Grout is a construction material used to embed rebars in masonry walls, connect sections of pre-cast concrete, fill voids, and seal joints (like those between tiles). Grout is generally a mixture of water, cement, sand, often color tint, and sometimes fine gravel (if it is being used to fill the cores of concrete blocks). It is applied as a thick emulsion and hardens over time, much like its close relative mortar. Unlike other structural pastes such as plaster or joint compound, grout, when mixed and applied correctly, creates a waterproof seal.
Structural grout is often used in reinforced masonry to fill voids in masonry housing reinforcing steel, securing the steel in place and bonding it to the masonry. Non-shrink grout is used beneath metal bearing plates to ensure a consistent bearing surface between the plate and its substrate.
Portland cement-based grouts come in different varieties depending on the particle size of the ground clinker used to make the cement, with a standard size of around 15 microns, microfine at around 6-10 microns, and ultrafine below 5 microns, with the ability of the final grout to penetrate a fissure largely dependent on this particle size (smaller size equates to greater penetration). Because these grouts depend on the presence of sand for their basic strength, they are often somewhat gritty when finally cured and hardened.
Tiling grout is often used to fill the spaces between tiles or mosaics, and to secure tile to its base. Although ungrouted mosaics do exist, most have grout between the tesserae. Tiling grout is also cement-based, and comes in sanded as well as unsanded varieties. The sanded variety contains finely ground silica sand; unsanded is finer and produces a non-gritty final surface. They are often enhanced with polymers and/ or latex.
There are several tools associated with applying and removal of grout such as: