Mortar is the most fundamental material used in bricklaying. Depending on
your point of view, mortar is used to stick the bricks together or to keep them apart.
Mortar has been a necessary part of masonry construction since time
immemorial. The mortar makes walls wind proof, waterproof, ties the units
together and makes the walls stronger.
Mortar consists of three things:
- a cementious binder; cement and/or lime,
- a filler, usually sand: and
To produce a mortar that will comply with the Masonry Standard the ingredients should be properly batched, that is , measured using a bucket or box made for the job.
A. Bucket Batching . A bucket can be used to count out the required volume of cement. lime and sand. This method is only suitable for small volumes of material, but it is accurate and will remove the risk of the brickwork needing to be demolished because the mortar is too weak. The ingredients should be placed in the bucket until they are flush with the top, or be overfilled and then the excess struck-off.
B. Gauge-box Batching . With this technique the
ingredients are measured out on a good level
surface and then transferred to the mixer. For the
typical 2 or 3 cubic foot mixer a wooden box is
constructed without a top or bottom. This is filled with
sand, any excess is struck-off and then the box is lifted
clear to leave the sand which can be shovelled into the
mixer, A bucket is then used to gauge the required
amounts of cement and lime; see Gauging the Cement
and Lime Content below.
Originally, clay was used to mortar the sun dried bricks together. As firing
the clay units became the method of production, lime took over as the
principal cementitious binder.
Water has always been necessary to make first the clay, then lime
mortar, and now cement mortar plastic and suitable for laying bricks in
Today, mortar for bricklaying can contain several ingredients and sometimes additives. The following list will itemise them and their intended use in mortar.
Portland cement as we know it today, was invented by Joseph Aspdin, a bricklayer in 1824. It changed the way buildings were constructed as it produced a much stonger mortar than had been available proir or to this time. Most mortars and all concretes rely on Portland cement for their strength today.
General Purpose Cement 100% Portland cement
Contains no additives or fillers and produces the best results.
Was known as Type A.
In 1824, Joseph Aspdin, a Hunslet Leeds bricklayer, was granted patent number 5022 for a cement he discovered after he mixed a calcined hard limestone with clay, ground it down, mixed it into a slurry, and then burned the mixture a second time. Aspdin called his product "Portland" cement because the mortar made from the cement resembled in color a widely used building stone quarried on the Isle of Portland off the coast of England (Lesley 1924).
Manufacturing Portland Cement
The manufacturing of portland cement is similar to that of lime in that the process requires the heating of raw materials through a kiln. The earliest kilns in which cement was burned in batches were called bottle kilns, followed by chamber kilns, and then shaft kilns. The shaft kiln is still used in some countries, but the dominant means of burning cement today is continuous rotary kilns. These kilns, up to 660 feet long and 20 feet in diameter, are made of steel and lined with firebrick.
General Builders Cement
Portland cement with blended fly ash and blast furnace slag. This cement manufactured for mortar and concrete. The additives can cause problems during brickcleaning.
Off white cement is manufactured to produce an off white mortar.
For ordinary mortar it is recommended that general purpose be used. The
cement will soften and break down more consistently when the brickwork is being acid cleaned.
The strength of the mortar can be accurately gauged where the proportions
are properly batched. The general purpose cement may also assist in
producing a serviceable mortar where ingredients are shovel batched.