressed floor tile (ceramic) products. This is where it can be tricky to determine if the selected tile meets the requirements of freeze/thaw applications. This information is best found in the tile manufacturer’s product data sheet. If it doesn’t specifically state that the tile meets these requirements, then most likely it would not be a good choice. When in question always contact the tile manufacturer and get the answer in writing. This will protect the tile contractor in a failure situation.

The other crucial part of an exterior installation is the amount of mortar coverage and transfer to the back of the tile. Again, the ANSI requirement for wet areas (i.e., showers) and exterior applications, the mortar coverage must 95%. If the trowel notches are not collapsed by moving the tile back and forth perpendicularly to the trowel ridges, hollow spaces will be present. The resulting mortar voids will trap water from the atmosphere and hold it, causing a two-fold problem. The freezing temperatures will cause the water to expand which pushes upward and is absorbed by the porous tile. The result of these two components is the spalled face of the tile – a failure and another black eye for the tile industry.

Before you say yes to an exterior tile installation, do your homework. Think about it!

Scott Carothers is the Director of Certification and Training for the Ceramic Tile Education Foundation headquartered in Pendleton, SC, and is responsible for the creation of the Certified Tile Installer (CTI) program, is involved in the creation of the new Advanced Certifications for Tile Installers (ACT) program as well as providing training to others in the tile industry. He has been involved in the ceramic tile industry for over 33 years and was the owner of a successful retail firm prior to coming to CTEF. He has served as President of the NTCA, Chairman of the NTCA Technical Committee and named the NTCA Tile Person of the Year in 2005. He is a voting member of the ANSI and the TCNA Handbook committees. He may be contacted at 864-222-2131 or scott@tilecareer.com.