Smoothing grout between tiles with a rubber grout float.

Grout is a dense fluid that hardens used to fill gaps or as reinforcement in existing structures.[1] Grout is generally a mixture of water, cement, and sand, and is employed in pressure grouting, embedding rebar in masonry walls, connecting sections of precast 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 water-resistant seal.

Although both grout and its close relative mortar are applied as a thick suspension and harden over time, grout is distinguished[2] by its low viscosity and lack of lime (added to mortar for pliability); grout is thin so it flows readily into gaps, while mortar is thick enough to support not only its own weight, but also that of masonry placed above it.[1]


Grout varieties include tiling, flooring, resin, nonshrinking, structural, and thixotropic grouts.[3] The use of enhancing admixtures increases the quality of cement-based materials and leads to greater uniformity of hardened properties.[4]

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 is produced in sanded and unsanded varieties, which affects the strength, size, and appearance of the grout.[5] The sanded variety contains finely ground silica sand; unsanded is finer and produces a smoother final surface. They are often enhanced with polymers and/or latex.[6]

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.[2] Nonshrinking grout is used beneath metal bearing plates to ensure a consistent bearing surface between the plate and its substrate, which adds stability and allows for higher load transfers.[7]

Portland cement is the most common cementing agent in grout, but thermoset polymer matrix grouts based on thermosets such as urethanes and epoxies are also popular.[8]

Portland cement-based grouts include different varieties depending on the particle size of the ground clinker used to make the cement, with a standard size around 15 microns, microfine from 6–10 microns, and ultrafine below 5 microns. Finer particle sizes let the grout penetrate more deeply into a fissure. Because these grouts depend on the presence of sand for their basic strength, they are often somewhat gritty when finally cured and hardened.

From the different types of grout, a suitable one has to be chosen depending on the load. For example, a load up to 7.5 tons can be expected for a garage access [two-component pavement joint mortar (traffic load)], whereas a cobbled garden path is only designed for a pedestrian load [one-component pavement joint mortar (pedestrian load)]. Furthermore, various substructures determine whether the type of grout should be permanently permeable to water or waterproof, for example, by concrete subfloor.

This section needs expansion with: Expanding grout. You can help by adding to it. (May 2023)

Tools and treatments

Tools associated with groutwork include:

See also


  1. ^ a b "Not mortar, not concrete—grout!". Masonry Advisory Council. 28 April 2015. Archived from the original on 2015-09-07. Retrieved 2015-09-13.
  2. ^ a b Beall, Christine (1987). Masonry Design and Detailing for Architects, Engineers and Builders. McGraw-Hill. p. 103. ISBN 978-0-07-004223-0.
  3. ^ "Types of Grout: Picking the Right Grout for Your Project". Home Reference. 2019. Retrieved 2021-03-31.
  4. ^ "Influence of thixotropy on stability characteristics of cement grout and concrete". Research Gate. 2002. Retrieved 2021-03-31.
  5. ^ "Selecting and Specifying Mortar and Grout for Unit Masonry" (PDF). Portland Cement Association. 1998. Retrieved 2021-03-31.
  6. ^ "Polymer Thinsets and Grout". FCI Mag. 2002-01-23. Retrieved 2021-03-31.
  7. ^ "Grout or General Purpose Non Shrink Grout". Retrieved 2021-03-31.
  8. ^ a b DM Harrison, The Grouting Handbook, A Step-by-Step Guide for Foundation Design and Machinery Installation, Elsevier Press, 2013, ISBN 978-0-12-416585-4