Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to surface treatments for
rigid structures and may be especially applicable although
not limited to structures such as swimming pools of reinforced
concrete and other rigid structures requiring the application
of a durable surface finish to a relatively large area.
More particularly the present invention is concerned
with a surface finish being of the type known as an "exposed
aggregate", which usually comprises relatively small solid
particles such as selected gravel bound together and to the
substrate by a suitable cement binder.
One known manner of forming an exposed aggregate surface
finish for a concrete structure such as a path or swimming
pool is to allow the concrete structure to cure and subsequently
to apply cement in the form of an epoxy adhesive to the
substrate and to trowel on the aggregate. The aggregate may
be fine particles of gravel, for example coloured river
gravel having a size of the order of one-eighth inch diameter.
Another known method is to pour the concrete structure
and before the concrete hardens to apply a thin layer of
aggregate to the surface of the concrete by a seeding technique.
The gravel is then worked with a trowel so as to become
partially embedded in the concrete. This technique permits
a far more durable and permanent finish which is highly
resistant to light, water, and the pressure of foot or vehicle
traffic. By contrast an epoxy-aggregate system has more
limited binding power of the aggregate and the epoxy resin
may degrade after a substantial period of exposure to strong
sunlight whereby the aggregate may become detached.
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It is also po~3ible to provide an exposed aggregate
finish by using a portland ~ype cement and aggregate mixture
applied as a surface layer to a concrete substrate, the
excess cement being removed by a washing technique to leave
partially exposed a multiplicity of particles of aggregate.
However, this system, which can include use of a chemical
retarding agent to delay curing of the cement near the
surface, is highly time consuming and requires great patience
and the use of skilled operatives. Accordingly this method
is expensive and a small team can only compIete a small area
in one day. Thus, a large job requires joints between
separate sections.
The present invention, broadly speaking, is concerned
in one aspect with a method of applying a surface coating
which includes a selected aggregate, particles of which are
to be exposed to provide the desired surface finish, the
method comprising forming a mix comprising selected aggregate
and portland-type cement, the mix being richer in cement
than the ratio of three parts by volume aggregate to one
part by volume of cement, adding water in a controlled
quantity whereby the batch has a slump which is small compared
with a slump of six inches, the aggregate being an aggregate
which will pass through a mesh substantially smaller than a
half inch mesh and the mix containing substantially no
fines, supplying the mix to a pumping apparatus and operating
the pump to discharge the mix through a discharge nozzle to
deposit a layer on a rigid substrate such as concrete,
applying localized pressure progressively over the surface
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of the coating layer for the purpose of working the deposited
mix to pack the agyregate particles together and tending to
draw the portland cement to the surface of the layer, and
applying a fine water spray to wash away excess portland
cement.
Preferably the method of the invention is additionally
characterized by one or more of the following features:
(1) The aggregate will pass through a mesh of about one-
eighth inch, the particles being approximately uniform
in size and for example being washed river gravel of a
rounded form and of selected colours.
(2) The mix is very rich in cement, for example of the
order of 1:1 by volume.
(3) The slump of the mix is very small, for example of the
order of one inch using a standard slump test, the
slump being preferably particularly small where a
vertical surface is to be coated with the exposed
aggregate finish.
(4) The pumping apparatus may be a conventional mortar or
plaster pumping apparatus suitably adapted if necessary,
the apparatus being for example of the type used to
spray plaster ceilings in buildings.
(5) Calcium stearate is used in the mix to improve the
workability thereof.
The invention in another aspect extends to a structure
such as a concrete swimming pool having a surface coating
thereon formed according to the method in any one of the
above described forms. However, the invention may also be
applied to the provision of an exposed aggregate finish on
other large surface areas such as walkways, driveways and
even vertical facings on buildings.
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The present invention may have many advan-tages which
will be more particularly described with reference to the
application of the invention to a surface coating for swimming
pools.
Although an exposed aggregate finish could be applied
to the interior of reinforced concrete swimming pools by
known methods, this is very rare and is partially due to
the high cost of conventlonal techniques compared with
alternative surface finishes but also due to the problem of
coating the large surface areas; generally several days work
for a typical group of tradesmen would be required thereby
necessitating the provision of many joints which would be
undesirable.
Use of the invention in at least a preferred embodiment
can permit the following principal advantages to be obtained:
(1) The exposed aggregate finish can be applied on the same
day as the concrete swimming pool is poured. Normally
formwork is erected to define the exterior of the
swimming pool or alternatively the walls of the hole in
the ground are utilized; the reinforcing steel is
- placed in position and the concrete pumped to buildup
the wall around the swimming pool progressively, the
slump of the concrete being relatively low so that hand
trowelling can continually occur on the interior of the
swimming pool to provide a smooth surface finish. As
soon as this operation has been completed, the exposed
aggregate mix can be pumped and trowelled into position.
(2) In general the public authorities insist on inspections
including that of safety fences before a swimming pool
is filled. An exposed aggregate finish applied according
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to an embodiment of the invention can safely be left
exposed to the air after application and the swimming
pool can be filled at any desired later date. By
contrast a common surface finish of the interior of a
swimming pool is a powdered marble finish bound in a
plaster which is hand trowelled into position by a
skilled tradesman. As soon as this operation is finished
the swimming pool must be filled to keep the plaster
wet during the critical and slow curing process.
