Ceiling Construction Question

Discussion in 'Acoustics (Live Room, ISO Booths)' started by mad-pharaoh, Jul 19, 2018.

  1. mad-pharaoh

    mad-pharaoh Active Member

    Jul 19, 2018
    Falls Church, VA
    Hi all,

    I read Rod Gervais' book, second edition. In the book, he discusses securing 2-3 layers of gypsum between the ceiling joists to add mass to the ceiling and then caulking around the gypsum panels to secure and seal. My questions are: should I use Green Glue caulk for the caulking around the panels or just regular caulk, and is there any benefit to using Greenglue compound between the panels as described for wall assemblies, but not here?

    Thanks! Sorry if this question has come up before, I couldn't find it in a search.

  2. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Jul 21, 2009
    Boston, Massachusetts
    Home Page:
    hey there, green glue or not between the mass layers is common question, and ive never seen official word from rod, but here's how i see it. 1. its not printed in the book, so its either inefficient acoustically or not cost effective. 2. ive never seen test data with GG used in strips, between joists, only full sheets on a wall or ceiling. tested assemblies are the only ones to be considered. 3. green glue is roughly 1.5x the cost of s 5/8 firecode sheet, last time i checked a few years back. 4. the joists themselves are the weak link, so i would save the premium priced product for the part of the assembly that doesn't have an inherent weak link.

    i could see a potential case for it if the structure had a severely limited weight bearing capacity, and could support only one sheet. if that were the case id check with rod before i did anything.

    as far as the caulking to form the surrounding seal, use non hardening caulking- silicone or butyl. that rod actually answered for me here years back with regard to a window assembly. acrylic caulking will harden and crack with time, causing the seal to fail.

    best of luck with your build, and dont forget to stagger the seams.

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