Fastening drywall between ceiling joists (?)

You know the idea. Adding mass to one layer of ceiling by putting drywall between the joists. I looked at the plans in Rod's book and this is step one for me. One problem I can never find the answer for: How do you fasten it? In the book he cryptically details using finishing nails temporarily, which based on the diagrams appear to be fastened into the joists (as opposed to the subfloor) in a diagonal way, through the edge of the drywall. How does one put a second layer of drywall flush against the first if there are tiny nail heads sticking out? If they are temporary, how do you pull them out while fastening a second layer of drywall? Is something lost/transmission increased by screwing the drywall straight up into the sub floor?

Install both pieces at once?

I like that idea in some respects. My only problem is I was going to green glue the two layers together. This would require me to measure and cut two layers, green glue them (maybe with paint cans on top to smoosh them together more), but then I would only be able to put backer rod and caulk in the lower layer leaving a tiny air space in the one above. Anyone else whose done this project care to weigh in?

Funny, I've been asking myself the same question once. (I never had to fasten mass to the ceiling... YET!) When adding nails, it also seems a frustrating job to add backer-rod.

Totally, are you supposed to pull a nail out, get that section of backer rod in, put the nail back in? Is there any possible way that after putting the backer rod in, and putting the caulk on that the drywall would be able to hold itself up while you put in another layer and secure it with the ledger board? (I strongly doubt it). I'm sure there are some practical methods for this assembly, we just need someone whose done it to speak up. :D

I haven't done it but I believe the idea is to temporarily hold each layer with finish nails. Backer rod and caulk each layer with the nails in place by cutting the backer rod to slip behind the nails. When you add the second layer of drywall the nails get pushed into the previous layer. The same is true when you add your 1x3 cleats to permanently hold everything. Obviously you want to use the smallest/skinniest finish nails feasible. Also, if you have nails protruding through the sub floor, there was a thread a while ago where Rod suggested using 1" or 1.5" foam board insulation as the first layer and just let the nails stick into the foam instead of trying to trim them flush with the underside of the sub floor.

Ok. Well the foam for protruding nails thread lead me to buy foam and put it up under the section of the floor with nails. And I have imagined your described scenario of just leaving the nails in and pushing the next layer of drywall up against them. I guess my only hesitation with that explanation (which seems the simplest so probably the right one) is the effect of leaving the finishing nail's heads to rest between the two pieces of drywall. I could imagine it doing two bad things- a. creating an unwanted airspace between the two pieces of drywall (especially since I'm considering putting green glue in between) b. potentially damaging the drywall which we were already trying to avoid with the pieces of foam against the protruding nails under the floor. But maybe the nails are so small it all comes out in the wash..... Thanks for the input, any others?

Yes....I too wonder.

I thought air space would be a good thing? It's the spring between the mass, isn't it. If the green glue company say you can use a 1/3 of what recommened with good result, I wouldn't be worrying about air. I haven't used backer rod yet, the caulk is fine if you cut your plasterboard accurately.

lilith_envy wrote:

I thought air space would be a good thing? It's the spring between the mass, isn't it.

Remember the mantra Lilith "MSM". Air means a seperation of layers creating multiple leafs

Sorry to bump---- :horse: I guess, I'm just sure someone on here has done this and has a quick answer for myself, and other inquirers. Perhaps my bad (?) for not putting other project details (room is 30'x13.5' with 8' ceilings) but I'm really looking for a fine detail on this particular method, not a response to my over-all build.

Determine the thickness of both pieces of drywall combined or determine the thickness of whatever material you will be using for this mass loading. Once you know this measurement, then measure down from the overhead subfloor and make a mark at this known distance. You will need to have this measurement available down the entire length of the joist as you will need it for this process. I would not use a chalk line. This would not maintain the distance from the subfloor down to your current mark(in the very real event of crowned joists). Install one side of your ledger to the entire length of the joist in question. After the ledger is installed, you can place your piece(s) into the lip created by the ledger. It may take three hands to do this, so be prepared. Have a short piece of ledger material available while you are doing this and you can screw it as a temp piece underneath the mass(opposite the ledger you have it resting on) you just installed until you are ready to install the full ledger piece.

I really like that idea for a number of reasons. It strikes me as the way I should ultimately do this. A couple questions remain: If I want to have green glue between the drywall pieces, should I just green glue them together in advance and put the double piece all together? (I would probably use bricks or weights to compress the boards together achieving the same effect as screwing them together when the green glue is wet). Does having one layer of backer rod on the bottom half of two layers of drywall compromise anything that would be gained by having two separate layers of drywall that are individually caulked and backer-rod-stuffed? Does the build really require ledger board going the entire length of the joist? I always pictured it being foot long pieces put in every couple yards (this is not based on any science, only intuition).