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Sprayed concrete piled walls in basement
in central London
This central London basement was created when a mid terrace was demolished. Concrete piles were placed in the ground prior to excavation in order to retain the earth. The contractor's sprayed concrete team filled the gaps between the piles with a ‘Dry Spray’ mix of sprayed concrete. In the dry spray process compressed air is used to deliver the dry mix material and water is added at the nozzle.    
This shows the spraying operation in progress. The work is often difficult and dangerous often involves working in congested spaces. A great deal of attention has to be paid to health and safety considerations.
This shows the Dry Spray machine inside its ‘protective tent’. Bags of material are put into the hopper and a powerful compressor delivers it to the nozzle.
The piles are shown here after the concrete has been sprayed. The next stage will be to apply a cavity drainage membrane and then an inner lining to finish the walls to habitable grade.
The wet spray process lends itself to larger scale operations and can be used where a whole ready mix truck of concrete can be 'consumed' within an hour. This is good for lining entire basements with a layer of sprayed concrete of around 200mm thick.
This case study has been submitted by a member and the British Structural Waterproofing Association accepts no responsibility for its content. 

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