bluepools

Winter pool construction

Hi again

We are still building the large pool near Montflanquin in Lot-et-Garonne - pronounced "Monflankey" in French - we have just started on the paving flags. The weather should be warm enough to screed the pool and install the liner in early April. The experts among you will know that it is very risky to install the screed and liner in low temperatures and so we just build the pool structures through the winter and then have a mad rush in April and May to get the pools finished for the coming swimming season. We will have built another 8 pools since those described in my last post. These will all have to be finished this spring and so we will soon be very busy!  We will post some pictures of them when they are fully operational so that you can see what we have been doing for the last very wet and cold 4 months.

I know that you are all interested in the problems that we come across and how we get over them. We have just had a tricky problem with a pool that we are building near Montendre - just to the south of our base here in Jonzac.

The sight is sloping and when Luke priced the project in the autumn the site was very dry and it looked like a very straightforward job as we knew that the subsoil was impermeable clay and so ground water should not be a problem.

We were correct in that ground water was not a problem but the topsoil and the thin sand layer beneath it was totally saturated from all the recent rain. Being on a hillside the pool excavation just filled up with water as  it was being dug and all the sand and topsoil was washed into the hole - the construction conditions were just impossible.

So how did we get over this?

We excavated a trench on the two uphill sides where the water was coming from, installed black depannage land drain pipes laid in a 40mm silica gravel bed that was wrapped in a geotextile membrane. This land drain was connected by UPVC plastic pipe that discharged into a disused well. This worked perfectly and enabled us to build the pool in relatively dry conditions. The project was delayed by about 4 days, the cost to the client was less than 2000 euros and he now has a land drain that will keep the pool fully protected from excessive water pressure in wet winter periods.

Because of our engineering background  we always overcome such problems at minimum inconvenience and cost to the client - many of the "amateur" builders that install the kits would have thrown up their hands in disgust and walked away from this project.

I attach a sketch of the drain and some pictures below.

The middle picture shows the UPVC pipe taking the water away to the old well.

On the other picture the red sprayed line is where the pool walls will be located - the site is now dry and suitable for pool installation. The white material is calcaire laid over the land drain to provide a working surface.

Regards

Will Witt

25th March 2007

Why pool projects can go so badly wrong

Will Witt 19th July 2006

I was a bit shocked at the weekend when I realised how long it has been since we added any posts to this blog and so I will be making a special effort to keep it more up to date. As promised I will bring you up to date with the pools that we have built recently at the weekend.

During a long drive back to the office from the site of a pool that we are building near Mirande in Department 65 I was reflecting on the lessons that we have learnt from recent projects and thought it might be useful to share these.

Water, water everywhere!

The most striking issue is that of the last 6 pools that we have built - we have found large volumes of water during the excavation for 3 of the pools. This always causes a major problem because:

• The water makes the ground supporting the pool unstable
• It is impossible to complete the pool unless the water level can be reduced
• The likelihood of catastrophic failure if the pool ever needs to be emptied

Why is the water there? - it may be leaking drains or the effluent from a sewage filter bed fed by the fosse septique or water from the roof drainage. These are all easy to deal with because the flow can be diverted or blocked off. But what if the water is there because of a high ground water table. There may be millions of gallons in the hill above your property that makes it impossible to drain your pool excavation.

In all the three pools mentioned above the water was caused by a high ground water table. This highlights why a site investigation is so necessary - but even a site investigation may not discover that there is water problem because the ground water table level will vary from summer to winter and can even rise half a metre after an intense summer storm.

How do we get over this problem?

The solution always depends on the sub-soil conditions at the site.

If the sub-soil is gravel it may be impossible to build the pool below the ground water level - particularly in late winter or early spring when ground water levels are at their highest. The only solution is to lift the pool level and provided it with decking and-or landscaping to integrate the pool into its surroundings.

If the subsoil is solid clay it is unlikely  that ground water is feeding into the pool excavation and so  a drain needs to be installed beneath the pools lowest level and the water pumped out.

