NSPI GUIDELINES FOR CONSTRUCTING GUNITED OR HAND PACKED CONCRETE DOMESTIC POOLS UNDER NORMAL SOIL CONDITIONS
(UP TO 60 M² FLOOR AREA)
(Please note: This document contains guidelines ONLY and the NSPI cannot be held responsible for any deviation from these guidelines)
Normal conditions June 2010
Loam soil or better
Bearing capacity 100 kPa (= 10 m head of water)
Turf, clay, rock, collapsible soil or high water table etc, is excluded.
Flat / level surface
Abnormal conditions
It is recommended that an engineer be consulted for any conditions other than ‘normal’. This would be for the account of the client.
Excavation
Mark out: Pool perimeter must allow for concrete/gunite and steps to be cut out of natural soil, or backfilled and compacted to 93 Mod AASHTO (SABS specifications)
Level: Should allow a 20 mm variance over total length of pool
Digging Depth to be measured from under the coping (not water level)
Excavated wall
To be perpendicular to floor (approx. 90º angle)
Excavated ring beam to be 300 mm x 300 mm
Excavated hole to be over-excavated by 150 mm to allow for concrete/gunite
Excavated floor to be compacted to 93 Mod AASTHO
Acceptable dimension variations on finished pools
2. 5% on perimeter
5% on other measurements
Steel reinforcing (see sketch on right - click to enlarge)
A single layer of reference 156 steel weld mesh, together with R8 rods at 800 mm centres, or Y10 high tensile steel bars at 1m centres. Secure with rust proof ties, e.g. galvanized binding wire.
An additional layer of 156 steel weld mesh required for corners, which must overlap by 1m on both sides (achieved by commencing/ending at the corners, but overlapping).
4 x Y10 bars in ring beam, spaced 100 mm and to be continuous.
Weir, lights, aim flows are to be placed between steel bars, which are not to be cut.
Top step to form part of the ring beams Y10 bars to extend to top step edge. Additional steps to have its own Y10 bar at edge, into the mesh.
All steel to be overlapping by a minimum of 500 mm at joints.
Alternative methods:
R8 rods only to be placed 200 mm centres throughout the pool, and tied at each intersection.
Y10 steel bars only, to be placed at 230 mm centres throughout the pool and tied at each intersection.
Approximately 3.8kg/m² steel to be used.
Concrete Pool Shell (see sketch)
General
Excavated 90° corners to be filled with concrete and then to round-off corners (for automatic cleaner, and the additional concrete strengthens pool shell)
The steel to be positioned into concrete 100 mm below surface (50 mm off the ground).
Concrete strength to be 30mpa at 28 days.
Caulk in weir, lights, aim flows well.
Do not use rebound or re-wetted/mixed concrete on ring beam.
Shell to be watered twice a day by owner for at least 4 days after concreting.
Minimum curing period 7 days, before applying interior finish or heavy compacting.
Guniting
Walls and floors to be a minimum of 125 mm thick
The mix is to be 4:1 river sand/cement by volume. Correct gauging to be achieved and mixed well.
Walls and floors to be a minimum of 125 mm thick
River sand to be coarse, sharp, double washed, clean and well graded, with maximum size not to exceed 1 mm. If any alternative sand is used then care must be taken to achieve 30 mpa.
Gunite mix to be applied at 3 bars with the nozzle between 900 mm – 1200 mm away from surface.
Hand pack
Walls and floors to be a minimum of 150 mm thick.
Use an approved Ready mix to be delivered to site on the day, and no water to be added during application process, which should be done same day.
Should Ready mix not be available, use river sand (see gunite) and crusher aggregate with a minimum of 13 mm, plus cement (4:1 mix by volume)
Lights, aim flows and weir
Where possible, lights not to be installed under a sundeck nor too deep, for easy access.
Where possible electrical conduit to be installed under surround.
Every pool is to have a suitable number of aim flows installed to ensure sufficient circulation.
Weir and aim flow to be positioned for optimum circulation. and with shortest piping to filtration.
Coping
To be laid to manufacturers specifications if available, or
To be laid onto a wet mortar mix for all types of material other than tiles.
Tile adhesive to be used for tiles. Adhesive and grout to have waterproofing qualities.
