Fibreglass Pools


- have been around for a long time - well over half a century - so they are not new technology and most of the problems associated with this type of pool were identified, and solved, long ago. 

Nevertheless, there are several issues that apply only to fibreglass pools and these should be carefully noted to avoid damage to the structure, finish and general good-looks of the pool. They are also known as Glass-Reinforced-Plastic, or GRP, pools


Fibreglass pools are moulded using resin and glass fibres, usually pre-formed over a reinforcing structure of stiffening 'ribs', and finished with a Gel Coat - an impermeable, non-porous coloured top layer that is typically 30 mils (thousandths of an inch) or 0.75mm thick. You might think that this is a little too thin but any thicker than that and the Gel Coat would be more prone to cracking 

OK, now we make it level and add water!  

Water level

Maintain the water level halfway up the entrance to the skimmer for the most efficient operation of pump, skimmer and filter

Draining the pool

Fibreglass pools are designed to be kept full of water, they have been installed and the space between the outside of the pool and the inside of the excavation have been back-filled. The pressure of water inside the pool counteracts the pressure of the backfilled soil and aggregate and any ground water that accumulates on the outside of the pool shell. Thus there is no strain on the shell of the pool

Do not drain your fibreglass pool until you have spoken with either the original installer or the manufacturer for their professional advice.  If the pool is drained there is a possibility that ground pressure (hydrostatic pressure) could force the sides of the pool inwards, causing it to distort, buckle or even crack

Additionally, if there is ground water present (around the outside of the pool) an emptied fibreglass pool can easily float up out of the ground. Getting it back down again requires complete removal of the pool-shell and re-excavation of the hole

Pool surface care

It's only the Gel Coat that is visible and that's the part that has to be cared for. All pools get a 'bathtub ring' at the waterline from body oils, suntan creams and lotions, etc., and fibreglass pools are no exception. This ring can be removed without effort by using pool tile cleaner, available from your local pool shop. Do not use any abrasive tools or products as these will damage the Gel Coat and, at the very least, take the shine off

If the Gel Coat loses its shine and becomes dull it can be brought back to life using a colour restorer polishing product as used in the automotive trade. T-cut is one brand and there are many others. After buffing the surface back to its original shine a coat of wax should be applied to protect the surface

Fibreglass pool tools

Like most shiny surfaces, Gel Coat can be scratched. Ensure that the tools you buy to clean your pool are correct for fibreglass pools. The heavy vacuum head used in a tiled pool, for instance, will damage the surface of a fibreglass pool. Your local pool shop will have the correct tools - so you can clean the pool without damaging it

Surface cracking and crazing

It is not uncommon for hairline cracks to appear in a fibreglass pool. The cracks only affect the Gel Coat and do not penetrate to the structure of the pool, nor do they cause leaks. Hairline cracks can be repaired by a specialist but they will probably reappear at some point in the future

Pool Chemistry

Correct procedures for care and maintenance of a fibreglass pool will extend its life.  Follow these simple rules to get the best results

Control the Water Balance and keep values within these parameters: -

pH  7.2 - 7.6 - Free Chlorine 1 - 3 ppm - Total Alkalinity 60 - 100 ppm - Calcium Hardness 250 - 350 ppm

pH  - Do not allow the pH to fall below 7.0 as the water will then be acidic and cause the Gel Coat to age prematurely. Also, do not allow the pH to rise above 7.8 as lime-scale may appear in the least turbulent areas of the pool

Free Chlorine - The main culprit for causing fading is the Chlorine used to sanitize the pool. High concentrations of Chlorine will attack the Gel Coat and bleach the colour from it. It will age prematurely and may deteriorate swiftly. For this reason, Chlorine should never be allowed to come into contact with the surface of a fibreglass pool in a concentrated state.  Chlorine should be applied with the pump/filter running. Application varies according to the form of Chlorine being used: -

Granulated Chlorine - dissolve in water before trickling it into the skimmer with the pump running, and NEVER throw it directly into the pool. It will bleach the surface at the point of contact

Chlorine Tablets - should be placed in a feeder. NEVER throw them into the pool as they will bleach the surface of the pool at the point of contact, leaving unsightly circular, bleached patches

Liquid Chlorine (Sodium Hypochlorite) - should be poured into the pool at the jets with the pump/filter running. This ensures rapid dilution and dispersion of the sanitizer

Note: -H²O² - Hydrogen Peroxide sanitation , coupled with a UV Ionizer is a very good system for a GRP pool and will mean that you neverhave to put chlorine in the pool

Leave the pump running for 4 hours after adding chemicals


  • No need to resurface, or replace liners, or re-grout, or replace missing tiles
  • Fast installation; typically 2 - 4 weeks but can be less
  • Smooth surfaces make for easier cleaning
  • Unlikely to sustain damage due to ground heave or minor earthquakes
  • Less chemicals needed to maintain the pool
  • If installed above-ground may not need planning permission - check before you buy!


  • Costly to install when compared to some other types of pools
  • Limited sizes and shapes
  • Too shallow for diving
  • Colours fade over time, especially the darker shades
  • Cannot be drained for maintenance

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Ken Walker - MyPoolGuru©