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.
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.
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 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.
study has been submitted by a member and the British Structural
Waterproofing Association accepts no responsibility for its content.