In really difficult circumstances (this applied to all of the 3 pools mentioned above) - the ground may be a mixture of clay, gravel and or rock with seepage occuring at various levels. In these circumstance each pool needs a bespoke solution that may involve numerous wells with pumps and large volumes of reinforced concrete to stabilise the foundations of the swimming pool - this is what we did in each case.

What are the implications for pool purchasers?

The most obvious implication is that it is very difficult to install a kit pool in these circumstances - if you have bought a kit and hit water during installation fill the hole up to about half a metre above water level with concrete and build the kit pool walls up from that level.

What do you do if you think you have water logged ground in your garden

You could consult an expert but because there is a bewildering variety of kits for both above ground and inground pool installations on the pool installation market as well as the traditional installers that build reinforced concrete filled concrete block and rendered pools with liners, reinforced concrete filled polystyrene block pools with liners (As we install) and tiled reinforced concrete pools it will be difficult to get objective advice. I recommend that:

1. If economy is your main consideration - buy and install an above ground kit pool
2. If you must have an inground pool get a traditional installer to provide a liner pool because below ground pool  kits are not suitable for waterlogged ground - and tiled pools leak! - see elsewhere in this blog.

What other problems have we come across recently?

We keep meeting clients (or are told about friends of clients) who have had problems because their pool installer has run into financial difficulty.

The reason for this happening is that pool installation is a very competitive and risky business and this results in numerous bankrupties of quite large French companies.  There are many  installers that cut their margins to get work and this results in the following:

• Poor or non-existant after sales service
• Non-completion of pools after the builder has received most of the money
• Failure to replace faulty parts

What can you do about it?

What you cannot do is to refuse to pay the pool builder any money until he has finished the pool. None of us could operate on that basis because the cost of the materials and labour involved is so high that we would effectively be operating as bankers as well as pool builders

What you can do is

Ask your pool builder for:

• References from 3 recent clients of the pool installer - pick one and telephone him
• A balance sheet from the previous years trading
• A sight of the company bank statement that is less than 3 months old

These three simple checks may reveal issues that you are not comfortable with - if your pool installer cannot provide a satisfactory explanation then go elsewhere!

What else have we discovered recently?

We install the best quality pump and filtration equipment (manufactured by Hayward) that is designed to provide a complete pool water change in 6 to 8 hours. Even with this equipment we still find that pool water quality can sometimes be a problem. We can only imagine what the water quality is like in pools that only provide a water change every 20 hours or so.  We have also found that many other manufacturers pumps fail quite quickly and that their fiberglass filters can split and leak.

Pool Alarms

We are all waiting to see if the law is going to change so that pool alarms are outlawed. We find it quite odd that many people install an alarm at an unoccupied property and assume that they are complying with the law. The alarm is only lawful if there is someone within earshot of the pool that can respond to the siren.

In our experience pool alarms are very unreliable - but the makers require the alarm to be returned to them if faults arise - but how can you be complying with the law if the alarm is being repaired elsewhere.

Pool safety fences mat not be attractive - but they do work and with a bit of careful design they can be largely hidden behind shrubs etc.

Regards

Will Witt
Bluepools SARL

Why rectangular pools cost more

Introduction

This week I am tackling another very topical and also technical issue. My objective is to help the pool buyer to make a choice between a rectangular pool built using traditional technology or a circular pool or pair of linked circles that rely on tension in the pool walls.

Bluepools installs the rectangular type of pool in reinforced concrete.

The Double Bubble pool manufactured by Christal Pools and sold under licence in France by Piscine Plus is probably the biggest selling product of the circular / kidney shaped type and is made from galvanised steel.

There are also rectangular pool kits available on the market and so I have also considered these as well.

All these pools rely on PVC liners - we dealt with pools that incorporate ceramic tiled finishes in the post dated 7th January. Ceramic tiled pools that are built properly are 2 or 3 times as costly as the pools that we are dealing with here.

