Page 117 - Masonry and Concrete

Understanding Masonry
116 CHAPTER FOUR

The type of lime used in building is a burned lime made from sed-
imentary limestone. Powdered hydrated lime is used today instead of
lime putty. Only lime that is labeled “mason’s lime” is suitable for
masonry work. Lime adds plasticity to mortar, so it spreads easily into
tiny surface indentations, pores, and irregularities in the units and
develops a strong physical bond. Lime also improves water retention.
Mortar with lime holds its moisture longer, resisting the suction of dry,
porous units so that enough water is maintained for proper curing and
cement hydration. Lime is packaged in bags containing exactly one
cubic foot of material and weighing exactly 40 lbs. This packaging
allows consistency in proportioning and mixing mortar and grout by
either weight or volume measurement.

Masonry Cements and Mortar Cements: Masonry cements are pro-
prietary mixes of cement with chemical or mineral additives. Masonry
cements do not necessarily contain portland cement and hydrated
lime, but may include combinations of portland cement, blended
cements, plasticizers, and air-entraining additives. Finely ground
limestone, clay, and lime hydrate are often used as plasticizers
because of their ability to adsorb water and thus improve workability.
Masonry cements are popular for residential construction because of
their convenience and good workability. Since masonry cements have
all the cementitious ingredients preblended and proportioned in a sin-
gle bag, they are easier to mix on site. For small projects, masonry
cements are more convenient because all that is required is the addi-
tion of sand and water. Masonry cements are manufactured as Type M,
Type S, and Type N, to correspond with the mortar type in which they
are intended to be used.
Like all proprietary products, different brands of masonry cements
will be of different quality. Because of the latitude permitted for ingre-
dients and proportioning, the properties of a particular masonry
cement cannot be accurately predicted on the basis of compliance
with industry standards. They must be established through perfor-
mance records and laboratory tests. Some building codes do not per-
mit the use of masonry cements in highly active seismic areas. In
addition to mortars made from portland and lime or from masonry
cement, some building codes include mortars made from mortar
cement. Generally, proprietary masonry cements that can produce

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