The Whirlygig riser/collar system installs in less than 10 minutes and greatly facilitates quality control. After placing the thermoplastic form on the manhole cone, a single crew member cuts the form to grade with the 30-lb radial arm trimmer. Place steel manhole ring and cover on top of the trimmed form and pour redi-mix. The concrete fills the entire cavity, forming a watertight seal and holding the form in place to protect the riser/collar.
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