During my 40 years in the trades, I've had a number of high-end drywall jobs that required dead-flat ceilings -- no telltale bulges allowed where the ends of the drywall sheets abut one another. The method shown in the drawing is our solution to the problem I've inspected some jobs that we did 25 years ago using this method, and you still can't see where the butt joints occur.
This drywall trick starts with a sheet of plywood. The plywood should be the same thickness as the drywall. First, trim an inch off the width of the sheet, then crosscut it into 10 equal strips. They will be 9-1/4 in. wide by 47 in. long. As shown in the drawing, we next staple strips of 1/16-in. thick poster board to the long edges of the plywood strip.
Before raising a drywall panel for installation, we screw one of the plywood strips to the end of the panel. The poster-board strip goes between the plywood and the drywall. As the drywall goes up, the butt ends are arranged to fall between the ceiling joists. When the adjacent drywall panel is screwed to the plywood strip, a shallow dip is created where the drywall bends over the poster board. This shallow dip creates a hollow for the tape.
We tape our joints in the usual manner, beginning with the butt joints. Once that joint compound has dried, we tape the long edges. Incidentally, a 20-in. long piece of 1-1/2-in. aluminum angle is a handy tool for leveling the finish coats of joint compound over the butt ends. Using this technique, we never had a joint show up on a punch list at the completion of a job.
Tim Hanson, Indianapolis, IN