What is the difference between rectified and non-rectified tiles?

Rectification is a process that affects the edges of a tile. A mechanical process straightens the tile edges and ensures they are perfectly squared. So, all the tiles are exactly the same size and can therefore be laid with a minimum grout joint of 2 mm. Non-rectified tiles, on the other hand, are tiles with natural, uneven edges that require a wider grout joint of 3 mm.