How the different types work

The Bluepools approach

The pools that Bluepools constructs are based on walls that are supported by a foundation beam around the outside of the pool as shown in the following sketch. The concrete wall is reinforced with 8mm high tensile bars that also connect the wall to the foundation.

When the pool is empty (sketch on the right) the earth pressure behind the wall is resisted by the pink pressure underneath the wall foundation.

When the pool is full the pink pressure changes shape as shown. The wall is stable under all types of ground loading provided that the wall is founded on good ground.

One of the main advantages of this type of pool is that the earth pressure loadings on the wall can vary from zero (ie no soil against the wall) to very high (water-logged running sand) and the walls will still be stable - provided that the foundation below the wall is good. Poor foundation conditions below the walls may require deeper excavation down to good ground and backfilling with concrete.

Roman ends and steps of all shapes and size can be freely installed in pools of this type.

Many French artisans also build pools in a similar way but they often replace the wall foundation with a reinforced concrete slab that covers the whole pool floor. This is not really necessary when the ground conditions are good.

The heavier nature of the construction of reinforced concrete rectangular pools (and the higher capacity filtration equipment required- see below) results in a cost penalty of about 200 euros per square metre of pool area.

The kidney shaped pool approach

The kidney shape approach is illustrated on the following sketches.

When the pool is empty the ground pressures are resisted by compression in the galvanised sheet pool walls and when the pool is full of water the compression changes to tension.

It is very important that the backfill around the kidney shaped pool is a consistent sand that is uniformly compacted. The tension / compression in the pool walls is taken to a heavy beam that spans across underneath the pool at the point where the two circles meet - as shown in the following sketch. The walls are stablised by concrete that is cast between the sheet steel walls and the side of the excavation. The kit relies entirely on the galvanising to stop corrosion.

The heavy main beam must be supported by good ground and it is very important that the sand backfill around the walls is uniformly compacted to ensure that wall loading is even. This means that the backfilling must exist right around the perimeter of a kidney shaped pool.

Small sets of steps can be installed in circular pool wall but they are a  complicating factor in a structural type that relies on hoop tension in the walls of a pool.

The Christal Pools design is protected by patent and hundreds have been successfully installed and used in France for over 10 years.

Rectangular pool kits

There are many different types of rectangular pools that can be purchased in a kit format. There are many different structural systems available. Some rely on a prop from the bottom of the pool excavation, some rely on anchors in the soil surrounding the pool and some seem to rely on blind faith!!!

Some are very cheap and some are very expensive.

Many originate from overseas where consistent dry ground conditions - such as in various areas of the US - allow the use of very light systems.

The universal truth that applies to all of them is that they rely on the ground for support but are never bespoke designed for the installation site. Ground conditions and environmental loading on pool walls in SW France are highly variable and anyone that purchases a rectangular pool kit is taking quite a risk.

Water treatment and filtration

The main wall of kidney shaped pools is a thin galvanised sheet that is not wide enough or strong enough to support conventional skimmers, inlets and vaccuum points through the walls of the pool.

As a result all the pool "through the wall" fittings are incorporated in the ladder and this restricts the rate at which the pool water that can be filtered and chlorinated. This results in a reduced capacity in terms of the time it takes for the pool water to be changed. The pumps and filters are sized to suit and it is very difficult to get the 6 to 8 hours water change period in larger pools (As  recommended for private pools for family use). Skimmers also take off the surface water where any harmful pollutants or viruses are concentrated. The intakes through the pool ladder do not do this as efficiently.

It is also true that the circular shape of a kidney shaped pool promotes better mixing of the water than in a rectangular pool with its corners. Most circular type pools are also built without a hopper (deep end) and this also increases the water circulation efficiency.

