Grouts and caulks are special sealants used to fill gaps. They are extensively used in the construction industry to join sections of ceramics, concrete, bricks, and to fill voids and seal joints such as those between tiles. Unlike other structural pastes used in the construction industry, grouts and caulks act as a waterproof seal.
The properties of hardened grouts are often similar to those of mortar, but the application properties are quite different. For example, grouts have a lower viscosity so that they flow readily into gaps, while mortars have to have a much higher viscosity to support the weight of masonry placed on top of it.
Grouts and caulks are usually formulated with cheaper ingredients and are often water based. The main ingredients of most grouts/caulks are water, filler, and cement. High filler loading is preferred to reduce the cost of the product. It also imparts enhanced shrinkage and crack resistance. Besides fillers, some grouts, like flooring grouts, also contain large amounts of sand to further lower cost. To give the grout a pleasing appearance and to match the color to the tile coloring pigments are often added. Other ingredients that are sometimes added include:
Rheology modifiers to impart sag and slump resistance
Surfactants and dispersants to aid in cleaning of the grout after application and to reduce the viscosity
Antimicrobial and/or stain resistance additives to prevent discoloration of the grout
Humectants and plasticizers to impart the desired application characteristics
Adhesion promotors to improve bond strength and wetting
Zinc oxide is one example of a generic antimicrobial agent. Other antimicrobial agents include barium metaborate, zinc and sodium omadine, and triclosan, to name only a few. Typical rheology modifiers are treated and untreated silica, clay and cellulosic rheology modifiers. The usual amount of these ingredients is below five weight percent. Typical humectants found in grouts include neopentyl glycol and urea and typical plasticizers are castor oil, glycol phthalates, and benzoates to name only a few. Common adhesion promoters are functionalized silanes and certain acidic compounds. These ingredients are only added if neccessary and then only in small amounts because they are comparatively expensive.