Home Detailed application Technical Detail Pond and Pool Lining - Technical Details

Pond and Pool Lining - Technical Details

General Information

GRP is widely used for the manufacture of tanks, garden pools and swimming pools. It will give an inert, hard wearing, long lasting, waterproof skin, that will withstand ground movement and allow the use of aggressive cleaning techniques without danger of damage to the lining. The technique involves the formation of a GRP laminate in situ using chopped strand mat reinforcement and suitable polyester resin and topcoat pigmented in any BS 4800 colour.

Important Considerations When Applying GRP to a Pond or Pool Lining

It is essential that only suitable resins and topcoats are used to ensure that no residual taint occurs which may affect the contents of the lining. It is also vitally important that the laminate is allowed to cure completely before it comes into contact with water. Always use summer catalyst when curing any resin or topcoat used for the lining, this gives a more consistant cure than winter catalyst and will give more predictable results.


A GRP laminate can be applied to a concrete or masonry structure. It is important that the stonework is clean, dry and fully set. Any imperfections in the structure with be telegraphed through to the finished surface and may manifest themselves as weaknesses in the finished lining.

Before the laminate can be applied any angles in the structure need to be rounded off and it must be primed with G4 PU primer.

Corner Preparation

Rounding and smoothing off the corners makes the laminate easier to lay, it reduces any points of weakness and stress on the laminate and also makes the finished lining easier to clean. Sharp angles are filleted using resin mixed with an inert filler, this can be slate dust, talk or chalk. Do not use cement or plaster as a filler, these substances are alkaline and will kill the cure if the laminate is laid on to them.

The filler is mixed at a ratio of 1 part resin to 4 parts inert filler.

When the catalysed resin filler has been mixed it can be applied to any sharp angles of the pond. A brush soaked with catalysed resin can then be used to smooth off the compound and give a finish ready to laminate.


The concrete surface should be primed with G4 primer. This is a moisture cured poyurethane coating that should be allowed to partially cure before applying the first coat of resin. If the primer is allowed to fully cure it will act as arelease agent and the GRP layer will not bond. If the primer has fully cured it will need to be reapplied.

Apply catalysed resin to the tacky PU primer. The resin may then be allowed to cure before laying down the main laminates if the structure is too large to line in one session.

Firstly, all of the areas of highest stress should be bandaged, this includes all sharp angles, areas that have been treated with filled resin compound and steps, etc.


It is vital to ensure that the GRP is applied to the surface without any air gaps or spaces remaining so it must be well consolidated. As with the main laminate, use a low reactivity catalyst (i.e. summer or LPT) at between 1 & 2%. Lay two 450g/m2 laminates onto the structure ensuring that they are both well consolidated. Lay the second laminate over the first while it is still uncured to increase inter-laminar adhesion. The laminate can be dressed around the perimeter pool with the use of capping stones which can be adhered to the laminate with PU adhesive, alternatively, a steel edging strip can be used. The laminate and stone structure of a pool should continue over the side of the pool and onto a flat surround to allow the laminate to be dressed over the side of the structure.

Depending on the quality of the finish required, the laminate may be finished with surface tissue and lightly abraded with medium grade sand paper when cured to ensure a smooth finish.

Pigmented topcoat can then be applied to the laminate using no more then 1-2% low reactivity catalyst. Pigment addition should be no more than 10%. Is is advisable to use only darker colours in pond applications. Where the topcoat is in permenant contact with water, 2 thin applications of topcoat can be used to give a perfect finish. The topcoat thickness should generally not exceed 0.5mm.

Always excercise caution when applying resin or topcoat in very hot weather by using LPT catalyst. Avoid applying the topcoat in very hot direct sunlight as this can lead to 'tacky' topcoat.

Dark grey topcoat pigment normally gives the best appearance in a pool.

Curing the Laminate

It is essential that the laminate is allowed to cure completely before it comes into any contact with any water. This avoids any taint of the water and 'staining' of the topcoat. The pool/pond should be kept completely dry by errecting a 'tent' or sheet over the top of the pool. In summer the sheet needn't be used when dry weather is forecast and the heat from the sun will assist the curing process. Otherwise a 1KW fan heater should be placed in the pool under the tent to heat the surface of the laminate. It is important that a fan heater is used, as the heat should be circulated over the surface.

No attempt should be made to fill the pool for two weeks after the topcoat has been applied. It is vital that the laminate is left to fully cure during this period. If the pool does get wet and 'staining' of the topcoat occurs it can be removed by 'cutting back' the laminate with T-Cut or Brasso. When this period or longer has passed the pool should be filled with a hose pipe and the water left to overflow for a period of 2 hours before the pond or pool is used. This process ensures that any surface wax or other debris is carried away with the overflowing water.


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