As a result the water circulation and filtration system in a kidney shaped pool can be installed  at a cost  that is a good bit less than the equivalent cost for a rectangular pool. However on the other hand it is very difficult - if not impossible - to meet DDAS standards for community pools for instance. (We are preparing a future post to deal with DDAS standards for gite complex pools)

Property Valuation

The shape of a kidney pool makes it impossible to integrate the coping stones and the surrounding paving. At many installations the paving runs under the coping stones - this is both unsightly and a trip hazard.

Many people prefer the classic lines of a rectangular pool with a Roman End and surrounding paving where the joints in the coping stones (margelles)  are continued through the paving slabs (dalles). This has the affect of increasing the value of a property where a rectangular pool has been installed.

Conversely many people do not like circular type pools and so the value of the property may even be decreased if people take the removal of an existing pool and replacement by a rectangular pool into account.

Summary

In summary - rectangular pools are a very different product from a circular pool and will normally be about 10,000 euros more for a pool of about 50 square metres in area.

Rectangular pools in reinforced concrete can be adapted to suit any ground conditions.

A kit pool of any type is not suitable for highly variable or poor ground conditions.

Kidney shaped pools are an excellent product when used as a leisure facility for a single family.

If a pool is required for a gite complex rectangular pools are necessary to meet DDAS requirements

Rectangular pools that are carefully designed and built increase the value of a property -  circular or kidney shaped pools may detract from the property value.

I hope this helps in your choice of pool - it may be be a difficult decision but the two options are really quite stark:

• If you want to enhance the long term value of your property buy a rectangular pool with a structure built from reinforced concrete
• If you just want a pool for the family to swim in and enjoy then buy a Christal Pool

I know the people at Christal Pools and I think that they have an excellent product - however the pools that we build are aimed at a different market - I hope this short analysis helps you make a choice on a more informed basis.

Regards

Will Witt

 

Why has the paving around my pool settled and cracked?

Introduction

Last week we looked at the highly technical issue of why tiled pools leak.

This week I want to look at a slightly less technical  issue but one that is of fundamental importance to pool buyers - the failure of pool paving. It is interesting that the answer to the question posed in the title above is exactly the same as the answer to "why do tiled pools leak" ie  "Most paving cracks and settles because of faulty design and installation procedures"

It is worth remembering that a pool is a hole in the ground, filled with water and surrounded by paving. So the paving will always make or break the appearance of a pool.

First of all what do we mean when we say paving?  It is an engineering term that refers to a hard surfacing laid on the ground for use by pedestrian or wheeled traffic.

In the context of pools the hard surfacing is the area around the pool that is needed to:

• Drain rain water away from the pool so that dirty water, sand and earth does not drop into it
• Allow use of the pool in wet weather so that bathers do not carry mud and dirt into the pool
• Allow access to the pool throughout the year for maintenance
• Discourage frogs and other amphibians from using the pool

- and last but not least for sunbathing and entertaining!

We will examine how pool paving is normally built below.

The background

Lets look at what happens when a pool is installed. First of all a hole is dug in the ground. This hole has to be bigger than the pool area to allow space for wall erection and the pool pipework. This  is known as the pool "overdig". Many of the kit pool manufacturers boast about how small the overdig requirement is for their particular pool design. This is misleading because the main benefit that accrues from a small over dig is a small saving in excavation and backfilling costs. Most kit pools also require the top of the pool wall to be stabilised by a concrete "ring beam" that runs right around the perimeter of the pool and so a narrow overdig also reduces the volume of concrete required.

You are probably wondering what all this has to do with the paving, but if the soil is poor - and it nearly always is in the top metre of ground in SW France - the excavation weakens the surrounding ground as shown in the sketch below - and it is this soil that supports the paving.

