Sprayed Concrete

The Gunite Technique...

Gunite is the ''dry spray'' method of spraying concrete, widely regarded as a leading method of construction for high quality, luxury swimming pools.

The Shotcrete Technique...

Shotcrete is the ''wet spray'' method of spraying concrete, whereby the concrete is delivered to site in convenient, ready mix lorries.

Guncast is a market leader in this field. See details of the process and its benefits below.

  • Excavation

     

    In most cases, the excavation is carried out with the banks of the excavation battered back to provide a safe working zone for the pool construction team.

    A sub-base of 150mm, 50mm shingle is laid to the base of the excavation to provide a firm foundation and drainage under the pool. The shingle is then capped with 50mm lean mix to provide a clean and level base for the pool construction.

    Sprayed concrete is typically built up in layers so it has its own inherent strength, therefore a light weight back shutter is all that is needed to enable reinforcing to take place.

  • Reinforcement

     

    Steel reinforcement is fixed throughout, which is in accordance with current British Standards and designed by qualified structural engineers. For most residential pools, 2 layers of 10mm high tensile steel fixed at 200mm centres in both directions satisfies engineering standards. Design calculations can be provided for examination by Local Authorities or other interested parties.

  • Gunite

     

    Gunite is small aggregate and cement which is mechanically mixed together and fed in a dry state into the hopper of a "gun". This is then metered by a rotating barrel into the delivery hose where the mixture is forced by air supplied by a 600cfm compressor to the nozzle. At this point water is added and the wet mixture sprayed at high velocity on to the shuttering and reinforcement.

  • Shotcrete

     

    Shotcrete is a high cement content, small aggregate ready mix concrete fed through a specialised concrete pump and small bore delivery hose (2inch). It is aerated at the nozzle using a 200cfm compressor. The concrete is then projected at velocity onto the shuttering and reinforcement.

  • Spraying

     

    The most satisfactory structural design incorporates a cove at the wall to floor junction. If necessary, a 90° detail can be incorporated.

    The walls are gunned in sections to full height and thickness. When the walls are complete the central portion of the floor is gunned.

    The thickness of the applied concrete is determined by wires stretched across the face of the work to the required finished levels.

    Final finishing of the concrete is achieved by cutting down the concrete surface with long handled, large steel trowels.

  • Personnel

     

    The Gunning Crew:

    Nozzleman - Most skilled operative, responsible for placing the concrete and controlling its hydration (hydration controlled on Gunite method only).

    Gunman - Regulates the supply of the mix and the air from the gun.

    Mixer Operator - Ensures the sand and cement are correctly proportioned and of good quality (Gunite method only, Shotcrete is pre-mixed).

    Labourer(s) - General labouring help

  • Advantages and Properties of sprayed pool shells

     

    1 - The method of construction complies in all respects with BS EN 1992. Structural calculations can be provided to satisfy Local Authority requirements.

    2 - High speed of construction.

    3 - The shell is monolithic with no joints that can be subject to cracking through movements.

    4 - For larger pools, where reinforced concrete would be used, a sprayed pool would almost certainly be a cheaper alternative.

    5 - Difficult access sites require only a 50mm diameter hose to reach the working area, which can be up to 80 metres away from the plant and materials.

    Properties & Advantages of Gunite



    28 Day Strength - usually specified as 35 N/mm² although strengths of 70 N/mm² are frequently reported.

    Drying shrinkage - 0.06 - 0.10%

    Water / cement ratio - 0.35 : 0.50 by weight

    Ideal for pools with intricate shaping.

    Properties & Advantages of Shotcrete



    28 Day Strength - usually specified as 35 N/mm² although strengths of 40 N/mm² are frequently reported.

    An extremely quick construction method which is typically used on larger pools, where speed is of the essence.

TYPICAL CALCULATIONS

Typical Calculation | Example 1

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Typical Calculation | Example 2

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Typical Structural Drawing 1

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Typical Structural Drawing 2

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