Pre-sealing is the process of sealing a tile or stone before it is installed and helps protect the tile from installation water damage such as that caused by grouting between the tile joints. Pre-sealing also helps reduce the amount of impregnating sealer required once the tile is installed as it reduces the amount of sealer penetrating too deeply into the tile. One other important benefit of pre-sealing is to reduce the effects of grout migrating into the side of the tile causing an unsightly discolouration. Some tiles arrive on the job already pre-sealed, often with a relatively weak sealer in the factory. To check if a tile needs to be pre-sealed, place a tablespoon of water on it's surface for 30 seconds. Blot up the water with a tissue, pressing hard to soak up any water in the texture of the surface. If the water is absorbed or leaves a dark mark the tile should be pre-sealed prior to their laying. Pre-sealing the sides of a tile is not an issue since a strong bond between the grout and the tile is not essential. The main purpose of the grout is to fill the gap and provide lateral support. Both of these outcomes are achieved by pre-sealing the edge of the tile.