Sealing drywall 1st layer

Hey guys, for retaining the isolation characteristics of the drywall itself, after installing the first layer of drywall, what is the best way to seal up the gaps? Is regular drywall mud ok or is using a construction adhesive or latex caulk a better idea? Because I have some larger gaps in the corners especially that would require a lot of stuff, and drywall mud is much less expensive. Also, is it beneficial to use an adhesive or caulk on the drywall face, in between the 1st and 2nd layers? - in the way green glue is used.

For the edges, the general recommendation is to use backer rod pushed to the back of the gap, then caulk over that with flexible caulk that never hardens, or even better, proper acoustic caulk.

Also, is it beneficial to use an adhesive or caulk on the drywall face, in between the 1st and 2nd layers? - in the way green glue is used.

Definitely not! You should never glue the layers of drywall together, as that totally changes the characteristics of the panel. Green Glue is not actually glue at all (despite the name): it is a visco-elastic polymer that acts as constrained layer damping between the layers. It never hardens, and is designed specifically for that job, not to glue panels together. You cannot substitute anything else: it simply won't work. So just put up the second layer directly on top of the first layer (staggering the joints so that they don't line up with the first layer) and attach with screws in the normal manner, into the studs, using screws that are 5/8" longer than ordinary drywall screws. - Stuart -

Thanks Stuart! As far as the flexible caulk, I assume most latex based caulks, or a kitchen/bath type of caulk would fit the bill right?

As long as the caulk never hardens, and remains flexible and rubbery, even after years, it should be OK. Of course, it should also never shrink or come unstuck from the layers it is sealing, due to vibration, expansion, contraction, etc. So get a good quality type, with a proven track record. But yes, the types commonly sold for sealing bathrooms and kitchens are a good option. - Stuart -

Thanks Professor. ;)