FireLake P77-3-SC30 Installation And Operator's Manual page 11

ALL FLANGE CONNECTIONS
Purpose: create air tight flange to flange connection and
continue a refractory lining from stack to stack. IF mastic is
used and pushes out seam smooth to match interior wall.
Mastic is also called "furnace cement" "mud".
P77-3 SC30 Manual 9.27.2019 Page 11