Method of spray application, and spray apparatus, for bentonite material

A bentonite-based material spray method for forming a bentonite layer by spraying a bentonite-based material having as a main material thereof bentonite or a mixture containing bentonite,

• the method comprising:
• supplying compressed air to a supersonic nozzle formed with a compression portion, a constriction portion and an expansion portion, said compressed air being accelerated to supersonic speed in the process of being supplied to said expansion portion by passing through said constriction portion, and jetting the supersonic compressed air from a jet orifice formed downstream of the expansion portion;
• mixing a bentonite-based material with said compressed air, and forming a bentonite layer by wet spraying said bentonite-based material mixed with said compressed air, particle size of bentonite contained in said bentonite-based material is not larger than 10 mm, said bentonite-based material is a mixture containing said main material and a liquid;
• and
• using a material as said main material wherein a dry density correlating to the content of liquid within said bentonite-based material is equal to or greater than a predetermined dry density at the point where the content of said liquid is equal to an optimum water content of the material,
• wherein an upper limit of the content of said liquid in said bentonite-based material is set to a value greater by 4% than the optimum water content and the lower limit of the content of said liquid in said bentonite-based material is set to a value smaller by 1% than the optimum water content.