The technical specifications for tiles include reference to the Porcelain Enamel Institute (PEI) and Mohs ratings, but what are they and what do they reflect? Understanding these two measures can help determine the best choice of tiles for a particular application, particularly for commercial projects. 

What is the PEI rating? 

The PEI wear abrasion test is used to classify tiles according to the field of use, and the expected type of traffic and abuse the tile is likely to experience. It is a wear rating specifically for glazed ceramic tile surfaces.  

• PEI 0 tiles are unsuitable for use on floors.  
• PEI 1 and 2 are for use in areas with softer, abrasive, dirt-free footwear such as bathrooms and bedrooms, often high-gloss or intensive-coloured tiles.  
• PEI 3 is for areas in contact with normal footwear, including heavier residential traffic, but without dirt and grit action such as hallways and kitchens. 
• PEI 4 is for most residential floor areas and tiles suited to public areas, where moderate to heavier traffic occurs, i.e., hotel lobbies, restaurants and retails spaces.  
• PEI 5 is for the busiest commercial traffic floors. These tiles are chemically more resistant and are categorised as a hyper-resistant glaze. 

Mohs rating versus PEI rating 

While PEI measures the wear rating of a tile, the Mohs rating is used to identify a tile’s resistance to scratching. A tile sample is tested by pulling minerals with predetermined hardness ratings across the tile face. The mineral that succeeds in scratching the tile determines its rating. This test is commonly performed on glazed tiles, but it can also be used to determine how easily polished porcelains or other specially finished tiles will scratch. 

The higher the rating, the more scratch-resistant the tile. A rating of 7 or more is preferable as this is quartz, a primary raw material in ceramic tiles. 

• Mohs 1: Talc – resilient flooring. 
• Mohs 2: Gypsum – wood flooring.  
• Mohs 3: Calcite – polished marble, laminate flooring. 
• Mohs 4: Fluorite – black marble. 
• Mohs 5: Apatite – glazed ceramic tile. 
• Mohs 6: Orthoclase/Feldspar – glazed ceramic tile. 
• Mohs 7: Quartz – quarry tile, glazed porcelain tile. 
• Mohs 8: Topaz – unglazed porcelain tile. 
• Mohs 9: Corundum. 
• Mohs 10: Diamond. 

Bright glossy glazes do not usually offer particularly good surface hardness (5 to 5,5), while matt products or products with surface crystallisation may reach and exceed a Mohs value of 7. Much like cars, lighter colours generally hide scratch marks better than darker colours. 

Knowing the PEI and Mohs ratings of a tile helps to determine the best fit-for-purpose choice for different areas within a project. 

 Full acknowledgement and thanks go to http://mmsausa.com/ for the information in this article.