The excavation will always weaken the volume of soil shown in the sketch unless the ground is solid rock. If the soil is clay or sandy clay the horizontal restraint from the soil that has been excavated is removed and the wedge of soil tends to stretch horizontally and  the vertical face of the excavation moves towards the pool.  In fact in our experience quite large elements of soil often do fall into the excavation thus considerably widening the "overdig". There are other consequences from this method of construction:

• The gravel fill that is supposed to reduce the soil loading on the kit pool wall absorbs water (it is a hole in the ground) that overloads the pool wall and keeps on softening the already weakened soil
• The concrete anchor beam on which the kit pool relies for stability is supported by weak soil that has been badly disturbed at the ground surface by pool construction operations
• The kit pool designs never take the loading from the weakened soil into account - this is always written out in the fine print of the contract
• The paving settles and cracks

I have concentrated on kit pools because they suffer from a major disadvantage when considering how the pool paving can be installed in such a way that it does not settle and crack. This disadvantage is that the pool walls are so light that they cannot be used to support the weight of the pool paving.

The pool paving specification

There are 3 basic options:

1. Paving slabs - 15 to 35 mm thick - laid on a thick sand bed
2. Ditto laid on a sand bed on a consolidated stone base 150 to 200 mm thick
3. Ditto laid on mortar on a 150 mm thick reinforced concrete slab

Type 1 should never be used - the slabs will always need constant lifting and relaying.

Type 2 can be used when the ground is good - see below.

The only form of construction that can be guaranteed to work in most of the weak surface soils of SW France is Type 3 as shown in the following sketch.

Note how the large diameter 16 mm high tensile steel dowel bars transfer the weight of the reinforced concrete slab onto the top of the pool wall. 

The sketch also shows how the paving is supported by the reinforced concrete slab that in turn is supported by the pool wall on one side and by undisturbed ground on the other side. Reinforced concrete is the only type of pool structure that is capable of providing this type of support to the pool paving - so if a kit pool is installed - the paving is likely to settle  and crack unless the pool is built in very good ground such as rock or dense gravel (in these circumstances the paving can be supported as described in 2. above). As noted in previous posts on this blog most pools in SW France are built in poor ground and so the likelihood of having a problem with paving built around a kit pool is quite high.

Paving slabs

There are a few other issues regarding the paving that are worth noting.

Frost

Overnight temperatures as low as -10 degrees Celcius are quite common in SW France. Frosts as hard as this will break up all thin medium to low density paving slabs. High density slabs 35 mm thick are recommended - and even some of these may fail from time to time.

Grout

Paving durability and appearance depends on the grout - and the proprietary grouts that are needed are quite expensive - make sure that any paving is laid with grout that comes in a bag that shows that it is intended for use outside with heavy duty slabs. Use of anything else is a false economy as the grout may need to be relaid after the first winter.

Falls

Both the reinforced concrete support slab and the paving needs to be laid at a minimum gradient of 1 in 60 falling away from the pool. If  the paving boundary is formed by the wall of a building you must install a drain or the wall will get very damp and water may even enter the building when the floor level is lower than the pool paving outside.

Joints

To obtain a stunning appearance the margelles (coping stones in English) and the dalles (paving stones in English) must be manufactured by the same maker so that the joints can be lined up. With care - and if the pool is built to the right size - the dalle and margelle joints can be made to line up  both across and along the length of the pool.

Laying Margelles

The top of the pool wall must be absolutely flat and level or the margelles will look dreadful - this can be very difficult to achieve with some kit pools where manufacturing tolerances are too large.

Type

Bluepools offers 35 mm thick Sahara or Ardoise paving by Carra Terra as a standard on all its pools. These are supported in all instances by a reinforced concrete slab spanning on to the pool wall as described above.

Cost

High quality paving including the reinforced concrete slab and the paving slabs will cost of the order of 100 euros per square metre. The margelles will cost between 300 and 800 euros depending on the pool size and the Roman End / steps configuration.

Remember the pool paving will make or mar your expensive pool - do not economise on it.

I will be writing a post on choosing between paving and decking in the next few weeks - so please look out for that if you are in the process of planning a pool.

Regards

Will Witt

 

Why do most tiled pools leak?

