Drywall Questions

Hi all, I have two simple drywall questions:

1. I'm preparing to install isolation clips and hat channel on my ceiling. The manufacturer's instructions describe placement of clips and hat channel but nothing of the drywall itself. I've installed lots of drywall before - the edges are always screwed (or nailed) to a stud or joist. As such, neighboring sheets are held together by sharing a common stud or joist. Is this the same approach to be used with hat channel? This seems a little awkward when each hat channel is 24" apart and no closer than 6" to some walls. Consequently, those sheets must all be trimmed down to 24" + 6". Otherwise, the inside joints will be suspended in mid air (as indicated in the attached drawing), and I suspect any compound used to join the seams will eventually fall apart. [After all, the ceiling is supposed to move, right?]
2. On studio walls, should I apply standard drywall joint compound and mesh tape between adjacent drywall sheets? Or, is there some special technique or material to use instead? I have plenty of sound insulation caulk but can't imagine it being necessary here. BTW, these walls will not show, so they needn't be finished all the way (and won't be painted) - I'm only applying joint compound for the purposes of sound isolation.

Any advice is greatly appreciated!

Here's a prettier diagram of my ceiling problem. After some Tetris-inspired manipulation, I came up with a drywall cutting and placement diagram that meets all of these presumed requirements:

1. Drywall pieces are cut so that edges occur on hat channel boundaries, for stability (as is typical with traditional drywall installation on joists)
2. Perimeter pieces are cut and positioned to span at least one full 48" gap (two hat channels) for sufficient support
3. Layers (blue and red) do not share any edges for optimal rigidity and sound isolation

For clarity, I've again shaded a few of the drywall pieces and you can see the problem: it's a real mess of a patchwork quilt, and lots of drywall is wasted to make it all work. Have I got this right or is there a better way? Thanks again. ps. Is anything easy with studio construction?! :shock:

Or, there's this. Turning all the boards horizontally, I can just meet the above requirements (assuming they're indeed requirements) without the kludgy patchwork after all. Sweet n' simple - ten sheets of drywall per layer. In this drawing, full sheets of drywall are shown, for simplicity. So, the question remains: is this ideal, or am I missing something? Aside from Green Glue between the layers, is there anything special about joining the seams (e.g., traditional joint compound and tape?) [To be clear, the perimeter of the ceiling will feature a 1/4" gap from the walls, to be filled with acoustic caulk.] Thanks again. Sorry for blathering on and on, but even without any responses yet, it helps to talk through it. [You're such good listeners. :mrgreen: ]

hey there Dave, I'm no drywalling expert but.....with my build I hung the first layer of ceiling plaster with the long seams of the plasterboard running perpendicular to the hat channel (paralell with the ceiling joists) and taped and mudded them. My second layer was hung the same way (perpendicular to the hat channel) but I offset the long seams so they were in the center of the first layer of plasterboard. I then taped and mudded those seams. Obviously the second layer of plasterboard was screwed through the first layer to the hat channel making it incredibly ridgid. I also used green glue between layers. I don't believe the movement in the isolation mounts is so severe that it will break a scrwed, taped and mudded joint in the second layer. My other reason for not having any concern is that 16mm plasterboard screwed to hat channel at 450mm centres is very ridgid surface. hope that makes sense :D

Your 3 rules make sense, Dave, and yes Steve is absolutely right: you do need to mud and tape the joints on both layers, and you do need to offset the joints between layers. Some people do "backer rod and caulk" instead of mud and tape, and you have to do that at the edges anyway (where the ceiling meets the wall). I would try to ensure that you get as many edges as possible over hat channel. One other pointer: Be VERY careful with your screws! You cannot have even one stray screw that accidentally touches a joist. Not even one. So mark your joist positions with great care as the drywall goes up, and leave a good margin around those when you do your screwing schedule. As a second precaution, use only screws that are the right length to go through the hat channel and out the other side properly, but not long enough to hit the joists, and use screws that are 5/8" longer for the second layer, for the same reason. It is critical that your screws do not touch the joists, only the hat channel. - Stuart -

I got it right? That's a first for this project. Must be a rift in the space/time continuum somewhere. Good advice re mudding & screws too. Will do. Thanks guys!

Must be a rift in the space/time continuum somewhere.

Dr. Who reference? :) So maybe your studio will end up "bigger on the inside"... :!: :wink: - Stuart -

Hahahaha!!! If only it were true.