Fibreglass Pools and Pond Lining
It is provocative to say the glass fibre and polyester resin (glass reinforced plastic = GRP) is as easy to apply as wall paper. Given the correct materials and the proper preparation and advice - it is no more difficult. Should you have the pond professionally built and GRP lined ensure that the firm carrying out the work has wide experience of pond construction as opposed to general glass fibre work. At the very least they must be fully aware of the toxic effects of solvents and chemicals on fish and therefore the absolute necessity of proper curing (hardening) of the laminate and topcoat system.
Glass fibre is an excellent and very suitable material for use in lining fish ponds. It is resistant to weathering and temperature variations and provides a water tight, smooth and easy to clean surface. These instructions are primarily concerned with the materials that should be used and the application of the glass fibre.
Type of structure:
It is important that the structure, which is to be lined with GRP, is capable of withstanding the soil and water pressure in its own right. Whilst the glass fibre will naturally add to the strength and rigidity it is not, in this case, being used for this purpose. Normally the pool is constructed from brick, lightweight block or concrete block. With the exception of brick built ponds, it is necessary for a cement render to be applied and for sufficient time to be allowed for it to dry. Bear in mind that a half inch cement render should be kept damp for 3 days. A further 10 days should be allowed, at reasonable temperatures and dry conditions, before it will be possible to apply the G4 primer coat.
There are many formulations of polyester resin but all contain around 35% styrene monomer which can, unless the laminate is properly cured or hardened, have a toxic effect on fish. However the fact that there are many GRP lined ponds, including the ready made ones, means that providing the correct materials and methods are followed a GRP lining is non toxic to fish. There are two types of polyester resin that are used. One is a general purpose - pre-accelerated resin with a slight thixotropy to enable it to "hold up" on vertical surfaces and the other a highly thixotropic resin - referred to as a Gelcoat - both of which, as stated earlier, contain styrene monomer. Most general purpose resins contain some amine - 0.1 to 0.2% (by weight) but this is required for the proper curing of the resin, although it is considered toxic to fish.
Gel Coat- Topcoat:
A high quality Lloyds approved isothallic & thixotropic gel coat resin with excellent weather resistance also known as "Resin B". Gel coat forms the smooth outer surface of the finished laminate and therefore is usually applied to the prepared mould first but cannot be used to coat a finished laminate without the addition of wax solution which makes the gelcoat into flowcoat. Flow coat is applied after the laminate, as in sheathing fish ponds but to use as a flow coat a wax solution must first be thoroughly stirred into the gel coat at 2% by weight (20ml per kilo) to eliminate surface tackiness. Activated by catalyst added to the gel coat at 2% by weight, minimum. Working time at 20°C is approximately 20 minutes. Supplied clear or white, pigment colour pastes can be added.
Pigments for GRP:
The usual colours for ponds, particularly Koi ponds, are either black or British Racing Green since Koi show up particularly well against dark colours. It is possible to pigment Topcoat in a wide range of colours. This is done by using polyester pigments specially made for polyester resins with a saturated resin that will not harden on its own. No more than 10% of pigment by weight should be added but in practice because dark colours have high opacity it is unnecessary to add this amount. British Racing Green does contain some lead, 4.6%, of which 0.4% is soluble lead. However since this is locked into the Topcoat system it is safe as water will not leach out the lead. To further dispel any concerns we know that British Racing Green has been used as a topcoat colour by several of the leading Koi stockists in the country.
How to do it:
There is no need to laminate the whole pond at one time, as some think, it can be done in stages providing each stage is left in the correct state for the next to be applied.
Order your materials:
Your supplier needs to know the surface area either in square feet or square metres that are to be coated. Everything required can be worked out from that figure. Should you wish to work it out for yourself then it is straight forward - all you have to know is:-The weight of the glass fibre that you will be using, normally 450gm per sq/m, and that the resin usage is 2.5 times the weight of the glass fibre.
For example a sq/m of 450gm glass fibre mat will use approximately 1.13kg of polyester resin. (450gms x2.5 = 1.125kgs). It is unlikely that you will use less and depending on your expertise it might be a little more - allow say 5% for wastage. For the Topcoat a consumption of 400gms per sq/m can be used with a 10% maximum, by weight, addition of pigment. Apart from the catalyst and the G4 Primer Sealer, the only additional costs are for tools and cleaning materials. A typical list of materials is given at the end.
The GRP Laminate:
In our experience two layers of 450gm/sq metre glass fibre mat is the minimum. A two layer laminate will provide a thickness of around 2mm. Anything less is asking for problems! Under ideal laminating conditions one layer of glass fibre mat can provide a non-porous laminate but under practical conditions it is highly unlikely it will do so. This is due to the consideration that the glass fibre is being applied to rendered surfaces and with few exceptions there will be exposed aggregate or sharp particles of cement render projecting above the surface that can penetrate easily through a single layer causing a hole and possible leak. The other consideration is that with one layer it is also possible to have "dry areas" or areas that are not sufficiently saturated "wetted out" with resin. By using two layers this risk is reduced by 200% since the second layer is consolidated into the first and the risk of voids is substantially reduced. Three layers is the optimum but normally two are satisfactory.
Working temperatures/ Curing times:
There are two principal influences on the working and curing times of polyester resins - the quantity of catalyst added and the ambient temperature. The more catalyst added the shorter the working time and the quicker the cure "hardening". Polyester resins do not cure properly (unless specially treated) at low temperatures (below 10°C) or high humidity. More of a potential disaster is rain as this can spoil a laminate, while still wet, so it is necessary to watch the weather and if at all suspect make provision for protecting the laminate during the early stages of its cure. It is not advised that GRP work is carried out below 15°C although the preferred temperature would be 18°C. Conversely too high a temperature 25°C will cause problems with the too shorter working times of the resin.
Working times of resin:
General purpose resins are mostly pre-accelerated, requiring only the addition of the M.E.K.P. (Methyl Ethyl Ketone Peroxide) catalyst or hardener. The normal addition is between 1 and 2% by weight. Therefore for every 1000gms of resin 1% addition means adding 10 grams. This can be measured by using a catalyst dispenser, It is not advised that more than 2KGs is mixed up at a time until you have experience of the working times. The amount of catalyst can then be adjusted to suit the size of mix/working time/ambient temperature, typical catalyst addition and working times are shown below:-
Catalyst Gel Time M.E.K.P