Method of and apparatus for applying a sprayed concrete layer to a surface

An apparatus for applying a sprayed concrete layer to a surface comprising:

• a concrete feed pipe for a pumpable and sprayable concrete mixture;
• a sprayer with a compressed air connector device to which said concrete feed pipe is connected;
• a compressed air source containing compressed air at several bar;
• a powder silo for a powdery concrete additive;
• and
• a compressed air feed device connected to said compressed air source and said powder silo and to said compressed air connector device of said sprayer for metering a plurality of partial flows of said compressed air and said powdery concrete additive, said compressed air feed device including a register comprising at least two compressed air chambers which open into said compressed air feed connector and are connectable by a plurality of control valves in alternating sequence to said powder silo for loading said powdery concrete additive into said chambers or connecting said chambers to said compressed air source for blowing said partial flows of said compressed air and said powdery concrete additive through said chambers, said register containing two of said compressed air chambers, the downstream and upstream ends of each of which having one of said control valves, and between said control valves at said upstream and said downsteam ends each of said compressed air chambers being connected to said powder silo respectively by both a connecting duct having a pump and a return pipe.