DURABLE
& ECONOMICAL POOLS
Constructing a pool is inevitably a rather difficult and time consuming
task and it is obviously desirable that the result of this work should
last as long as possible. Pools will improve with age and can give pleasure
for generations provided they are constructed properly and with durable
materials
Portland cement based materials are among the most durable available,
even the crude early types of this cement used by the Romans 2000 years
ago, still survive to this day, no other man made material has such
a pedigree. Wet conditions, such as in pools, are an ideal environment
for Portland cement based materials that actually harden by reacting
with water
Of course, as with all materials, they have their limitations and problems
can arise and the pool then becomes a source of worry rather than of
pleasure These limitations, in particular cracking resulting in leakage
of water, have in the past inhibited the use of concrete pools. All
cement based materials, particularly mortars, are prone to cracking,
quite independently of external stresses, this is made worse when a
high cement content is used, which is essential for an impermeable and
durable material
Over I0 years ago was introduced into the UK special cement reinforcing
fibres, Rein fibres, and a formulation using these fibres for a high
performance mortar, Fibromix. These mortars, with their superior qualities
were found to be particularly beneficial in pool construction overcoming
the problems previously associated with cement based materials and providing
a means of simply and economically constructing very durable pools.
Of course, building a durable pool is far easier where cost is not a
restraint but it is certainly now possible for the DIY pool builder
to economically construct a durable concrete pool which will give pleasure
for generations.
Rein Fibres
Rein fibres are high elastic modulus, synthetic fibres developed and
patented specifically for reinforcing cementitious materials. (there
may be fibres that look the same but, because of the patent, there are
none that are the same) One application of these fibres was to produce
a very high performance mortar, which has proved to be an excellent
material for pool construction. It has been used, over the last decade
very successfully in thousands of pools, both as a waterproof rendering
and to construct the complete pool shell, directly in the ground.
High Performance Mortars.
Fibromlx mortars are waterproof because they enable a high cement content
to be used without the otherwise inevitable problems of cracking. Rein
fibres not only overcome the tendency to self induced cracking, enabling
a higher cement content to be used, but they actually make the resulting
mortar far more resistant to cracking and fracture than conventional
mortar.
Using & Finishing Fibromix Mortars.
Fibromlx mortars are simply produced in the same way as ordinary mortars,
preferably in a small cement mixer as thorough mixing is important,
the Rein fibres being simply added to the mix.
The Fibromix mortar is spread on like a conventional mortar, although
it spreads more easily and stays in position better than ordinary mortars.
A steel float is used to spread and finish the mortar and a very smooth
finish can be achieved. Since cement hardens by chemically reacting
with water there is no point in delaying the filling of the pool and
this can be done about 48 hours after rendering. It is not essential
to apply paints to Fibromix mortars, but, if this is not done, then,
before fish can be put into the pool, the lime released from the cement
must be removed. The easiest way to do this is to change the water after
about 28 days, the longer it is left the better. It is, of course, essential
to check the pH of the water before any fish are introduced. Pool paints
can of course be applied to a Fibromix render following the paint manufacturer's
instructions.
Fibromix, as the Complete Pool Shell
Pools are always best constructed below ground, so that the pressure
from surrounding ground and the water resist each other. Fibromix mortars
can be used to produce the complete pool shell using excavation as the
mould. The material is built up by in layers directly onto the excavation.
For structural stability and to hold the material sides need to slope.
The exact angle will depend on the material surrounding the excavation.
Strong ground conditions can provide a surface which is strong enough
to be both to be both structurally sound and to hold the render as it
is applied even on steeply inclined surfaces. An initial thin wet coat
of Fibromix can be used to help stabilise the ground before the application
of the shell. As the shell will be relatively thin it must be formed
into a curved shape to provide strength and an inverted dome is the
preferred shape.
Construction of Side Walls.
Where vertical sides are required then strong side walls are essential
to prevent the ground collapsing into the pool. Concrete blocks provide
the ideal material for sidewalls. Bricks can be used but require far
more care in selection. The load on the walls is mainly a bending, one
and avoiding long straight walls will increase the strength.
A round pool is ideal but concrete blocks, because of their size, are
difficult to lay on curves, a pool with faceted sides overcome this
problem, as shown. Where long straight sides are inevitable increasing
the wall thickness is desirable, doubling the thickness will give a
400% increase in resistance to flexural loads.
The Pool Base.
Where sidewalls are used, a concrete slab is generally used for the
base, unfortunately, frequently placed on compacted hard-core. This
is a mistake in a pool as subsequent consolidation of the hard-core
can result in support for the pool base, (slab, walls & water),
being lost and lead to structural failure of the pool. Sometimes steel
fabric is placed in the slab, the amount of steel and it’s placing
provide no useful reinforcement, it creates potential problems from
steel corrosion and is unnecessary.
The base of a pool is not normally subject to bending stresses. The
weight of the water is perfectly uniformly distributed and the ground
should uniformly resist this. The pool should be completed as soon as
possible after the excavation to avoid the base swelling and becoming
unconsolidated. If excavations are undertaken below the pool base, e
g. for drainage, these should preferably, be made level with weak concrete.
If a concrete base is used it will have to be rendered with Fibromix
to prevent leakage and this render overlapped up the rendered walls.
A single 5mm coating is sufficient. In good ground conditions a thick
concrete slab can, in fact, be eliminated entirely and a number of coats
of Fibromix render can be used as the complete base, as described earlier,
for the complete shell.
Emptying a pool when the water level in the surrounding ground is higher
than the base can prove disastrous, as the pool can then tend to float
on the ground water. Although a thick concrete slab might well resist
such pressure better than a thinner Fibromix shell this can make such
a problem worse as it can then lead to lifting of the whole hole pool
and fracture both of the walls and base. It is in fact far better, if
such a situation accidentally arises, for the base to fail and allow
the water to enter.
General Limitations.
The foregoing notes are intended to assist pool builders and it is hoped
they will help avoid unnecessary problems, work, and expense. The suggestions
are given in good faith but they cannot be expected to guarantee success
in all situations and varying strata conditions must be allowed for.
We cannot accept responsibility for the use of our materials which are
outside our full control or for the quality of the other materials used.
REIN fibres themselves are produced to ISO 9001, BS5750. Other inferior
fibres are not an alternative to REIN. Pools should only be built on
solid consolidated ground and in accordance with good building practice.
The tremendous advantages of REIN fibres have been demonstrated in the
construction of thousands of ponds since their introduction in 1983.
ADVANTAGES
• No restriction on sites.
• No unsightly creases
• Infinite choice of designs
• No limitation on depth
• Tough, long lasting material.
Ponds can easily be constructed to any design.
When completed a good couple of coats of G4 sealant
should be applied
(the above notes on construction are lifted from
a manual supplied by Reinforcement Systems of West Yorkshire. Tel 01924
882432, Fax 01924 291008)
We at All Gardens Great and Small have been using
successfully Rein Fibre for many years!
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