Construction Solutions LLC
PO Box 1334
Cedar Park, TX 78630
Shotcrete/ Gunite is a process and method of pneumatically applying cementious material to a structure. It is commonly used to build pools, as well as bridges, homes, tunnels, water tanks, retaining walls, movie sets and repair all above mentioned as well. Gunite has been in use since the early 1900's with excellent success.
Shotcrete comes in two basic forms: dry process or dry gun method and wet process
The dry gun method or dry process shotcrete (also known throughout the industry as gunite) uses a volumetric mixer truck in which concrete sand and type 1 portland cement are hydraulically mixed on site and compressed by an auger conveyor system. This mixture is then moved into a gunning machine where it is mixed with air from the air compressor and is blown though a hose by extreme pressure to the nozzle where water is added and mixed at the tip of the hose and then blown pneumatically into the rebar enforced walls and floor. Only the necessary amount of water is added for hydration resulting in superior strength over conventional concrete.
FYI: the term Gunite which is a process rather than a material is a former trademark and now a generic tern that has been recognized by the GCA (Gunite Contractor's Association), ASA (American Shotcrete Association) and the ACI (American Concrete Institute) since 1967.
The wet process, also referred to in the pool industry as "shotcrete" uses pre-mixed concrete from a batch plant and is a hot and live load and is transported via a conventional barrel mixer. This mixture is poured into a concrete pump and is pumped to a nozzle and pneumatically placed or shot onto the walls and floor of the structure via an air powered nozzle. Computers are used to control the concrete mixture by using a predifined design that can not usually be adjusted at the site (other than adding water) and must be at a consistancy to be able to flow through the hose.
(According to NSPI standards) We shoot a standard 11" to 12" continuous bond beam and regress to a minimum of 9" walls and 10" floor (or 4 inch coverage of the rebar) or to the specifications of the pool contractor.
Dry method pneumatically applied cementious material (or concrete) also known as Gunite is superior in strength to poured or redi-mix concrete for several reasons. Only the amount of water necessary for hydration is added to the concrete sand and portland cement mixture to make Gunite. There is not the excess water found in conventional poured concrete. The excess water found in poured concrete occupies space, and when it finally leaves the curing or hydration process, small voids are left behind.
So it can be said that dry method Gunite is more dense than that of poured concrete. In fact, 14 yards of gunite is equal to about 10 yards of redi mix concrete or shotcrete mix. Denseness is an important factor in the superior stregnth of gunite and its high resistance to the passage of water.