The darker gray areas are the seams where one sheet of drywall abuts another. The drywall has tapered edges, so the plaster is thicker in these areas. It’ll take approximately one week to dry, at which time it is safe to paint. This will be our next step.
One other thing - plaster makes a unbelievable fucking mess. They’re basically taking a wet, mud like substance a sloshing it onto the walls. About half of it gets there. The other half gets on the floor, behind closed doors (somehow), all over the windows, in electrical outlets, everywhere. It doesn’t matter if the floor is covered with tar paper and the shelf with plastic, it’s there. It’ll take you twice as long to clean as it took the guy to do the work.