Mortar
Mortar is a material used in masonry construction to fill the
gaps between the bricks and blocks used in construction. Mortar is
a mixture of sand, a binder such as cement or lime, and water and
is applied as a paste which then sets hard.
Gypsum mortar
The earliest known mortar was used by the ancient Egyptians
and was made from gypsum. This form was essentially a mixture of
plaster and sand and was quite soft.
Portland cement mortar
Portland cement mortar (often known simply as cement mortar)
is created by mixing Portland cement with sand and water. It was
invented in the mid-19th-century, as part of scientific efforts to
develop stronger mortars than existed at the time. It was
popularised during the late 19th century, and by 1930 it had
superseded lime mortar for new construction. The main reason for
this was that it sets hard and quickly, allowing a faster pace of
construction.
The Portland cement mortar is the basis for concrete, a
mixture usually comprised of this particular mortar with the
addition of gravel.
Lime mortar
Lime mortar is created by mixing sand, slaked lime and
water.
The earliest known use of lime mortar dates to about 4000BC in
Ancient Egypt. Lime mortars have been used throughout the world,
notably in Roman Empire buildings throughout Europe and Africa. The
vast majority of pre-1900 masonry buildings in Europe and Asia are
built from lime mortar.
The process of making lime mortar is simple. Limestone is
burnt in a kiln to form quicklime. The quicklime is then slaked
(mixed with water) to form slaked lime, either in the form of lime
putty or of hydrated lime powder. This is then mixed with sand and
water to form mortar.
This kind of lime mortar, known as non-hydraulic, sets very
slowly through reaction with the carbon dioxide in air. A very
thick wall made of lime mortar may take centuries to completely set
and harden. The speed of set can be increased by using impure
limestones in the kiln, to form a hydraulic lime that will set on
contact with water. Such a lime must be stored as a dry powder.
Alternatively, a pozzolanic material such as calcined clay or brick
dust may be added to the mortar mix. This will have a similar
effect of making the mortar set reasonably quickly by reaction with
the water in the mortar.
On modern construction sites silos of factory produced mortars
have replaced the labourer and concrete mixer 'knocking up' batches
of mortar.
Factory-produced mortars offer:
- Accurate cement content.
- Consistent quality, strength and colour.
- Reduced mixing and labour costs.
- Reduced wastage.
- Compliance with specifications.
- Improved Health and Safety on site.
There are two main types of factory-produced mortar: lime:sand
and ready to use mortar.
Lime:sand
Lime:sand mortars are a blend of sand and lime to which cement
and water is added on site to produce a masonry mortar. These
mortars are well known for their plasticity and workability. The
fact that they can completely fill vertical as well as horizontal
joints helps in achieving good workmanship. The mortar also spreads
easily under the trowel, so increasing productivity and minimising
wastage.
Ready-to-use
Ready-to-use mortars
are made in factories under tightly-controlled conditions and
delivered to site, ready to use. They have guaranteed mix
proportions and overcome any potential problems relating to site
mixing.
Wet
ready-to-use mortars are stored in tubs on
site and require no further mixing. They incorporate a retarding
agent which makes them fully usable for a specific period - usually
some 36 hours.
Dry
ready-to-use mortars are stored in silos or
bags. Silos are delivered to site complete with integral mixers and
requiring only power and water supplies to be
connected.
