Mixing mortar

Mixing mortar
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Mixing of the ingredients is usually done in a mechanical concrete mixer.

The dry ingredients are placed in a drum and mixed to a uniform colour.
Water is finally added and mixing continues to give a uniform
consistency. Mortar should never be remixed, nor should old mortar be introduced into a fresh banker.Old mortar should not be ‘freshened up’
or ‘knocked up’ by adding more water.Once the water is added to the banker
of ingredients,the chemical reaction of ‘setting’commences. It takes up to
about 3 hours to reach an ‘initial’ set(or get a skin on). This is the point in which the mortar should no longer be used for building. In practice mortar should be used within two hours of mixing.
To ensure the correct consistency in the mix a gauging box can be used.
This is a four-sided box or bucket which is filled with sand or cement,instead of roughly from the shovel,thus ensuring that 5 parts sand & 1 part cement(for example) is exactly the same measure for every mix,this way of mixing your mortar will give the same shade for every mix.Mortar can be mixed by hand but only for small job`s. Consistency between bankers is difficult to achieve with hand mixing.Water is added and the whole mixed to an even consistency.

Waterproofers

Water repellants prevent water penetrating
the pore structure provided there is no pressure
behind the water. Modern
water repellants are based on synthetic
resins which coat the pore sides, preventing
water from entering unless under pressure.
Modern
chemistry has given us synthetic resins which
are capable of blocking off the pore structure,
even under considerable pressure, but
be aware that they are not all ‘equal’. For example,
there are waterproofers based on EVA-
ethyl vinyl acetate, available in a liquid &
a powder form. Both are simply added to the
mortar mix in the recommended proportions,
but the liquid form is quickly washed out of
the pore structure whereas the powder form
is more permanent in its effects.

Accelerators

Accelerators are chemicals added to a mortar
to speed up the reaction between the cement
and the water, known as ‘setting’. If a very fast set is required
it is better to use quick-setting Portland
cement.

Frostproofers

Frostproofers are nothing more than accelerators.
Acceleration of the ‘set’ generates more
heat, thus protecting the mix against
frost attack. An accelerated setting time
also means the mortar has a shorter time span
during which it can be frozen.

Rain
Rain makes bricks and blocks unsuitable
for building, the excessive moisture content
leaving mortar in beds and joints so
sloppy that it runs out – particularly the
binder, leaving a weakened mortar behind
and trails of binder down the face of the
wall.
If frost follows rain, then the water in the
mortar & the bricks or blocks may freeze.
Masonry just built should be protected
from penetration by rain. Waterproof covers
should be placed on top of the wall &
weighted down. A good overhang beyond
the face of the wall may be necessary.