What is Gunite? | Part IV

Gunite is either a process or a product, depending on who you ask. As a process, gunite refers to the projection of a sand and cement with machinery and hoses to a spray nozzle where water is added before a wet "concrete like" material is sprayed on to a construction surface, such as a pool, bridge, retaining wall and countless other gunite-made structures.

Gunite Nozzleman on scaffolding shown with gunite hose and gunite nozzle during a gunite pool construction project.

Traditional concrete is usually poured or pumped into frames and other forms on the construction project. As a product, gunite is essentially a building material similar to concrete but really somewhat in between concrete and masonry mortar or grout. Unlike concrete, gunite does not have any large rocks, also called aggregates, and doesn't normally have any additives, such as chemicals designed to give concrete a quick setting time or early strength. Gunite is not "basically the same as regular concrete."

Gunite is very similar to masonry mortar or grout. The difference between the two is mostly in the process used to get the material on to the construction surface described above, often called material placement. Mortar, grout and gunite all contain similar ingredients, which are cement, sand and water.

"If sand and cement are conveyed through hoses dry by gunite machines and water is added at the nozzle, you would call that gunite. If sand, cement and water are pumped through hose by any wide range of pumping equipment available, you would call that grout."

Grouting equipment typically results in pouring the material at a low velocity. To further complicate things, let's say you wanted to spray a mix of sand, cement and water at a high velocity. That has a name too: "shotcrete". Gunite and shotcrete are the two most confused terms because so little separates the two.

"Simply, put Gunite involves water at the gunite nozzle; shotcrete involves water at the machine."

Now we can bring this discussion full-circle back to concrete. Some shotcrete pumps and nozzles are designed to spray a mixture containing some sizable aggregates, resulting in something like actual "sprayed concrete." Still, in these cases there still is a limit on the size of the aggregates used in the material because shotcrete nozzles cannot handle large rocks. The differences between these terms and processes doesn't have to be confusing. To beginners, the misuse of terminology in the construction industry can make it all difficult to understand. Fortunately, Gunite Subject Matter Experts (SME) are available to guide anyone getting started in the gunite industry!

--SME Reviewed Article 2023-02-11