Surface Finishes on Concrete

Concrete can be given many different surface finishes including:
BROOMING
COLOURING
PATTERNING or
POLISHING
A coloured or patterned surface finish can make
concrete look more attractive and interesting.
CONCRETE In order to minimise problems arising when using any form of coloured
concrete for domestic paving, either a minimum grade of 25 MPa or concrete containing
not less than 280 kg of cement/m3 should be used. Other forms of decorative concrete,
or in commercial work, will normally require a higher grade of concrete.
TEST PANELS To find out how a colour or pattern will look always do a small test area
before beginning the bulk of the work.
CURING COLOURED CONCRETE Curing is the most important step in colouring
concrete. The concrete surface must stay evenly moist or the colour will be uneven. Poorly
cured concrete can even affect a painted concrete surface.
See CHAPTER 10 Curing Concrete
COLOURED FINISHES There are four ways to colour concrete.
The Dry-Shake Method The dry-shake method
uses a mixture of a mineral oxide pigment (or
colour), cement and specially graded fine
aggregates. The colour is added when
compaction, screeding and bleeding has
finished, as part of finishing. Uniform reliable
results are best achieved if the concrete is
supplied pre-mixed by the supplier using weight
batched dry components.
Shake 2/3 of the dry material onto the concrete
surface, spreading it evenly with a float. Leave
for a minute or so to soak up some moisture.



Shake the last 1/3 of the dry material onto the
concrete at right angles to the first application
and again after it has dampened up, spread
evenly with a float. The two applications help to
give a more uniform colour and thickness.
Re-tool any edges and joints.
See CHAPTER 11 Joints in Concrete
After a while the surface must be re-floated.



FULL DEPTH COLOUR The colour is added to the concrete
during mixing so all the concrete is coloured, then the concrete
is compacted and finished as for normal concrete.
The colour pigment additives should generally be in the range
of 3–7% by weight of the cement. Higher quantities may affect
the strength and durability of the concrete. Check
manufacturer details for colour selection.
See CHAPTER 2 Properties of Concrete


Each batch must be accurately proportioned, thoroughly mixed and well floated
to give an even colour.
See CHAPTER 9 Finishing Concrete
The colour of the cement powder may effect the shade of the final colour,
ie a dark grey cement may affect light colours.
APPLIED FINISHES Applied finishes, including paints, tinted
sealers and trowelled-on coatings provide a wide range of
colours and are easily applied to hardened dry concrete.
Paint finishes are either water-based or solvent
based. They will wear easily and will need to be
reapplied periodically.
CHEMICAL STAINS A chemical stain soaks into the
concrete surface and colours its, only wearing away
as much as the surface does.
There is only a limited colour
range in concrete stains.


STAMPED PATTERN FINISH A number
of DIFFERENT PATTERNS can be stamped
into the surface of setting concrete. This
includes cobblestone, slate, tile, brick tile
and timber finishes.
The concrete is placed and compacted
normally, and floated once. A dry shake
colour may also be used.
The patter stamps or pads/mats are then placed carefully on the concrete surface. When
mats are used a release agent will be needed to allow the mat to be removed. At least two
moulds are needed to step from one to another giving continuous and matching patter.
Step onto the moulds, pressing them into the concrete surface to the desired depth; up to
6–10 mm for cobblestones and less for other patterns. Deep patterns may be a hazard for
pedestrians.
When using pads the grooves may be rounded by laying a sheet of plastic across the
concrete surface before stamping. The surface must then be broomed to give a non-slip
finish. Use small handstamps for the edges and any difficult to reach areas.
Brick, or tile finishes, (stencilled concrete) can be obtained by floating a paper template
into the concrete surface before applying a dry shake. The template forms the mortar lines.
EXPOSED AGGREGATE FINISH An exposed aggregate finish can be an attractive
decorative finish. Different sizes and colours of aggregates allow many different looks.
The concrete can be made as normal, and the course aggregate exposed. This is done by
waiting until the surface is firm, but not dry, then brush, wash or broom away any cement
paste until the aggregates are exposed. Then cure the concrete.
A surface retardant can be used to aid the process.
Alternatively, there are two ways to get an exposed aggregate finish by adding special
aggregates to the surface.
Method A
Place, compact and level the concrete to about 10 mm below the top of the forms.
Spread selected aggregates over the concrete in a layer and press them into the concrete
until completely covered.



Method B
Place, compact and level concrete to about 5 mm below the top of the forms.
Mix a 'Topping Coat' – A mix of aggregates and cement paste in the ratio 2:1.
Use only enough water to make the coat workable.
See CHAPTER 2 Concrete Properties
Spread the topping over the concrete, level,
tamp down and finish with a trowel.
FOR BOTH METHODS leave the concrete until the cement paste on the surface is firm,
but not dry, then brush or with a fine mist spray wash away some of the cement paste
covering the aggregates.
In both cases extra cleaning can be done with a dilute solution of hydrochloric acid.
The solution should be 1 part acid to 20 parts water.Wet the concrete first and rinse off
thoroughly afterwards. Observe safety procedures.
See CHAPTER 15 Removing Stains from Concrete
To see what an aggregate finish will look like, do a test area first.
Different colours of cement can be used to get a better effect. For instance a white or
off-white cement may be used with a light stone where a grey cement may create a clash
of colours.
A BROOMED FINISH To give a skid-resistance surface a stiff, or soft, bristle broom can
simply be drawn across the surface of concrete. The broom can be drawn in straight or 's'
shape lines.
POLISHED CONCRETE Polished concrete is a finish used on the interior and exterior of
dwellings. A variety of finishes can be achieved by using different techniques or products.
The different finishes can be achieved by using liquid polishes, latex coatings, chemical
sealers, grinding to expose the aggregates, colours, stains and special aggregates to
achieve other desired effects.
For further details please refer to Polished Concrete Floors – Briefing 05.