THE PROCESS

Determine Strength & Thickness Ratio Many factors impact optimum design thickness, i.e., the condition of the existing manhole, its material composition, depth, degree ovality, groundwater pressure, and traffic loads. The design engineer should determine the most appropriate combined value in each case. Use the manufacturer's design guide for detail. At the strength levels of the specified mortar, a thickness of 1/2" is appropriate for most manholes up to depth of 12 feet. Mortars that develop less strength to thickness ratio may be used with customer approval when applied at 1.5 times the prescribed thickness. Washing Preparation Cover the manhole base to prevent washed debris from entering the sewer line. Wash the interior surface with a high-pressure water blast, usually 3,500 psi, sufficient to remove all laitance and loose material and flush debris downward to the covered base. Pressure sufficient to etch the existing surface will improve adhesion. Plug any active leaks with plugging material as necessary. Equipment & Mixing Mortar mixers, compressors and pumps are standard commercial models. The high-speed, rotating applicator device is used to provide a densely compacted liner of uniform thickness and thorough coverage. Combine mixture according to manufacturer's directions with a high-speed shear mixer. Agitate mortar to prevent thickening beyond desired fluidity, approximately 40 minutes. Mix in MIC protection at prescribed amounts. Application Spin-Cast Washer No-Entry Application Radial Compaction Position the rotating casting applicator within the center of the manhole at the lowest point desired for the new wall and commence pumping the mixed mortar. As the mortar begins to be centrifugally cast evenly around the interior, retrieve the applicator head at the prescribed speed for applying the thickness that has been selected. Controlled multiple passes are made until the finished thickness is attained. Determine appropriate thickness of cementitious liner in accordance with manufacturer's recommendations. For additional thickness, place rotating applicator at location and pump and retrieve until area is thickened. Finishing Pressure application from the centrifugal casting of the mortar produces an orange peel surface that requires no additional troweling or finishing. Brushing is an optional procedure texturing it's finish for improved mechanical adhesion with coating. Clean up The base covering is removed and any debris disposed of properly. Additional material is hand applied to bench surfaces at a thickness of 3" tapering from the wall to the edge of the channel. Flows at bottom channels may remain active during the procedure.

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Date of last update: December 1, 2000

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