Masonry Magazine August 1989 Page. 15
GROUT
THE THIRD INGREDIENT
JAMES E. AMRHEIN, S.E.
Executive Director
Masonry Institute of America
Reinforced masonry! Reinforced masonry is the only type of masonry that should be built in "earthquake country." Reinforced masonry is made up of four constituents: the masonry unit, either brick or block; mortar which binds the masonry unit together, provides a leveling bed between units and also architectural appearance; grout, which is the ingredient with which this article is concerned; and reinforcing steel.
Grout is a material used in reinforced masonry that is quite misunderstood.
Grout is not mortar and grout is not concrete. It is somewhere in between. For a rapid visual concept of what grout is, let's call it "soupy concrete." Soupy concrete may give the proper connotation and understanding because it is made up of a cement/water combination which is the paste that binds together the aggregate, which may be sand only or sand and gravel. These are the same ingredients that make up concrete: cement, water, sand and gravel. This is even similar to mortar, which is cement, water, sand and, instead of gravel, lime. All these materials harden into a stonelike mass.
The big difference between concrete, mortar and grout is in their plasticity or fluidity in the initial stage. Mortar is relatively stiff, and if a slump test were made it would have a slump of five to eight inches. Concrete is also relatively stiff with a slump varying from two inches to six inches maximum. The slump of concrete is a controlled requirement for it reflects directly to the water/cement ratio of the concrete mix. This is one major point of variance between concrete and grout. Concrete, with a tightly controlled water/cement ratio, has a relatively low slump, relatively slight plasticity and very low fluidity, for all the water in the concrete will stay within the concrete for it is placed in water-tight forms. All the water in the concrete mix is part of the calculation of the water/cement ratio. Also, in concrete, the forms are spread relatively far apart, and the size of member is relatively large compared to the aggregate material, which allows for easy placement.
Mortar is a plastic material with a low water/cement ratio and high in cement content. Mortar must be relatively stiff in order to be handled on a trowel, to be spread on the masonry unit and to evenly support the masonry units placed on it. This stiffness is required for the masonry wall to be