rubberized pick up truck bed liner spray.........................................................................no kidding
I've mentioned before when this topic comes up, that way back when, we used a product called Pro Seal, a catalyzed rubber that was initially developed as an aviation fuel tank sealer/liner. It both sealed the mesh/frame joint, and masked like tape.
We used various films for stencils, but its rubber grip and ensuing friction would probably not have been conducive for direct emulsion application. It's flexibility was great though.
Seems to have left the market in the early eighties, and when I returned to a screen printing, and a screen department in a shirty shop in the late eighties, at my suggestion, we experimented with the Liquid Tape and other frame glues, but no one liked them. Besides, they had a hundred times more screens than we had in the flat stock shop I had worked.
