I understand your theory but why not just float with the bonding? It seems like your trying to create a type of suction for hard wall when bonding will do and it will go on tight as ****. Your putting a gypsum based backing coat through your machine so I don't get it and bonding is now similar to hardwall and not as sticky to use but can flash set.I have done it and seems solid but time will tell when it drys and shrinks it might blow. Do you understand my theory @PFTwales
Time to step up a gear now pricey. Nuff of the pictures and put a propper video on showing your lovely clean mixing area. Beautiful spraying action and tranquil working conditions whilst putting hardwall on