50-54 CONCRETE POOLS:SPN Master pages 20/11/2009 10:18 Page 54
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Spray-applied concrete, “shotcrete” is
separated into either a wet process or a
dry process. For a dry-mix process, dry
cement and aggregate are driven through
an applicator hose, with water only added
at the nozzle. A wet-mix process is where
the concrete is pre-mixed before being
loaded into a hopper, from which it is
pumped through the delivery hose and
spray-applied with compressed air added
at the nozzle via a separate hose.
Spray-applied concrete technology has
been in use for about 70 years, primarily
in civil engineering applications, such as
roads, roadway repairs and tunnels, and
in commercial projects. The most
common residential uses are swimming
pools and foundation repair. More rarely,
it is used for basement foundations.
The finished strength of spray-applied
concrete averages 5,500psi. The resultant
As well as versatility of shapes, shotcrete lends itself to integrated design
concrete is different from conventional
because steps and spas can be ‘shot’ at the same time as the pool cast-in-place concrete with regard to the
application surface, reinforcing, and of
course method of application. The wet
shell ready for finishing (after a curing labour-intensive and less expensive than process is often the method of choice for
period). The sprayed concrete process can pouring concrete. high-strength applications.
be completed in up to 50% of the time of Like all concrete structures, these pools As with conventional poured concrete,
the traditional shuttered and poured can last decades when properly constructed. properties of spray-applied concrete can
method reducing labour costs and Improperly constructed, however, they can be altered and enhanced through the
considerably speeding up construction crack from ground movement caused by addition of additives or admixtures, such
time, this is especially useful in basement freeze/thaw cycles, high water tables, hillside as silica fume, air-entraining admixtures,
construction. locations or seismic activity. The cost goes fibres and accelerators. Accelerators are
Shotcrete, is accepted by all specialist up in areas with these conditions because often incorporated at the plant so the
companies by definition, to offer a extra reinforcing is needed to prevent concrete sets quickly after application.
freedom of design necessary to build pools movement. Because these pools are Spray-applied concrete is a versatile
to suit just about anyone. It also lends constructed entirely on the site, the quality technology. Besides walls and swimming
itself the most popular designs in new depends on the job’s craftspeople. pools, it can be used to create floors,
pools – vanishing edges. Concrete construction takes the longest roofs, and curved or other complex and
Beneath the concrete is a cage of because the entire product is created on site variable surfaces. Spray-applied concrete
reinforcing rods. That produces an extremely from basic materials such as concrete, steel may be applied to wood, steel, polystyrene
strong wall and floor. “A shotcrete pool has rebar and plumbing. A basic pool or any other surface to which it will adhere
tremendous structural integrity (rectangular, no waterfeatures) on a property long enough for the concrete to set. spn
“We can do anything with shotcrete.” with an existing home can be built in four to
The possibilities, he adds, are limited only six weeks, depending on the region.
FURTHER INFORMATION
by someone’s imagination. This timeline also assumes there is no
GUNCAST
( 01428 707944
“We’ve done pools using the most interruption, everyone is immediately
: www.guncast.com
demanding shapes. Some designs have available and there are no scheduling,
GUNITE GROUP
been stunning and wonderful.” delivery, weather glitches or change orders
( 01480 466880
In addition to versatility of shapes, – meaning clients change their minds
: www.gunite.co.uk
shotcrete lends itself to integrated design about something or decide to add on
PREMIER GUNITE
( 01483 235988
because steps and spas can be ‘shot’ at something extra. : www.premiergunite.co.uk
the same time the pool is being ‘shot’. Spray-applied concrete has been in use SPRAYED CONCRETE SERVICES
That’s important for an overall seamless for almost a century, especially in
( 01704 533999
: www.sprayedconcreteservices.co.uk
finished product. swimming pool construction.
One architect admitted that his company
has “never done the same shape twice”.
New composite materials made of
“LIKE ALL CONCRETE STRUCTURES,
smooth pebbles and sprayed concrete
make beautiful, natural-looking surfaces
THESE POOLS CAN LAST DECADES
that are very forgiving and extremely
durable and maintenance-free.
WHEN PROPERLY CONSTRUCTED.
Pneumatically applying concrete was not
the first method used to create a concrete
IMPROPERLY CONSTRUCTED, HOWEVER,
shell. Originally, concrete pools were made
of poured concrete, meaning workers
THEY CAN CRACK FROM GROUND
create a set of forms and pour the
concrete into the forms to hold it into
MOVEMENT CAUSED BY FREEZE/THAW
vertical walls. Shotcreting and guniting
became the most common methods of
CYCLES, HIGH WATER TABLES, HILLSIDE
concrete construction because they don’t
require forms, making it quicker, less
LOCATIONS OR SEISMIC ACTIVITY”
54 Swimming Pool News December 09 Digital edition available at www.swimmingpoolnews.co.uk
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