To be laid level (use water level) onto pools edge, but a tolerance of 10 –15 mm may be acceptable on bottom, but to be flush at top, depending on type of material.
Where suitable, coping may overhang mosaic tread for splash back.
When renovating, old coping and screeding to be removed completely and old concrete surface to be cleaned thoroughly. All cavities to be filled with a 3 : 1 river sand/cement mix, and bonding liquid to be applied prior to new screeding.
Waterline Tiles
Waterline tiles to be laid at waterline approximately 150 mm wide, onto a wet mortar mix.
If porous tiles are used, adhesive and grout to have waterproofing qualities.
When renovating a pool, old waterline tiles and plaster to be removed and area to be re-plastered prior to affixing the new waterline tiles.
Surround
To manufacturers specifications.
PUMP / MOTOR & FILTER
Specification relating to the size of filter necessary for various pool sizes
Diameter Weight of media
Up to 15 000 litres + 450 mm 40kg
15 000-30 000 + 500 mm 80kg
30 000-55 000 + 600 mm 120kg
55 000- 85 000 + 600 mm 160kg
85 000 litre + + 750 mm 200kg
Specification relating to the size of pump and motor used in conjunction with each filter
1-bag 0.4KW motor
2-bag 0.6KW motor
3-bag 0.75KW motor
4 & 5-bag 0.75 & 1.1KW motor
Some installations may require bigger pumps, depending on pool layout and extras e.g. solar, water feature. Suppliers/manufacturers warranty conditions are to be observed.
The above table is based on the pump being installed approximately at water level and the suction pipe not longer than 6 metres from skimmer box (weir). For any additional height, distance and/or accessories the above should be recalculated. Please refer to the pump and filter flow chart.
Install in level position and line up with each other. Preferably do not install with concrete base, but loose crusher may be used to look tidy.
Cartridge Filter (synthetic fibre)
Size and usage as per manufacturer’s specifications.
Solar heating
If possible, a separate pump/motor and suction point is recommended for
solar panels. Refer to solar panel manufacturer’s specifications of solar panels,
pump/motor and filters.
PIPING AND FITTINGS (PVC & Poly)
All piping to be class 6, and PVC piping must also carry SABS mark.
To be laid into a trench of at minimum 350 mm deep, onto suitable soil, backfill or river sand. i.e. no sharp objects.
Piping is not to be bent, e.g. correct fittings are to be used.
All connections to equipment to be joined with unions, e.g. pumps – 2 unions.
If pump is below water level, install ball valves to suction and returns.
If pump is above water level, non-return valve may be installed.
Install ball valve to all water features.
Suction line to be at minimum 50 mm PVC or poly piping, and to be continuous if poly piping is used, or as continuous as possible if PVC piping is used. But for extended distance, use 63 mm piping.
Return lines are to be at minimum 50 mm OD PVC or 40 mm ID poly pipe.
T-piece on return lines is recommended to be midway between 2 aim flows for even pressure.
Position of backwash pipe outlet to meet local authorities’ regulations. It should preferably not be longer than 3m and never run uphill. If longer, compensate with 63 mm piping.
All fittings must carry class 6 rating and PVC pipe glue class 14. Poly pipe clamp bands must be stainless steel.
Assure PVC connections to be cleaned using sandpaper or PVC pipe cleaner before being glued. Use sufficient glue on PVC/poly piping/fittings to avoid leaks, and on completion clean off excess glue for neatness.
INTERIOR FINISH
MARBLE POOL PLASTER
Onto new concrete surface
A dry mixture is available in various makes, colours and grades.
It can be stored off the ground under cover for up to 3 months.
Other marble pool plaster related products are available for various functions (refer to suppliers).
It is suitable as an interior pool plaster finish on all types of concrete surfaces, but not for use above water line.
The new concrete surface is to be straight and firm, but rough for to key, and clean and free of dirt.
1 x 40kg bag covers approximately 2m².
It is mixed on the pool floor (shallow end) to a very stiff but workable consistency (approximately 6 – 7lt clean water/bag).
Calcium may be added to the water (160g/bag) to accelerate hardening.
