A system and method are disclosed for sealing an annular manhole riser ring assembly. A generally flat, bendable liner includes a flat strip that is generally conformably engageable with an interior circumferential surface of the riser ring assembly. An outer surface of the liner strip carries a plurality of spacer elements that form a void between the generally flat liner strip and the engaged inner circumferential surface of the riser ring assembly. An expandable tensioning device is operated to press the riser ring assembly against the circumferential surface of the riser ring assembly. A flexible bonding substance is introduced into the void and allowed to set to seal the riser ring assembly.