Originally Posted by BIGmouthinDC
The push like hell is to prevent the threads in the upper layer from stripping out and losing grip.
After 30 days two layers of drywall with green glue will not come apart, ever. The best you can do is strip the paper off one layer.
I've done this for walls plenty of times but never on the ceiling where gravity is constantly tugging at the connection from the panel's own weight. It is difficult to balance the right amount of force needed with the drill vs. not stripping out the hole.
I have an old 1/2" OSB / GG / 5/8" drywall access panel cutout and I agree that although not promoted as an adhesive, that Green Glue absolutely has adhesive qualities, not to mention the pockets of suction it creates, much like trying to pull off a tile in wet mortar. The tricky bit is getting to that 30 day mark with no pull-off. Glad to hear you have had good success.
Originally Posted by mijotter
Thanks for the replies. What length screw do you recommend? I have some 2" Coarse thread drywall screws and 1 5/8" or should the screw not "pop" through the first layer?
Provided the screw penetrates both layer, that is really all you would need ..... 1 1/4" minimum. But there is no harm in using 1 5/8" screws where the tip pops into free space beyond the second layer. But where you are going through both layers and into the furring channel you'll want 1/2" to 3/4" penetration through both drywall layers into the aluminum track with the fine thread gripper screws used with metal studs - so 2" screws would be fine.
Originally Posted by tlogan6797
Wouldn't you want the second layer perpendicualr to the first? There should be plenty of screws into channel and the then the seams that don't fall on a channel would need to be screwed into first layer drywall only. Do ANY of the seams need to fall on channel? Wouldn't the scecond layer stop the first layer seams from sagging? It seem (seams?) to me that as long there are sufficient screws in the rest of the of field of the drywall it should stay put.
As long as you have a minimum 4" offset from seams in both directions, you are fine to run the sheet material in the same direction. Most will place the second layer over the first layer's long running seam at the midpoint so there is 24" of seam coverage in both directions and then advance the first sheet one or two studs (channels) to create the offset for the butt seams in the other direction.