Leaking Swimming Pools
- For all pools repairs.
CLICK HERE for details.
Normal Usage - This includes backwashing, splashing out and evaporation.
Shell Porosity - when the waterproof membrane allows water to pass.
Plumbing Leaks - from the pipes or purification plant.
Leaks from around Perforations in the Shell
- Cement will not stick to plastic and there are various tubes and
fittings which perforate the shell i.e. the return jets, skimmer housing,
vacuum point, underwater lights and bottom drain.
Waterproofing these areas is only accomplished by careful trowel work by
the builder to ensure a "pressure-fit" between the cement and the plastic.
Unfortunately these plastic items are inclined to distort their shape
after a number of years and, generally, the larger the item the more
movement occurs. Therefore the worst culprits are the lights and the
skimmer box.
Sometimes leaks of this nature occur with newly built pools and they are
generally caused by lack of care on the part of the builder.
Cracks in the Shell - These can occur for a different reasons and normally cause a sudden water loss. These are probably the most expensive to repair.
Detecting and Repairing leaks -
As far as Normal Usage is concerned there is
little that can be done or needs to be done as long as water consumption is
not excessive. Most Chlorine products contain the retardant agent
Cyamuric Acid.
This is included in the product to ensure that the Chlorine is not
"gassed-off" too quickly by the sunlight but it never becomes consumed and
the level gradually builds up.
Sometimes it can reach such a high level that
the chlorine becomes totally locked up. Therefore a certain amount of water
changeover is necessary as the fresh water dilutes the Cyamuric acid and
keeps the level low.
Shell Porosity can be a problem, especially with older pools. The problem can be partly resolved by re-grouting the tiles but this is not a permanent solution. If the water loss is excessive, the only real solution is replace the waterproof membrane - and this means retiling the pool.
Plumbing Leaks are usually the easiest to
detect and repair.
With the water still in the pool and allowing the water
to drop (1st with the filter running and then with it off), by a process of
elimination and careful measurement, it is usually possible to determine
exactly where the leak is.
However, as most plumbing leaks require the water to be emptied anyway in
order to carry out the repairs, it is usually easiest to do a "dry test".
Each section of hidden pipe in turn is plugged at both visible ends and
water under pressure is introduced. The water pressure is read with a gauge
and, if this drops, then the pipe is leaking - as simple as that!
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A cracked shell is usually caused by subsidence of the
base.
It is assumed that the reader understands the basics of reinforced concrete
swimming pool construction.
For further information
about swimming pool construction please click here.
Generally everything depends on how severe the subsidence is -
Concrete Pillars Below the Base:-
This
remedy entails first breaking the concrete to expose the steel beams.
Then drilling down through the base with a jack-hammer to firm compacted soil (or better rock) at various points.
Then a series of reinforced concrete pillars are are
poured and incorporated with the original steel rods of the base.
The diagrams show typical pillars and their placement.
Sometimes this remedy is incorporated with a new "Gunite" shell inside the
old pool.
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Concrete Pillars within the Wall:-
This
remedy is impossible with a "Gunite" pool as there is no inner wall.
The inner blocks are removed around the the crack and a pillar formed, with steel rods inserted into the existing concrete, in order to hold the crack together.
After the pillar has been formed a GRP patch is required, either side, to take up any settlement.
GRP (Glass Reinforced Plastic) Patches:
GRP
is a very versatile material with a variety of applications - speedboat
hulls, car bodies & bumpers, water tanks, swimming pools etc.
GRP, pound for
pound, is stronger than steel and more flexible.
Click here for an Actual Case Study.
The patch is applied over the crack and bonded to the waterproof membrane after the crack has been cut out and filled.
The
main advantage is that the GRP is flexible enough to stretch over the crack
when the water load goes back in again.
Nevertheless, it should be understood that GRP is not a "miracle" product. If the subsidence is so severe that the pool is virtually "falling apart" then only structural remedies will have any chance of success.
The GRP system is so much cheaper than the structural remedies that it is normally worthwhile trying it first. Click here for an Actual Case Study of a GRP Pool Repair with Photos.
Concrete Swimming Pool Construction
It is assumed that the reader understands the basics of reinforced concrete, otherwise this is fully explained here.
The
structure of a reinforced concrete is simply a vessel to contain the water.The water is contained by the walls which, in the case of an in-ground pool, also retain the surrounding soil.
