...in your new pad of UArt. Glue it to 4ply rag mat.
I ordered this 9x12 pad of UArt 400 grit paper from my usual online art supplier. Must have had a new person in the packaging department because it was bound with stretch wrap so tightly it arrived with a concave bow. I thought I could correct it by stretch wrapping it again in the opposite direction but now it is really confused and has a wave. I will glue it to 4ply rag mat with Sure Mount archival adhesive.