Construction Solutions - Silo Mortar Dispensing Systems



Solution: Silo Mortar Dispensing Systems
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	Description:	With a silo mortar dispensing system, pre-blended dry mortar ingredients, including sand, pigments and admixtures, are delivered to the jobsite in 3,000 lb bulk bags. These bulk bags are then moved by forklift or boom truck lifts over a funnel-shaped silo, where they are dumped by pulling a hitch pin on the bag. Silos are available in a variety of sizes and models, and hold from 1 to 10 bulk bags. When the silo chute is opened, dry, pre-blended mortar is gravity-fed directly into the mortar mixer below. The silos eliminate heavy lifting and twisting associated with the production of materials. More Detail Mortar silos are delivered to the jobsite, and are equipped to be moved easily within minutes by a contractor's forklift as the masons move around the jobsite. The silo should be placed on level ground, downwind from the work area to avoid dust exposure. Material is loaded above the silo by means of a forklift. Material is dispensed by gravity into the contractor's mortar mixer of choice from the bottom of the silo. The amount of material dispensed by the silo can be controlled with a cut-off handle. The gravity feed is not dependent upon pressurized water hook-ups, electrical power, or gasoline motors. Therefore, no external connections are needed. The design of the silo is simple and highly efficient when dry mortar mix is being produced on site. Silos can be used whether the worksite is small or large. This system will greatly reduce the cost of labor and the amount of waste (sand, cement, paper bags). Silos can be fitted with dust curtains, screw augers, set at various heights, and can be used with any mixer available on the market. Some vendors of mortar mix will provide the mortar silo free of charge. Less Detail
	Risks Addressed:	Musculoskeletal disorders and worker fatigue due to manual materials handling and overhead work.
	How Risks are Reduced:	Cement bag handling is eliminated. Because bulk mortar bags are handled mechanically, with either a forklift or boom truck lift, there is no need to manually lift or carry heavy bags of cement. Masons will not need to lift or carry the 94 lb cement bags, thereby reducing the risk for developing musculoskeletal disorders of the back or shoulders. Sand shoveling is eliminated. Because the bulk mortar producer pre-blends all dry ingredients including sand, shoveling is eliminated from the mortar mixing process. Therefore, masons will avoid awkward postures of the back, neck, and upper extremities. In addition, repetition and stressful hand and wrist activities required by the mason to manually shovel material will be eliminated. Quality of Evidence Manufacturers, vendors, or worksites have reported a risk reduction. Safety and health experts believe there is a risk reduction. Manufacturers of silo systems claim that heavy lifting, and awkward and forceful hand exertions are eliminated because all the bags are handled mechanically. There have not been independent published studies measuring the effect of a mortar silos on reducing musculoskeletal disorders. Regardless, safety and health experts believe that masons will be less likely to develop musculoskeletal disorders if they use silo mortar dispensing systems on the jobsite.
	Effects on Productivity:	Job productivity is increased because laborers have fewer tasks to perform in order to produce mortar for the masons. Many contractors believe these automated processes reduce material handling by mason tenders, freeing them to do other work, which can also free up jobsite space. Quality of Evidence Manufacturers or vendors have reported an increase in productivity. Safety and health experts believe there is an increase in productivity. Manufacturers of silo systems claim masons are more productive and efficient at the jobsite with these systems. There is no need for cement bag handling and loading, or shoveling sand. The mixing time is reduced allowing the mason more time to work on different tasks. Many contractors believe these automated processes reduce material handling by mason tenders, free-up jobsite space, prevent sand from freezing in winter, eliminate cement bag waste, and allow for easy clean-up and transportation. Because silo systems eliminate the problem of frozen sand, additional productivity gains may be achieved in the winter. Safety and health experts believe reducing the risk of developing musculoskeletal disorders may lead to increased productivity because: 1) masons can work for longer periods with fewer breaks and less fatigue, and 2) there may be a reduction in lost time injuries.
	Return on Investment:	No specific calculation ROI information exists for this particular solution, however, there are some general approaches that might be useful for a “Return On Investment” analysis. For a general discussion of these approaches, visit our “Return on Investment Calculation” page.
	Availability:	Silo mortar systems and bulk bags of pre-blended materials are available from: SPEC MIX, Inc. PROMIX Silo System Equipment like that described here may be available from local retailers or leasing companies. Pre-blended materials are also available: QUIKRETE® is manufacturer that is licensed to produce SPEC MIX as well as their own brand of pre-blended materials. In some parts of the country it may be more convenient to obtain materials from QUIKRETE®.
	Additional Considerations:	When using a silo mortar dispensing system, it is important to assess the risk of silica exposure in the mortar mixing station and ensure that appropriate controls are in place. Silo systems do not eliminate the risk of silica dust exposure in the mortar mixing station; however, dust curtains are available. Specific safety procedures must be followed when loading the silo, climbing the silo's ladder, and moving the system. The silo should be placed in a location that will minimize dust exposure to workers, and will facilitate the safe movement of vehicles/equipment needed to load the silo and handle mortar. In addition to their ergonomic advantages, silo systems can also save space on congested jobsites, reduce material theft, and eliminate the problem of bag disposal (all bulk bags delivered to the jobsite are later removed by the supplier and either reused or recycled). Mortar silo systems with built-in mortar mixers are currently available on the European market. These devices are closed systems. The silo is filled with the mortar components specified by the contractor and then sealed prior to delivery to the worksite. Electrical and water supply connections are needed. The mortar silo systems with included mortar mixers are pictured below.
	Sources:	"Dispensing preblended mortar into conventional mixers," Masonry Construction, August 1996. This solution is also described in: Albers, James T., and Cheryl F. Estill. Simple Solutions: Ergonomics for Construction Workers. DHHS(NIOSH) Pub. No. 2007-122. To access other solutions in that document go to http://www.cpwr.com/simple.html. To order copies of the document, please visit, cdcinfo@cdc.gov, referencing document number 2007-122.