I want to build some John Allen viaducts and can't figure out how he made the liner underneath the viaduct. Some are stone and some are brick. They look very real in the pictures. I have mastered the art of carving tunnel portals and viaducts in plaster of paris but---for the life of me---cannot imagine how to go about carving the liner underneath. Maybe it's too early in the morning. I don't know. I guess a fellow could pour the needed curved liner using plaster of paris like the portals and viaducts and then turn them upside down and carve the bricks and stone. Anyway, I thought there might be some other ideas floating around out there somewhere----hopefully. Did I read somewhere that he used linoleum?