Today, the standard method for tile production involves dry pressing ceramic raw material in a mould, and firing it in a kiln. During the firing stage, variation in heat and humidity can cause slight variations in the length and width of the finished tile. Traditionally a larger grout join has been used to accommodate for the size variations found in unrectified tiles (also known as a pressed tiles).
Rectified tiles are initially produced as a pressed tile, with an added step at the end of the manufacturing process. Rectified tiles have their edges ground down to a specific size with exact measurements. Today, the exact proportions of rectified tiles facilitates installation with minimal or extremely fine grout joints - resulting in huge advantages for installers, designers and end users.
3mm or less is now common and can be used to ensure the tile design remains uninterrupted by harsh grout lines that can sometimes detract from the desired look. A 1.5mm grout line can give an almost seamless appearance with the right tile and grout choice. By minimising the grout join and using a larger format tile, less grouting material is also required.
Glazed ceramic tiles and porcelain tiles are inherently hygienic materials, resistant to stains, bacteria and chemicals. Only the grout join remains as a potential home for bacteria and mould if not maintained properly. By installing rectified tiles to ensure a minimal grout join, the amount of cleaning required by the end user is kept to a minimum while creating a healthier, more hygienic surface.
Rectifying tiles also solves another inherent characteristic of kiln fired materials, tension. Tension occurs during the heating and cooling of ceramics; when the raw material particles fuse together to become a single solid mass. This tension can cause issues for tilers during installation when attempting to cut tiles, especially in (now common) large format tiles. When a cut is made into an unrectified tile, tension can be released instantaneously in the form of a crack as it attempts to leave the tile body through the path of least resistance. By rectifying tiles during the manufacturing process, the tension is released allowing for much easier installation with much less risk of cracking during cutting.
Rectification was once seen as an extra step in the manufacturing process but has become the norm rather than the exception due to the many benefits it gives installers, designers and end users.