Grout is a dense fluid which is used to fill gaps or used as reinforcement in existing structures.Grout is generally a mixture of water, cement, and sand and is employed in pressure grouting, embedding rebar in masonry walls, connecting sections of pre-cast concrete, filling voids, and sealing joints such as those between tiles. Common uses for grout in the household include filling in tiles of shower floors and kitchen tiles.

It is often color tinted when it has to be kept visible and sometimes includes fine gravel when being used to fill large spaces (such as the cores of concrete blocks). Unlike other structural pastes such as plaster or joint compound, correctly mixed and applied grout forms a waterproof seal.

All natural stone tile flooring requires grout including slate, limestone, marble, travertine, sandstone, quartz, granite, and onyx. Clay-based materials such as ceramics, porcelain, brick pavers, and terracotta require the use of grout to prevent cracking, as do mosaic tile floors of glass, stone, or plastic. You also find grout lines being used decoratively in some resilient and concrete flooring installations.

Usage

When hard tile flooring is installed the pieces are placed into the adhesive backing with gaps between them, so that they will not cause cracking if the materials expand or contract against one another during summer and winter temperature shifts. These gaps leave vulnerable lines that could allow moisture and germs to penetrate down past the surface covering to the sub floor.

Grout is used to seal the lines between tiles with a material that is resilient enough to withstand most stains, and yet is yielding enough to buffer the expansion and contraction of floor tile materials over time. The process creates a floor that is solid, sealed, secured, and even adhered further to the floor and itself as a structure through the use of intersecting grout lines.