Thanks folks. I'll go with it, although I think it's a little tenuous. It's my last clue and has no bearing on the rest of the crossword. Will be sure to check the solution tomorrow though!
James, my dad always used to "size" the walls before hanging wallpaper. He just made up a very thin wallpaper paste, painted it on the walls and waited til it dried before papering.
size2 noun a weak kind of glue used to stiffen paper and fabric, and to prepare walls for plastering and wallpapering. verb (sized, sizing) to cover or treat with size.