Here’s an article to give us an idea of the background of spray on concrete and some crucial details we need to know before ordering such process for our project. The mechanism of spray on concrete has been applied for about 70 years, most especially when it comes to civil engineering applications, such as roads, roadway repairs and tunnels, and in commercial projects. The widely known residential uses are swimming pools and foundation repair. In rare cases, it has been used for basement foundations.
Simplicity of Work
The needed tools and concrete mix ingredients are available in any huge construction equipment retailer and concrete supplier. Interior ground pool contractors frequently have shotcrete installers, or known qualified contractors in the area. But, there are lots of contractors who are not skillful when it comes to spray concrete especially during house build-up.
Codes are not mainly restricting the process of concrete installation, but rather the specifications of the concrete and its finished properties. Officials in your local town may not know or at ease with this technology. Spray concrete attend to the following ASTM standards: C1480-00 Standard Specification for Packaged, Pre-Blended, Dry, Combined Materials for Use in Wet or Dry Shotcrete Application, C1436-99 Standard Specification for Materials for Shotcrete, C1398-98e1 Standard Test Method for Laboratory Determination of the Time Setting of Hydraulic-Cement Mortars Containing Additives for Shotcrete by the Use of Gillmore Needles, C1141-01 Standard Specification for Admixtures for Shotcrete and C1385-98 Standard Practice for Sampling Materials for Shotcrete.
Spray on concrete process needs unique equipment and skilled workers. Since the concrete is sprayed onto a surface to which it remains, any formwork needed to produce this surface will be one-sided. Lots of alternatives for the surface can be applied like in civil engineering applications; it is often earth or bedrock. Spray concrete can be applied directly to earth for a house base, although control normally can be achieved better with a formed surface.
The pre-mixed dry or damp materials in the dry process are placed into the delivery equipment. Compressed air quickly moves the materials via a hose to the nozzle, at which point the quantity of water is increase and controlled by the operator. Mixing concrete completely happens when it reaches the surface to where it applies. On the other hand, the wet process receives pre-mixed concrete in the delivery equipment, which is pumped to the nozzle, where compressed air is presented to push the material out of the hose and into what surface you’re aiming at. Either of these methods being applied, the blow of high-speed concrete against the target surface will results in the rebound of an important part of the material, normally ranges between 10 to 15% by volume. This rebounding process can be reclaimed/reused if you follow the gunner / nozzle man, and shoveling or vacuuming up the rebound. But, this extra labor will add to the expense of using spray concrete.
Normally, ¾” plywood are forms for flat surfaces or shallow curves and two layers of 3/8″ plywood are being utilized to produce tighter radius curves. In installing basement wall against the ground, a drainage mat is pinned against the soil and then applies a waterproof membrane and reinforcement.
The reinforcement must be very stable in order to prevent its rattling under the impact of the concrete. If the reinforcement is not sufficiently restrained, it will produce voids in the concrete around the rebar because of its vibration. Durable bars are usually safe to form or to rebar partially embedded in previously set concrete. The rebar must be kept back at the right distance off the backing by using periodic supports. Lastly, wires should be tightly strung across the form at about 2′ on center at the finish surface level, to guide the installer in keeping the concrete thick, to give a screeding plane, and to permit construction of accurate outside corners. After completing the screeding, the wires are being removed.
Even though the concrete is still wet, you can trowelled the surface smoothly. Most of the time, stucco is being utilized as a finish surface. When a level and true surface is needed, it should be on the side of the removable form. If the finished surface is in the inside, this requires application from the outside. There are also some concerns regarding shrinkage and cracking so the surface must be correctly protected to allow for curing. For curing, sprayed compounds may compromise adhesion so it should be avoided if the surface is later to be tiled or otherwise faced. In this case, the usual concrete curing methods should be used, like covering with misted blankets.
The advantages of concrete construction are shared by spray on concrete process, including strength, impact and fire resistance, insect and rot protection, longevity, and durability. One feature of sprayed concrete is low permeability. In addition, spray on concrete process allows the application of concrete in hard to locate areas that may not be possible to use the traditional formed poured-in-place methods.
The spray on concrete method needs minimal formwork than poured-in-place (or no formwork if applied against a suitable excavated surface), and so lowering material costs and form set-up time. Forms do not require enduring the huge pressures that needed with poured concrete. Savings in forms can be made up for higher labor and equipment costs in a spray on concrete project.