Lime ~ traditional mortars are a combination of lime, sand and
water. These mixes are very workable and have sufficient flexibility
to accommodate a limited amount of wall movement due to
settlement, expansion and contraction. The long term durability of
limemortarsispoorastheycanbreakdowninthepresenceof
atmospheric contaminants and surface growths. Nevertheless, lime is
frequently specified as a supplementary binder with cement, to
increase mix workability and to reduce the possibility of joint
shrinkage and cracking, a characteristic of stronger cement mortars.
Cement ~ the history of cement type mortar products is extensive.
Examples dating back to the Mesopotamians and the Egyptians are
not unusual; one of the earliest examples from over 10000 years
ago has been found in Galilee, Israel. Modern mortars are made with
Portland cement, the name attributed to a bricklayer named Joseph
Aspdin. In 1824 he patented his improved hydraulic lime product as
Portland cement, as it resembled Portland stone in appearance. It was
not until the 1920s that Portland cement, as we now know it, was
first produced commercially by mixing a slurry of clay (silica, alumina
and iron-oxides) with limestone (calcium carbonate). The mix is burnt
in a furnace (calcinated) and the resulting clinker crushed and bagged.Mortar ~ mixes for masonry should have the following properties:
* Adequate strength
* Workability
* Water retention during laying
* Plasticity during application
* Adhesion or bond
* Durability
* Good appearance ~ texture and colourModern mortars are a combination of cement, lime and sand plus
water. Liquid plasticisers exist as a substitute for lime, to improve
workability and to provide some resistance to frost when used
during winter.
Masonry cement ~ these proprietary cements generally contain
about 75% Portland cement and about 25% of fine limestone filler
with an air entraining plasticiser. Allowance must be made when
specifying the mortar constituents to allow for the reduced cement
content. These cements are not suitable for concrete.
Refs. BS 6463-101, 102 and 103: Quicklime, hydrated lime and
natural calcium carbonate.
BS EN 197-1: Cement. Composition, specifications and
conformity criteria for common cements.Mortars for Brickwork and Blockwork (1)