What is Gunite and Shotcrete?
Anyone that works with Gunite gets used to the question “What is Gunite?” because we hear it every few days. In many cases the person that asks the question is more puzzled after hearing the answer. It’s so unique and different that it’s difficult to give a short and clear explanation. Here is some history.
Gunite (/ˈgənīt/), was invented in 1907 by American taxidermist Carl Akeley to repair the crumbling facade of the Field Columbian Museum in Chicago (the old Palace of Fine Arts from the World’s Columbian Exposition). He used a method of blowing dry material out of a hose with compressed air while injecting water at the nozzle as it was released. Instead of plaster, a cement and sand mortar was used. The results were outstanding. The technique was introduced to the construction industry as a method to patch deteriorated concrete. In 1911, patents were granted for the “Cement Gun” which is what the apparatus was called and for “Gunite” the material produced by the process.
In 1915, an Allentown, Pennsylvania business man named S.W. Traylor recognized the market for the new invention. He bought the rights and formed the Cement Gun Company of Allentown, PA, to both build the machines and do the Gunite construction work. The term “Gunite” became the registered trademark of Allentown Equipment. Other manufacturers were thus compelled to use other terminology to describe the process such as shotcrete, pneumatic concrete, guncrete, etc.
As time passed the many uses of Gunite came to light. It was ideal for creating thin but strong concrete linings and coatings. It was easy to create curves and special shapes in concrete. Bridges, dams, reservoirs, pools, tanks, canals, docks, slopes, tunnels, pipelines and the like all became candidates for Gunite. Further, steel producers, experimented with patching firebrick using Gunite with remarkable results. The patches were easy to install and long lasting. Eventually, firebrick linings became obsolete replaced with Gunite concrete which was less expensive, quicker to install and lasted longer.
In the 1930’s, the term “Shotcrete” was coined by the American Railway Engineering Association to describe the process. Later, in 1951, the American Concrete Institute adopted the term shotcrete to describe the “dry mix” process known as Guniting. The term shotcrete is now also used to describe the “wet mix” process that was developed during the 1950’s as an alternative to Gunite.
Gunite is then the trademarked term for the material produced by the “dry mix” shotcrete process. There are two types of shotcrete, “wet mix” and “dry mix” as defined by the American Concrete Institute.
Despite the advances in materials used for Gunite, the process remains unchanged to this day. It is generally accepted that the quality of Gunite depends solely on the experience and skill of the artist. Unfortunately, we occasionally run into people who have had a bad experience with Gunite, most always traceable to lack of skill. That is why it is so critically important to use a gunite contractor such as Modern Method Gunite that has carefully developed and retained the top artisan talent.
Gunite remained a proprietary trademark until 1971 when it became part of the English language. Webster’s Dictionary defines Gunite in the following way; Gun·ite \ trademark used for a mixture of cement, sand and water sprayed onto a metal mold.