In the case of a traditionally built pool the outer wall is built first, the reinforced concrete base is then poured and finally the inner wall is built.
With a "Gunite" pool there is no inner wall and the base and wall are sprayed on during the same operation.
These block walls have no structural value and are considered to be "lost shuttering" as their only purpose is to contain or hold the concrete until it has set.
Apart from the inner wall the construction is exactly the same with both traditionally-built and "Guinite" Pools.
The
diagram on the left show a traditionally built pool with the concrete
contained between two blocks.
After the structure has been completed the walls and
floor are rendered with cement mortar, first with a weak mix coat (to level
out any imperfections, then with a stronger coat and finally painted with 3
or 4 coats of neat liquid cement (the waterproof membrane).
After this the tiles are placed in special waterproof adhesive and grouted.
Finally the border, or coronation, is placed.
Important to remember -
a. The walls have little relative strength beyond that which is required to contain the water and the surrounding soil.
b. The base is designed to carry the walls and the water over a firm sub-base.
c. The waterproof membrane is as fragile as glass.
Problems with Subsidence - There are about 50,000 litres of water in an 8'00 x
4'00 pool and this weighs 50 tonnes. The structure (walls and Floor slab)
weigh around another 30 tonnes. 80 tonnes over 40 M2 is quite a significant
loading and, unless care is taken to ensure a good sub-base, subsidence can occur.
Sometimes, no matter how much care there is, other factors can cause
subsidence (such as underground water eroding the support below the base.
Unfortunately subsidence never regularly occurs over the whole base slab and
twisting and/or bending may occur in the base slab. If this distortion is
minor it is unlikely to cause a leak in the base itself but the problem is
that, even minor distortion, is transmitted to the walls and results in a
crack that most certainly causes a leak.
One might think that, once the pool slab has moved it may settle there and not move again and then it is just a case of filling the crack(s) in the walls but this seldom works.
The reason is that, due to the twisting, the concrete fabric
of the walls has been pulled
apart but is still held together by the steel which has stretched (as it was
never designed to do any more than hold the water back).
The steel, of course, is slightly flexible and, when the 50 tonnes of water
has been removed, it tends to close the crack a little. Then, once the
crack has been repaired and the 50 tonnes of water has been put back, the
steel stretches again - and the crack opens!
<< Back to Repairing Cracks >>
Reinforced Concrete - the Basic Principles
Concrete, by nature, has great resistance to crushing. However, as it is composed of non-integrated elements, it is relatively easily pulled apart.
Steel also has great resistance to crushing and is almost impossible to pull apart as it would simply just elongate. Steel reinforcing rods are placed in concrete to overcome its weakness to being broken by pulling apart.
The
diagram on the left shows a simple reinforced concrete beam, spanning two
supports with a heavy load in the centre.The
load would tend to cause the beam to bend and break in the middle.
What is happening is that, due to this bending, the fibres of the concrete
are being crushed at the top of the beam and stretched at the bottom.
The concrete is easily able to resist the crushing and, because there is a
steel reinforcing rod at the bottom (to take the strain of the stretching)
the beam does not break.
It is not quite as simple as this as the beam has to resist other mechanical forces, such as twisting, lateral splitting etc. and the steel system has to be more complex than a simple beam at the bottom but this should explain the basic theory.
Now
when it comes to using reinforced concrete to construct a swimming there are
3 factors to be considered -
1. The walls are designed to contain the weight of the water without bulging outwards and, in the case of an in-ground pool, the weight of the surrounding soil without bulging inwards.
2. The floor to carry the weight of everything (water, walls and itself) without cracking or twisting.
3. The ground below the base has to be sufficiently stable (i.e. compacted soil or rock) or made stable with hard fill - in order that there is no chance of subsidence which could cause distortion of the base and prejudice the whole structure.
There are about 50,000 litres of water in an 8'00 x
4'00 pool and this weighs 50 tonnes. The structure (walls and Floor slab)
weigh around another 30 tonnes. Therefore we have a combined weight of 80
tonnes over an area of 40 M2 (2,000 Kgs. per M2).
A pool is quite different from another type of structure (such as a house)
as the smallest amount of subsidence can cause a "hair-crack" which would
make the pool leak.
<< Back to Swimming Pool Construction >>