gunite

Gunite is a method of applying cementitious material by spraying it onto surfaces at high velocity, typically using the dry-mix variant of shotcrete. In gunite, cement and fine aggregates are batched locally as a dry mix and delivered through a hose; water is added at the nozzle to activate hydration as the material is sprayed onto the substrate. The spray forms a dense, adherent layer that can be built up in layers to the desired thickness. Wet-mix shotcrete is a related technique in which pre-mixed concrete is pumped through the hose and sprayed.

The technique relies on specialized spraying equipment and skilled crews to control mix proportions, nozzle suddenness, and layer thickness. Dry-mix (gunite) and wet-mix shotcrete differ in handling and curing characteristics, but both achieve rapid placement and strong bonding to prepared surfaces. The resulting material can be cast against irregular shapes and overhead areas, enabling complex forms and structural shells.

Common applications include construction of swimming pools, architectural features, tunnel linings, retaining walls, dam faces, and repair or rehabilitation of existing concrete. Advantages of gunite include fast placement, good surface adhesion, and the ability to build up thickness quickly with relatively limited formwork. Limitations involve the need for precise technique to avoid voids or cracks, material waste from rebound, and the importance of proper curing to control shrinkage and cracking.

Standards and guidelines for sprayed concrete are provided by organizations such as the American Concrete Institute (ACI) and ASTM International, which publish requirements for shotcrete and gunite applications.