Cement rendering is the application of a thin premixed surface of
sand, cement

Cement

In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

 and lime plaster

Lime plaster

Lime plaster is type of plaster composed of hydrated lime, sand and water. Lime plaster is similar to Lime mortar, the main difference is the based on use rather than composition. Traditional lime plaster contains also horse hair to reinforce plaster....

 to brick, cement, stone or mud brick. It is
often textured, coloured or painted after application. It is
generally used on exterior walls but can be used to feature an
interior wall.

Depending on the 'look' required, rendering can be fine or coarse,
textured or smooth, natural or coloured, pigmented or painted.

The cement rendering of brick, concrete and mud houses has been used for
centuries to improve the appearance (and sometimes weather
resistance) of exterior walls. It can be seen in different forms all
over southern Europe. Different countries have their own style and
traditional colours.

Finishes

Different finishes can be created by using different tools such as trowels ,
sponges, or brushes. The art in traditional rendering is, (apart
from getting the mix right), the appearance of the top coat.
Different tradesmen will have different finishing styles and be able
to produce different textures and decorative effects. Some of these
special finishing effects may need to be created from a thin
finishing 'top coat' or from a finishing wash.

Acrylic rendering

There are also a wide variety of premixed renders for different situations.
Some have a polymer additive to the traditional cement, lime and sand mix
for enhanced water resistance, flexibility and adhesion.

Acrylic premixed renders have superior water resistance and
strength. They can be used on a wider variety of surfaces, including
concrete, cement blocks, and AAC concrete panelling. With the right
preparation, they can be used on smoother surfaces like cement sheeting,
new high tech polymer exterior cladding such as
Uni-Base, and expanded Polystyrene. A few of these require activation
with cement just prior to application.

Some of these premixed acrylic renders have a smoother complexion than
traditional renders. Others can even be spayed on.

There are also a wide variety of acrylic bound pigmented 'designer'
finishing coats that can be applied over acrylic render. Depending
upon the product, they can be rolled, trowelled or sponged on. A
limited number can also be spayed on. Various finishes, patterns and
textures are possible such as sand, sandstone, marble, stone, stone
chip, lime wash or clay like finishes. There are stipple, glistening
finishes, and those with enhanced water resistance and anti fungal
properties. Acrylic renders take only 2 days to dry and cure - much
faster than the 28 days for traditional render.

Traditional rendering

To ensure adhesion, the surface to be rendered is initially hosed off to ensure
it is free of any dirt and loose particles. Old paint or old render
is scraped away. The surface is roughened to improve adhesion. For large
areas vertical battens are fixed to the wall
every 1 to 1.5 metres, to keep the render flat and even.

Cement render consists of 6 parts clean sharp fine sand, 1 part cement and 1
part lime. The lime makes the render more workable and reduces
cracking when the render dries. Any general purpose cement can be
used. various additives can be added to the mix for increasing adhesion.
Coarser sand is used as the base layer and slightly finer sand for the top
layer.