(Preferably do not use calcium flakes – particularly when using coloured pool plaster)
Apply in 1 day with special trowel approximately 6 mm – 7 mm thick to a smooth finish, commencing at shallow end wall, to deep end wall, deep end floor ending shallow end floor etc. No water must collect at deep end, which will prevent proper curing and cause failure.
Avoid rain, frost or strong winds while applying the marble based pool plaster and until filled with water.
Allow marble pool plaster to cure, check/repair the next morning blemishes/shrinkage cracks and commence filling water (deflected into deep end) continue to fill (owner) continuously until 5 cm below coping.
If rain is imminent or in very hot conditions, gently wet side walls hourly (by owner).
On previously marble plastered surface (renovation)
Empty pool and clean out if required.
Prepare surface, cut neatly under bottom of mosaic surround (unless mosaic tread is renewed) and totally remove previous marble pool plaster for up to 300 mm below mosaics to assure flush new plaster application adjoining mosaics.
Chip entire remaining pool surface 6 mm deep at 50 mm centres. Remove all hollow or loose marble plaster.
Thoroughly clean surface.
Mix slurry with marble plaster in a 4:1 water/flex bond solution, and apply to surface in a rough texture in order to key.
Preferably apply new marble pool plaster the next day but do not delay it longer than 5 days.
Then follow all marble pool plaster instructions as on New Concrete Surface.
FIBREGLASS LINING OF POOLS (as an interior finish)
FIBREGLASS AND POLYESTER RESIN
SCOPE
This standard specifies the requirements for the materials and construction of glass fibre reinforced polyester swimming pool linings. These are intended for the lining of both old and new concrete pools and for old marble-based plaster pool linings.
Both cosmetic lining and the resurfacing of a leaking pool (this is a pool that is generally in good condition and has only plaster cracks).
It is implicit that the fibreglass lining of pools should not be attempted by people who do not have the experience in laminating and it should thus be left to proven contractors.
TERMINOLOGY
Accelerator
This is liquid compound called cobalt and is used to reduce the gel-time and/or increase the hardening rate of resin.
Barcol hardness
This is a scale according to which the hardness of a fibre-reinforced laminate is measured. The Barcol hardness tester is used to determine the extent of cure of a laminate. This is measured in mPa.
C-glass fibre surface tissue (surface veil)
This is a very thin layer of glass. When used on the outside of a laminate it gives a fine surface finish and gives added chemical resistance to the laminate.
Catalyst
A compound called MEKP (Methyl Ethyl Ketone Peroxide) which is added to the liquid resin and causes a chemical reaction to take place. The resin is thereby transformed into a solid.
NOTE: CARE SHOULD BE TAKEN NOT TO MIX CATALYST AND ACCELERATOR DIRECTLY, SINCE THESE MAY REACT VIOLENTLY.
Chopped strand mat
This is the mat of glass fibre (chopped fibre) bonded at random with a binder and used to manufacture the liner.
Cure
This is the process of hardening the resin. It occurs when catalyst and accelerator are added to the resin. Pools lined with glass fibre must be left to cure for ± 6 days before filling with water.
Flow coat (topcoat)
This is the final layer of resin that provides chemical resistance and a smooth surface finish. It contains liquid wax, which migrates to the surface when the flow coat cures and causes the flow coat to have a tack-free surface.
Gel-time
The time taken between the additions of the catalyst to the resin, to that stage where the resin becomes jelly-like and cannot be used anymore (normally in the region of 15-30 minutes).
Isopthalic resin
A certain type of polyester resin, which has good chemical resistance and superior water-resistant properties.
Laminate
This is a layer containing glass fibre reinforcement (chopped strand mat) and resin in the hardened state.
Orthopthalic resin
It is a general-purpose polyester resin. It has a lower strength than the isophthalic
polyester resin and lower chemical and water resistance. This type of resin is not
suitable for the lining of pools.
Pigment
This normally refers to a colour additive (known as pigment paste) with which the flow coat is normally coloured. Any desirable colour can be obtained, but cannot be
guaranteed.
N.B. Dark-coloured pigment pastes are not recommended for the lining applications.
Pre-accelerated resin
It already contains accelerator, so that the user only has to add catalyst. This eliminates the danger of catalyst and accelerator coming into direct contact. All pool resins and pool coats /flow coats are factory accelerated.
