context: took a bit of searching to discover that POP is probably PoP - plaster of Paris and yes plaster of Paris will slow way down if it is not exposed to air - in fact , if you are building up plaster ( `` the way you would icing `` ) to do sculpting , which is rather uncommon , you keep the set plaster damp in order to add more unset plaster or you have to wet the area where you will be adding plaster `` mud ``
hypothesis: The adding happened