FOUR STAR GUNITE, LP

Shotcrete & Gunite
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SOME FACTORS TO CONSIDER
 
Just as in concrete mix designs, the water-to-cement materials ratio is the single most important parameter influencing the compressive strength, shrinkage and overall durability of the material.  With gunite, only the amount of water necessary for hydration is added to the sand and cement mixture.  So it can be said that gunite is more densely packed than ready-mix concrete.  In fact, 14 yards of gunite equal about 10 yards of ready-mix concrete or shotcrete mix.  Denseness is an important factor in the possibility for superior strength in gunite and its high resistance to the passage of water.   Nozzling technique is also crucial and less forgiving than ordinary ready-mix concrete.  Good technique by the nozzleman can mean the difference between a dense high-strength material or one that looks good on the finished surface but actually has underlying sand pockets, voids and poorly encased reinforcing steel in both the “dry-mix” and “wet-mix” processes.  Poor application technique will result in a higher probability of cracking and its negative ramifications.  Placement of the nozzleman is key as well.  Standing on the reinforcing steel can result in it being to shallow or too deep within the material.  This could potentially cause rust spots or cracking.

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Finished Spa
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Completed Steps, Pool, and Barstools

GUNITE

•    Gunite batches are mixed on site making the batches more mobile and versatile.  This aspect makes it easier to use in repair applications where all material will not be used or in multiple projects where travel between sites is required.  Since shotcrete has water added at the plant it begins curing immediately, and extra water must be added if the material is not used quickly enough.

•    Water amounts in gunite are controlled manually by the nozzleman, and are intended to merely hydrate the mix at the nozzle.  The result is less excess water in the material creating a denser and therefore stronger material.  This does leave more room for errors because measurements from the plant computers tend to be more accurate.

•    Gunite leaves more rebound (excess material that is mostly sand), as a result of the force and dryness of the material blown onto the surface.  This means the material is compacted more densely on the site leaving a smaller amount of pockets and voids, making the material stronger.

•    Because water content is controlled manually, gunite can be more effectively placed in vertical or overhead

SHOTCRETE

•    The main advantage of shotcrete is that more volume of it can be placed in less time than gunite.

•    Shotcrete batches are normally mixed by computer at a ready-mix plant, and are taken to the site wet (water has already been introduced).  This is intended to create an even consistency of water content in the entire batch, as well as increase consistency across multiple batches.  This should make the overall strength in all parts of the structure more uniform.  Since the batches are curing the moment they leave the plant, inconsistencies may arise from adding extra water to batches not used quickly enough.

•    With shotcrete, less rebound and dust are created during application making cleanup of the site easier.  This also makes shotcrete easier to work with in a confined area where rebound could damage property.  

•    With gunite all rebound is removed from the job site, while shotcrete is able to reintegrate some of the rebound produced into the finished structure.

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Gunite Wall

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Four Star Gunite * 11520 E. Germann Rd. * Chandler * Arizona * 85249 Phone:(480)252-6390 Fax:(480)677-3155 E-mail: fourstargunite@cox.net

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