Spraying installation (1) on a chassis (2) of a truck (3), comprising a spraying nozzle (4) at the free end of a telescopic arm (5) attached to the chassis (2) via elevation means, characterized by the telescopic arm (5) being supported in a first position (A) oriented along the length of the truck (3) and above the top of the truck, wherein the telescopic arm (5) is stowed in a horizontal transport position, and supported in at least one other, active position (B, C), whereby the telescopic arm stays in a horizontal position during the movement between said positions (A and B, C) in a space confined between the vertical planes of the two sides of the truck.