grout grout or grout grout (occasionally known as grout borad in Spain) or with the anglicism grout, is a dense fluid that hardens when applied and is used in construction, to fill gaps or as reinforcement in existing structures. It is generally a mixture of water and cement that may also contain very fine sand or other substances that increase resistance and prevent shrinkage when drying. It is commonly used in masonry walls, connecting precast concrete sections, filling gaps, and sealing joints such as those between tiles.[1] Common uses for grout in the home include filling shower floor tiles and kitchen tiles. Unlike other structural pastes such as plaster, properly mixed and applied grout forms a water-resistant seal.[2]​.

Originally, grouting grouts were prepared by mixing water with cement, which could be white or gray, depending on the type of tiling or flooring to be grouted. In cases where for some reason, generally aesthetic, the space between tiles was several millimeters wide, a small amount of fine sand was added to the grout, always in proportions less than the weight corresponding to the cement, very far from the proportions corresponding to the mortar. [3]​This type of grout, called cementitious grout, is still one of the most popular types of grout, due to its versatility, resistance and durability and is currently marketed with a wide variety of colors to match the appearance of the tile[4]​and with different enhancing additives that improve its characteristics and allow for greater uniformity of the hardened properties.[5]​The sanded variety contains finely ground silica sand; The unsanded variety is finer and produces a smoother final surface. Their characteristics are often improved with polymers and/or latex.

In addition to grouts for grouting tiles, grouts, almost always cementitious, are also used for[6]​.

The slurry is prepared in a similar way to how traditional cement paste is prepared, except that in the case of slurries the proportion of water is higher and the proportion of sand is either not included or is proportionally very low. Mixing is done with a mortar or a good manual mixer, which ensures quality and homogeneity. Larger concrete mixers do not generate shear within the material, which does not ensure a homogeneous mix. Mixing with a concrete mixer requires more water and therefore lowers the strength of the material.