Primer
This is the first layer of resin that is applied when lining a pool. It is a very liquid resin (low viscosity) which penetrates the concrete and allows subsequent layers of glass and resin to bond to it.
Rovings
These are strands of glass reinforcement manufactured for filament winding / chopper-gun applications (known as continuous roving).
Seal Coat
See “Primer”.
Styrene Monomer
This is the solvent in the polyester resin. It is sometimes used to reduce the viscosity of polyester resins. Styrene monomer keeps resin in a liquid form until such time as a catalyst / hardener is added.
Thixotropic additive
This additive increases the viscosity of polyester resins so that they can be used on vertical surfaces without running down. All pool laminating resins and pool coats / flow coats contain this additive (called aerosil or cabosil).
UV-resistance
Polyester resins have a tendency to start yellowing in sunlight. Resistance to this yellowing is called UV-resistance. It can be achieved by the addition of UV-resistant additives. (Tinuvin is one of the common U.V. stabilizers used).
Waxed resins, wax-free resins
In order for a resin to cure properly in air, it contains wax. This migrates to the surface and forms an air barrier that allows the resin to cure. Hence a waxed resin has a waxed surface when it has cured. In order to apply subsequent layers of resin and glass, this wax layer must be removed (normally by sanding).
PREPARATION
Removal of paint and contamination
If the pool has previously been painted, then all paint must be removed first. This can be achieved in a number of ways, e.g. sandblasting, wire brush, sanding or paint removers. All contamination (such as algae or oily deposits) must also be removed, so that the pool is clean and free of any residue.
Remember: Surface preparation is the key to a successful glass fibre lining.
Inspection and repairs
After cleaning, the pool should be inspected for defects such as cracks, leaks, crumbling plaster etc. All such defects must be repaired fully before work continues. Repairs can be done using cement grout or a polyester resin/filler mixture. Once cured and allowed to dry, the repaired area must be sanded flush with the surrounding surface.
In the case where the pool is extensively cracked, the cause of such cracking may be earth movement. In such cases a full-scale repair must be affected, such that the structural strength of the pool is the same as it was originally.
Failure to do such a repair may result in failure of the lining. Proper repairs are essential to the long-term performance of the liner thus particular attention should be given to this aspect.
Filleting of corners
All corners (wall-wall, wall-floor and steps) must be filled with cement grout and filleted to give a radius of at least 50 mm. This allows for easier application of the liner and an improved liner to pool surface bond in these areas.
Removal of the coping stones and mosaics
It is strongly recommended that the copingstones and mosaics be removed. This allows for the liner to be carried under the copingstones and mosaics and results in a more reliable bond between liner and pool surface. Further it prevents water seepage behind the liner.
Once the copingstones and mosaics have been removed, these areas must be cleaned thoroughly.
The replacement of the coping stones and mosaics after installation of pool lining is discussed in Section 7.
Special considerations if the coping stones and mosaics are not removed
If the coping stones are not removed for some reason, then a groove must be cut as high above the water level as possible to secure the liner. This groove should preferably be of dovetail shape and should not be less than 20 mm deep x 10 mm wide. The liner must then be secured into this groove during application (See Section 5.5).
Final wash
Once all repairs and filleting have dried completely and have been sanded flush, the acid wash can commence. For old pools it is recommended that a 1% hydrochloric acid solution be used to wash all areas of the pool surface. For pools with new concrete or plaster, a 5% HCI solution should be used. The purpose of the acid wash is to neutralise alkalinity in the concrete.
Upon drying, the pool must be washed thoroughly with clean water and then allowed to dry completely. Polyester resin will not adhere to the pool surface if it is not completely dry, thus the long-term performance of the liner will be compromised if this is the case.
NOTE: When doing an acid wash, it is recommended that safety goggles and rubber gloves be worn to protect the eyes and hands. Suitable protective clothing is also beneficial.
APPLICATION OF THE PRIMER
Selection of the primer
To ensure a good bond between the GRP liner and the concrete surface of the pool, a primer or seal coat must be applied first. The resin used should be a wax-free, thixotropic isophthalic polyester resin.
