A Grade Ring has grooves on the underside and a tongue on the upper side to form a tongue and groove joint between multiple Grade Rings and Finish Rings. A manhole frame should never be installed on a Grade Ring. Finish Rings have grooves on the underside and are mostly flat on top with a groove located on the inside diameter which is there to accept and lock in an Angle Ring if used.
PRO-RING’smay be vacuum tested and the test should not be performed until after the adhesive has been cured for a minimum of 24 hours. Any vacuum testing that is conducted should be done in accordance with ASTM C-1244, “Standard Test Method for Concrete Sewer Manholes by the Negative Air Pressure (Vacuum) Test Prior to Backfill.
There are other materials that may work, however all of our testing related to vacuum testing and exfiltration testing has been performed using the M-1 Adhesive. Please contact us or your local representative regarding possible substitutions.