Introduction

I have written this short paper because many people ask us if we can build a tiled pool in our operational area in SW France and our answer is always "Yes - but it would be very costly and we do not build them"

The provocative question posed in the title of this weblog can be answered with the simple statement  "Most tiled pools leak because of faulty design and installation procedures"

Let's take look at what is required in ensuring that a tiled pool does not leak and then compare the technology with PVC liner pool technology.

The design and construction of tiled pools

Tiles can only be placed on walls and floors that are structurally rigid and that do not flex under water pressure, ground pressure or temperature change. If flexing occurs the tiles will come off. The tiles themselves are not water-proof and so the structure itself has to provide the water-proofing.

Across the globe such structures are often formed with Gunite that involves projecting concrete pneumatically at high speed onto a natural ground surface or onto a formed surface using shuttering. Reinforcement consisting of steel wires or rods is put in place before so that the gunite surrounds them and becomes "reinforced concrete". The method of construction allows both curved and flat shapes to be formed and is in common usage in Australia and the US. It does require good ground conditions because it is impractical to build thick sections using this technology.

In SW France the ground conditions are often poor at pool sites and so conventional reinforced concrete construction would be required. This involves the construction of a heavily reinforced  slab base (250 to 300 mm thick) and walls (180 to 200 mm thick).

In either case the structure must be designed by an experienced fully qualified civil / structural engineer who will take all the ground conditions, pool size, pool depth etc into account.

The most important construction issue relates to the joint between the heavy ground slab and the walls. The slab obviously has to be cast first. The shutters for the walls are then erected and the walls concrete poured a day or so later. This results in a joint that is virtually impossible to water-proof in a 200 mm thick wall.

Hence the water-proofing is provided by a water-proof membrane that is applied to the surface of the very expensive pool structure. The quality of the membrane and the leakiness of the pool relies entirely on the materials used, the mix proportions, the mixing and the skill and integrity of the plasterer.

Other pool construction issues

There are various other construction  issues that need to be taken into account in the design and installation of a ceramic tiled pool and these include:

1. The concrete base slab and the walls will need to be cleaned by water blasting, shot blasting, grit blasting etc to ensure that the render / screed sticks on - these are all very dirty processes that take a lot of time to undertake
2. The concrete base slab and the walls will need to be levelled with render / screed  to get the necessary flatness for tile installation (< 3mm in 3m) - this may also need cleaning before the membrane is applied
3. After levelling the waterproof membrane will need to be applied - this will be a proprietary latex based product mixed with Portland cement that will stop moisture penetration, moisture expansion, chemical attack by chlorides and efflorescence. The membrane will need to cure for 7 days at 20 + degrees C.
4. After curing the pool will need to be flood tested for leaks - this will involve filling at a slow rate of 600 mm in 24 hours. Fugitive dyes and a scuba diver will be required to locate any leaks
5. Mosaic tiles will need to be paper faced ceramics as back mounted mosaics can come off the wall following saturation and pool water chemical attack
6. Tiles must be impervious or vitreous to reduce the effects of moisture expansion and to eliminate freeze / thaw problems
7. The tile mortar bed must be latex based to reduce chemical attack and improve flexibility to withstand moisture expansion and shrinkage or epoxy based (expensive and can be difficult to use)
8. The grout can be latex based or epoxy based - epoxies can discolour under sunlight.
9. Movement joints must be provided in the tiling in strict accordance with the grout manufacturer's installation instructions
10. The latex based beds and grouts will need to cure for 14 days at 20 degees C (10 days for epoxies)
11. Pool to be filled at 600 mm per 24 hours to prevent excessive water pressure, thermal and moisture differentials. Filling should not proceed in direct hot sunlight or with very cold water

It is no wonder that these sorts of pools take so long to build and are so susceptible to leakage.