NOTE: A general purpose or orthophthalic polyester resin must not be used since this has poorer environmental resistance than the isophthalic type. The resin should be selected after consultation with the resin supplier.
It is also recommended that pre-accelerated resin be used for safety reasons (so that there is no possibility of catalyst and accelerator coming into direct contact).
Application
The surface area of the pool must be determined and sufficient resin prepared, to be able to coat the surface at a rate of + 200 g/m2. The resin must then be split into batches small enough to be applied prior to gellation of the resin. (The manufacturer’s data sheet should be consulted in this regard). Each batch of resin must then be catalysed before it is required.
WARNING: If an unaccelerated resin is used, care must be taken not to mix catalyst and accelerator directly, since a violent reaction can occur.
The resin must be applied at approximately 200 g/m2 to the pool surface using either paintbrushes or lambs wool rollers.
Application of primer coat to take place in conjunction with the application of the liner.
APPLICATION OF THE LINER
Selection of resin
A good quality wax-free, isophthalic resin should be selected after consulting with the resin supplier. A thixotropic additive is useful to prevent the resin from flowing down the vertical walls of the pool. A pre-accelerated resin is preferred for safety reasons. Note that here again, a general purpose or orthophthalic resin must not be used, as this will affect the quality of the liner.
Selection of glass fibre reinforcement
It is recommended that chopped strand mat be used. Only 450 g/m2 types are acceptable. A fine C-glass fibre surface tissue is also required for finishing purposes.
A new stitched chopped strand mat is now available. The new product has a surface tissue already stitched to a 450 g/m2 stitched mat. This product can be applied in one single lay-up.
Amount of material required
At this stage an assessment of the requirements for the liner should be made. The following recommendations are made:
Cosmetic linings: For pools in very good condition in stable ground, the minimum amount of glass fibre that can be used is a single layer of the 450 g/m2 type. A surface tissue must always be used.
Lining of a leaking pool: For pools that have required some repair work (indicating that the pool was at some stage subject to high stress) but are otherwise in reasonable condition, the minimum amount of glass fibre mat that can be used is two layers of 300 g/m2 (i.e. 600 g/m2). The resin/glass ratio should be 3:1 by mass (i.e. 25% glass content by mass). Once the reinforcement has been selected, the actual amount required should be calculated as follows:
Mass of glass fibre mat = glass mass per m2 pool surface area, e.g. 450 g/m2 glass fibre x m2 = glass weight
Mass of resin required = total glass mass x 4 (includes primer coat) e.g. glass weight x 4 = resin weight
Surface veil area = pool surface area
All of these amounts should be increased by 10% to allow for waste.
Application of the liner
The pool must be divided into several sections, each of which can be easily laminated well within the expected gelling time of the resin. Note that the gel time of the resin is dependent upon the prevailing temperature (surrounding air and concrete) and the amount of catalyst (and accelerator) used. The catalyst content (and accelerator content if resin is not pre-accelerated) can be varied to alter the gel time at different temperatures. The manufacturer’s recommendations in this regard must be followed at all times.
The fibreglass mat must be cut and trimmed to fit one of the sections and then weighed (or the mass calculated). The correct amount of resin (resin mass = 3*glass mass) must be weighed and catalysed (accelerate if necessary). Where the copingstones and mosaics have been removed, application of the liner must start at the location of the copingstones and progress down the wall towards the floor. About 80% of the resin should be applied evenly to the pool surface, followed by the glass mat.
The glass mat must then be rolled with a metal roller to ensure consolidation of the laminate and removal of voids. Additional resin can now be applied to obvious dry spots and these must be worked on to ensure full wet out of the fibres. The next layer (if required) is applied in the same manner before the first layer starts gelling. This is followed by the C-glass surface veil that must also be thoroughly wet out with resin.
(Applied using the wet on wet technique).
The next section can then be started and is done in the same way as described above. The glass mat should be overlaid between sections by a minimum of 50 mm for wall to wall (and floor to floor sections).
Once the walls have been completed, the liner is applied to the floor, also in sections. Care must be taken to keep the working area clean and no walking must take place on the uncured liner. Floor to wall joints should be overlaid by a minimum of 200 mm.
