Grout is generally a material that fills the spaces between tiles to prevent debris, dirt and contaminants from settling in between the tiles. It is normally made using cement as the effective binder but may have other constituent parts for specialised environments. It also forms an effective barrier to water seepage under the tile, where it can loosen the tile adhesive or mortar. Without grout or with the ineffective application and maintenance of grout, water can soak into the substrate and cause rot, mould or mildew. Generally powdered grouts are mixed with water in a bucket, then applied using a rubber tool called a float. After the grouted lines dry and harden a barrier forms between the tiles to protect the substrate and tiles.
Grouts come in a variety of colours to suit taste and room colours. Not all grout is the same. The type of grout that will best serve your needs depends upon various elements which characterise your application. These typically include whether the tiles are to be affixed to wall or floor, upon solid or flexural substrate, in wet or dry areas and in areas of light or heavy footfall.
Unsanded Grout - ''Unsanded'' grout literally means the grout does not contain sand. It is generally made of Portland cement and colouring pigments. Unsanded grout is used between tiles that are set 3mm or less apart from each other. Filling narrow spaces requires a mixture that does not contain even fine aggregate,which may hinder the complete filling of the spaces between the tiles. The modern trends of using very large format tiles with the minimum of spacing sometimes dictates that unsanded grout is pre-requisite. It is most often used in areas where small spacing is desired such as tiled worktops etc. Also If you have polished natural stone or glass tiles, set them closely so you can use unsanded grout, sanded grout will be abrasive on the tile surface and cause scratches.