Otherwise excess shrinking of the plaster will occur
thereby leaving unsightly cracks in the plaster finish.
If desired however, swimming pools having an interior
finish applied by a method embodying the invention
could be filled as soon as surface hardening of the
aggregate has occurred although it would in general be
desirable to leave filling the swimming pool for a
period of time such as seven days to permit the reinforced
concrete component to gain structural strength.
(3) Where the exposed aggregate is applied immediately
after surface hardening of the reinforced concrete has
occurred, due to the very rich nature of the surface
coating, faster curing occurs in this surface coating
and this in itself provides a barrier which effectively
retards what would otherwise be a tendency for the
reinforced concrete to cure too quickly and perhaps
crack, this danger being especially great in hot and
sunny weather. Thus, the exposed aggregate can obviate
the conventional practice of keeping a newly poured
reinforced concrete structure damp for a period of
approximately one week.
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(4) The present invention in preferred embodiments lends
itself to efficient, fast and effective methods of
coating concrete requiring only small amounts of labour
yet permitting a durable and permanent finish to be
provided. An efficient pump may be employed to apply
quickly and accurately the desirable coating layer and
after the hand trowelling operation a wide fine water
spray head may be employed to wash down gently but
efficiently remove excess cement.
(5) Another advantage is that exposed aggregate can have a
substantial heating effect on the temperature of the
water by causing heat from the sun to be absorbed; by
contrast commonly adopted plaster-type finishes are
highly reflectant of the heat from the sun's rays and
- the expense of a solar heater ~or raising the temperature
can be obviated.
(6) The exposed aggregate finish can obviate staining and
discolouration which can occur with popular finishes
for swimming pools. Furthermore the problems that can
be associated with tiled swimming pools can be avoided
in that there is no possibility of loosening of tiles.
.
For illustrative purposes only, the invention will be
exemplified with reference to a preferred embodiment described
hereinafter with reference to the accompanying drawings of
which:
Figure 1 illustrates schematically the interior of a
swimming pool being surface coated according to an embodiment
of the invention; and
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I'i~ure 2 is a cros~ ~ec~iollal view on cnlaL~e~ scalc
through the wall of the swimming pool having surL~ce coating
on the interior thereof.
~g tllustrat~d ~n Fiyure 1, ll~e swi~niny ~>ool comlris
a floor 1, an end wall 2 and a side wall 3 of reinforced
concrete, a peripheral deck 4 being integrally formed therewith.
The swimming pool in this embodiment is formed in an excavated
hole in the ground having walls 5, the profile of which acts
as formwork for the concrete. Although only shown in Figure
2, reinforcing steél 11 is positioned in the wall area and
the appropriate mix 12 placed and trowelled in position to
form the walls and deck.
Figure 1 illustrates the formation of an exposed aggregate
coating layer 13 on the interior of the swimming pool, end
wall 2 and part of side wall 3 having the coating thereon.
The surface coating 13 is supplied by a pump 6
(schematically shown) having a hopper 7 into which the
appropriate batch from a mixer is applied, the pump passing
the mixture through a conduit 8 of approximately two inches
diameter to a wide spraying or dispensing head 9 which is
controlled by hand by an operator. The thin surface coating
is built up over the wall surface and when the cement in the
mixture starts to harden, an operator works the surface
coating with a trowel and as the setting action starts to
occur a very fine water spray is applied from a spray head
10 which is connected to a water hose 1~ to remove the
excess cement.
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Pigure 2 illustrates a typical wall cross-section and
shows reinforcing steel 11 in the cen-tre of a reinforced
concrete wall 12 typically of four inches thickness and
having a thin layer 13 typically quarter inch thick on the
interior side, this layer 13 comprising exposed aggregate
which preferably is formula-ted as follows:
Aggregate: One-eignth inch diameter washed
rounded river gravel free of fines.
Mixture: Portland cement one part by volume
to aggregate one part by volume.
Slump: One inch slump.
Additive: Calcium stearate.
A swimming pool may be efficiently built if desired in
a very short period of time such as one working day. A
typical procedure would be as follows:
(a) using suitable digging equipment such as a backhoe and/
or bulldozer, a hole is dug in the ground. This may
take approximately four hours.
(b) Reinforcing steel is placed in position around the
pool, desirably using preprepared panels of welded
mesh.
(c) Concrete of appropriate formulation is pumped to form
the walls, the walls of the hole acting as formwork
and the interior surfaces of the walls being trowelled
by hand.
(d) The exposed aggregate treatm~nt is applied by pumping
the appropriate mixture and trowelling into position
for example by using an ESSEX (trade mark) brand plas-
ter pump. Water washing is conducted as the setting
takes place, a pump being utilized to remove the water
and cement
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slurry whi.ch collects at the deep end of the swimming
pool. The trowelliny has a compaction effect and
preferaby at least one further s-tep of trowelling
occurs before a final water wash to remove excess
cement.
(e) After dryiny and surface hardening, a dilute
hydrochloric acid washdown is conducted to remo~e
excess cement.
(f) After erection of any necessary ancillary equipment
such as safety fencing, the swimming pool may be
filled.
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