The steps should be lined last and an additional layer of glass fibre mat must be applied here. Again any joints must be overlaid by at least 50 mm.
Additional layer of 450 g CSM to be applied to top perimeter of pool, including step
edges (min. 150 mm wide).
Special considerations for the case where the coping stones are not removed
The groove cut for securing the laminate must first be covered with large quantities of resin. The mat must then be laid into the groove and worked to ensure complete wet out. Additional resin must then be applied. At least 5 rovings (60 ends) must then be inserted longitudinally into the groove and wet out with resin. The groove must then be sealed with a mixture of resin and silica powder. The ratio of powder to resin should be such that the viscosity is high enough to prevent flow. Special care must be taken to ensure that full sealing is obtained.
FINISHING
Inspection and repair
The liner should be allowed to cure before inspection. It must be thoroughly inspected for irregularities, dry spots, exposed fibres, etc.
Tissue mosaics must first be applied before the topcoat is applied. If it is in order, the topcoat may be applied.
Selection of top coat resin (flow coat)
The resin used for the topcoat must be a waxed isophthalic polyester (flow coat). It is suggested that this resin be pigmented to either a white or pale blue colour. The resin should be selected after consultation with the resin supplier. The topcoat / flow coat is factory pigmented white or pool blue.
Application of top coat
The resin should be catalysed (and accelerated if necessary) to give a reasonable gelling time at the prevailing temperature. The resin must then be mixed thoroughly to ensure even catalyst distribution. Application of the topcoat must be such that a minimum coverage of 400 g/m2 is obtained, depending on manufacturer’s specifications. Paintbrushes or lambs wool rollers can be used to apply the topcoat.
5.4 Inspection and repair of the topcoat
The topcoat must be allowed to cure fully (inspection may take place once the topcoat has obtained a tack-free surface). Should defects be identified during inspection, the defective area must be sanded down to remove the wax surface. The area should then be washed with styrene and painted over with flow coat.
5.5 Time allowed for cure
Before filling the pool with water, the liner and topcoat must be given sufficient time to cure completely. If this is not done, the liner will be more susceptible to moisture attack, debonding and cracking. In winter 5-6 days should be allowed between completion of the pool and filling with water and in summer a minimum of 3 days. No fibreglass should be applied when temperatures are lower than 10° C
REPLACEMENT OF COPING STONE AND MOSAICS
If the coping stones were removed during construction of the liner, they can now be replaced after the topcoat has cured completely.
GENERAL CONSIDERATIONS
Construction of a swimming pool liner should not be started if there is a possibility of rain, since each process (priming, laminating and finishing) should be continuous until completed. If insufficient time is available to allow completion of a particular step, it should not be started.
However, if it has not been completed in one session, the wax at the edge where the laminating was stopped must be removed by means of sanding, and then styrene washed to create a tacky surface.
It is recommended that no work should take place in an air temperature lower than 10° C.
Always follow resin manufacturers recommendations on the use of resins
Always use safety goggles and a face mask when sanding fibreglass
It is advisable to use pre-accelerated resins since this prevents the possibility of catalyst and accelerator coming into direct contact with each other (catalyst and accelerator may react violently).
If any materials are stored on site for a few days or overnight, they should be stored in a dry, cool area. Wet glass must not be used for laminating the liner
The finished liner should be smooth, all sharp edges must be sanded properly, and there must not be any exposed fibres or sharp edges
The pH-value of the water should be maintained between 7.0 and 7.2 at all times. Pool care additives such as chlorine and acid should always be added in diluted form.
START-UP & MAINTENANCE
Water is to be analysed professionally (authorised pool shop) and recommended water treatment to be followed. Besides standard chemicals, plastered pools will always require calcium, and in case of borehole water a metal remover is to be added if required.
Plastered pools to be brushed and backwashed daily for 3 weeks, including standard cleaning of weir and pump baskets. Fibreglass pools to be backwashed on start up and thereafter weekly.
It is recommended that an automatic pool cleaner not be installed immediately. Refer to the interior surface manufacturer’s recommendations.
After 3 weeks salt for chlorinator may be introduced.
For optimum results of a good-looking pool surface, pool has to be regularly and correctly chemically treated and generally maintained. Quarterly water test by authorised pool shop is recommended.
