Gotcha.Quote:
when beefing up my outer leaf for mass, would it be ideal to green glue each layer of drywall (if that's the material I choose to use), or does it make little difference?
You can look up the technical documents on Green Glue's website. You'll learn that the stuff is pretty magical. It offers great results without eating up space. It's really easy to install, much easier than adding more layers of heavy material. Basically, it's highly recommended.
...when applying Green Glue, would it be ideal to trowel it onto the walls, or is that unnecessary?...I've seen it applied in a random zigzag motion, on pieces of drywall that were laid face down, but I'd rather hear how you'd do it, in the real world.
Well, wood and drywall are out the window, I'M GOING 4" OF STRAIGHT LEAD!!!Quote:
I have access to a bunch of free ply/osb sheets, and was curious if wood offers the same quality of "beef" that drywall does, in this application, between studs on the interior of the building? That would be nice if it did.
Awesome. Use them. Wood does offer the same "beef" that drywall does, just differently. By differently, I mean that different materials have different surface densities. The reason drywall is often used is because it has the best cost to mass ratio. The only downside to you using something like plywood over drywall is that in order to obtain the same mass, you will have to use thicker/more layers of plywood. Thicker beef up material = smaller gap between your masses of your MSM system (unless you move your inner leaf further from your outer leaf which would also result in a smaller room). Heck, if we all could afford it, I'm sure we'd use materials like lead for our walls.

All sarcasm aside, I'm into the idea of saving every inch that I can, and I would also prefer to work with drywall over sheets of ply, so I'll likely just go the 5/8" gypsum route.
Your cost to mass statement was very insightful, way to nail that down for me, Greg.

Would you recommend that I apply 5/8" drywall between the ceiling joists also (control room floor), to acheive more mass there also? Any other advice about that situation?
Ok, great, that is encouraging to hear...I found a couple threads that mention the cleats, but have yet to actually see a picture of them in use, for reference. Do you have an image available, or can you point me in the right direction, so I can better visualize my approach?Quote:
I have gathered that cleats and side nailing are the idea here?...I'd love to understand that method clearly, if you wouldn't mind elaborating a bit.
I think you're completely understanding the procedure. Put up your beef up material (with GG between if you choose to do so) and press it up as tightly as you can. Install the cleats to hold the material in place. Obviously, seal around each layer with GG Sealant. That's it. It's a pain in the ass job, but obviously worth it.
...know of any hospitals closing down around Chicago? Haha..Quote:
The reason drywall is often used is because it has the best cost to mass ratio. The only downside to you using something like plywood over drywall is that in order to obtain the same mass, you will have to use thicker/more layers of plywood.
Right! The density of drywall is around 680 kg/m3, while the density of plywood is only around 560 kg/m3. So you would need plywood that is 22% thicker to get the same mass. MDF is actually better than drywall: around 750 kg/m3. But it's also quite a bit more expensive. OSB is similar to plywood but a bit better: around 600 kg/m3. So you need OSB that is around 15% thicker to get the same mass as drywall.
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Heck, if we all could afford it, I'm sure we'd use materials like lead for our walls.
For sure! Lead sheeting is around 12,500 kg/m3! Yep, you read that right: About EIGHTEEN TIMES the density of drywall. So instead of two layers of 5/8" drywall, you could have a sheet of lead foil just 1/16" thick, and still have the same total mass. Lead is also "limp mass", which makes it even better for isolation.... on the other hand, it ain0t cheap, and is difficult to work with. However, there are some rather specialized products out there, that consist of thin lead sheeting embedded in drywall. Used for shielding places where radiation is a problem, such as hospital X-ray rooms, MRI and NRM rooms, science labs where radiation is an issue, etc. You can buy that stuff for your studio if you want: Huge amount of mass in a thin panel. But huge price tags, too!
The above numbers really give a lot of perspective, I wouldn't have guessed that plywood was so inferior to drywall, regarding mass. Interesting.
Again, 5/8" will likely be my choice,...I'm glad to be armed with all this newfound knowledge!The normal recommendation is plain old 5/8" (16mm) fire-rated drywall, because as Greg mentioned, its the best compromise on price: reasonably high mass, lowest price per kg (or pound) of mass. It's also easy to work with. But there are alternatives, if you have lots of money and a need to save space. Even steel plate is good, at around 7,800 kg/m2 (11 times density of drywall. So is aluminium plate: 2,800 kg/m3 (4 times density of drywall). It's all about cost/benefit.
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Obviously, seal around each layer with GG Sealant.
Sealing is critically important, yes, but I'm not to keen on GG sealant. The actual GG compound is the best stuff out there, bar none, but their sealant isn't so good: it tends to shrink a bit as it dries, so it can crack if you apply it thick. And if you apply if thin, you need two or more layers... There are better sealants out there. So, to be clear: Green Glue compound between layers of sheeting: YES! Absolutely. Green Glue sealant: Not so much. Use alternatives.
Is steel plate used in this application commonly?...I never even thought of that. Probably good to block RF interference too, wouldn't you think?...not that I have that problem, just curious.
...and the actual, brand name GreenGlue compound is the best, you say, Stuart?...any recommendations for a source of said compound, besides online, or is that my best bet?...I'll be sure to look up the other's that were posted too, I'm sure there's a dealer with one of your recommendations around here somewhere, as I'd rather buy buckets locally, when I need them, though whatever dealer offers the best product at the cheapest cost would surely be preferable.
Thanks again fellas, I hope that you're getting paid psychologist rates, because you've already talked me off the ledge!
