1. Getting too much pleasure from ripping a plaster (as in Band-Aid) off a wound and thus getting aroused, leading to the above word.
2. What occurs when a decorator gets bored/horny doing his job, then adding his "produce" to the mix of plaster that's going on the wall.
1. Ripping off the hair around my cut was such a good pain that I had to indulge in plasterbation.
2. After plastering half the room in Mrs. Smith's house, I got bored so I whacked off into the plaster tray in a fit of plasterbation. The walls might be a bit smelly in places.