LAYING CEMENT WITH AN AIRGUN
It is after this same fashion that the cement gun is used to project cement against wire reenforcement to form walls of buildings. Carl E. Akeley was led to the invention of the cement gun by his efforts to find an expeditious and economical method of mounting specimens of large animals for the Field Museum in Chicago. He constructed a pneumatic device for spraying cement and water upon a canvas-covered framework, thus building up a body upon which the skin of the animal could be mounted. This machine was improved and tried out successfully, on a large scale, in constructing buildings.
The machine as now constructed consists of a hopper into which a proper mix of sand and cement is introduced. Compressed air blows this mixture out of a nozzle. Here it meets a jet of water also propelled by compressed air. The water, sand, and cement combine and strike the wall or surface to be coated with such an impact as to make a compact fine-grained coating known to the trade as “gunite.”
Large surfaces can be painted much more readily and more evenly with compressed air than with a brush. A widely spreading air jet is used which draws the paint out of a receptacle, breaking it up into minute droplets that are projected as a mist against the surface, covering it with a uniform coating.