Pool Operational Issues

The control of pool water chemistry is very important in ceramic tiled pools:

1. Chlorine uses and depletes calcium and so calcium balance is essential to prevent deterioration of cement based grouts and mortars
2. If the pH is too high mineral deposits will form on the tiles and grout - they can form under the surface of the ceramic tiles causing the surface to come off the tiles
3. If the pH is too low acidic etching of the grouts and mortars can occur
4. If the calcium hardness is too low the pool water will etch calcium from the grout and if it is too high calcium deposits can form on any of the pool surfaces
5. At normal pH values iron and copper metals will come out of solution and can then be deposited as stain on tiles, grout and pool fittings

Another common problem is that the skimmers become loose in the concrete wall in which they are built. This results in leakage that can only be cured with putty that is unsightly and likely to be picked out by small fingers!

PVC liner pool technology

When everything is taken into consideration it is difficult to understand why anyone would want to take the risk of building a ceramic tiled pool - that is why we do not build them!

PVC liner pools:

• Will not leak even under quite large structural movements in the pool walls and floor
• Can be renewed comparatively cheaply (800 to 1000 euros) and easily on a DIY basis
• Allow leaks to be easily located and repaired (this will be the subject of a future weblog)
• Are virtually impervious to chemical attack (calcium deposition can occur but PVC is much easier to clean than tiling and grout)

And last but not least they look terrific!

In summary PVC liner pools cost half of what ceramic tiled pools cost and are superior in just about every way. They are based on the latest material technology and are environmentally friendly because of the reduced requirement for energy intensive cement and steel products. Ceramic tiled pools are based on 40 year old technology that relies on modern chemical additives to work!

Will Witt

 

Pool near Cognac

Last week I promised that I would keep you updated on the pool that we are installing near Cognac in very difficult ground conditions. The first picture shows what happened when we started to excavate for the main drain under the hopper that we installed last week. The water eventually rose to the top of the trench - see the fourth picture.

The second picture shows the drain excavated down to 500 mm below the bottom of the hopper. The geotextile that will stop any fine material from clogging the drain and the 300 mm pipe that will act as the pumping chamber have been installed.

The third picture shows the drain filled with stone.

The fourth shows the foundation to the walls of the pool ready for concrete - we managed to pour the entire wall foundation on Friday despite a day of rain. It also shows that the groundwater table is at about the top of the hopper.

To build the hopper we will need to run a submersible pump at the bottom of the concrete pipe pumping chamber continuously until the liner is installed and the hopper is full of water.

The moral is - if you live in a valley - especially near a river or stream - you need professionals to build your pool.

Until next week.

Will Witt

Bad ground conditions

We have just started a new installation in the Cognac area. The land is quite low lying and beside a stream - so we anticipated that it might be quite problematic.

And it is!

The top metre is filled ground, underlain by very soft clay with running water at the bottom of the fill. We are contracted to install a 1 metre deep hopper.

We have already decided that the pool floor will need to be in reinforced concrete, and we are now working out how to build it underwater!.

Joking aside we will install an underpool drain with a submersible pump to allow us to dewater the excavation and this will be left in place for the client to dewater the surrounding strata whenever he needs to empty the pool.

This is just another saga in a long list of installations where a kit type pool would either be impossible to install - or would fail during the first time that it is emptied.

We will let you know how we get on with this project next week.

Bluepools wall construction system

All of our pools are constructed from 250mm wide polystyrence blocks which are filled with reinforced concrete. In good ground conditions, the walls are erected on a heavy duty concrete strip foundation. In poor ground conditions, the walls are erected on the reinforced concrete slab that is installed to form the pool floor.

For the pool user, the major benefit of walls constructed from polystyrene blocks is that the walls are insulated and can maintain a higher water temperature without heating. If pool heating is installed, the heating costs will be reduced. It also gives the walls a soft and luxurious feel.

The wall system has the following structural advantages; it can be safely adapted for all ground conditions, it can accomodate underpool drainage where necessary, it is very quick to build, it does not involve the lengthy and highly skilled process of rendering, it is not susceptible to bad weather.