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post #61 of 519 Old 01-23-2014, 06:07 PM - Thread Starter
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Originally Posted by 30peppered View Post

Question: This soundproofing neophyte could use some sage advice from the Grand Masters. Here's the skinny: we bought a home with a mostly finished basement apartment with 7 foot ceilings in said apt. Due to some incredibly poor workmanship in framing, we needed to open up half of the basement ceiling to reinforce floor joists.

1) To improve soundproofing, I am planning on adding R13 to the 2x8 floor joists then hanging 5/8 Quiet Rock. With no room for hat channel, does this make sense?

The Soundproofing Company has a pretty good page on this topic and show several solutions:

Soundproof a Ceiling

None of them will directly fit your situation, but if you combine some ideas, you can come up with a good approximation of some solutions. Some thoughts:

1. You might consider adding another layer of 5/8" drywall to the floor, between the joists, sandwiching Green Glue between the floor and drywall. This will give you some mass and damping, but without intruding on the ceiling height below
2. If you can spare another 5/8", then it would be a LOT cheaper to go with two layers of 5/8" Type X drywall with Green Glue, than a layer of Quick Rock. The performance would be very similar.
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post #62 of 519 Old 01-24-2014, 07:16 AM
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Thank you for asking this question, because I'm going to have to do the exact same thing in my theater. In my case, it's not a basement, but it is still two very large windows that cannot be permanently covered.

The best build thread on a window plug that I've seen so far is in the Dark Knight Theater thread. Here's a link to the post with some details: The Dark Knight Theater - Window Plug Details Post

I'm still searching for even more details on pros/cons and possibly other options, if they exist.
Check out my window plug http://www.avsforum.com/t/1468993/the-retirement-dream-home-theater/210#post_23740019
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post #63 of 519 Old 01-24-2014, 07:29 AM
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Originally Posted by granroth View Post

Okay, so here's my thoughts on how you might construct a pretty massive wood-frame concrete-filled door. This is assuming a 32" x 80" door.

First, start with a layer of 1/4" ply then Green Glue then a layer of 3/4" MDF. On the bottom of this is an automatic door seal (I spec'ed a Zero International partial mortise).

Massive Door - Layer 1

Then, create a wood frame using 2x4s and 2x4s ripped in half (1-1/2" x 1-5/8", accounting for the width of the saw blade). This creates 8 cavities. Line the cavities with poly film and fill them with concrete. Let the concrete cure for at least a week.

Massive Door - Layer 2

Add another layer of poly and then a layer of 1/4" ply capped with a slightly smaller layer of 3/4" MDF.

Massive Door - Layer 3

Before getting to the specs, I wanted to cover a couple points. The slightly smaller layer of MDF is intended to create a "bank vault" effect, with staggered door seals. This double seal should do a fantastic job of blocking any air leakage. The Green Glue is important because mass without damping only covers half the battle. A quote from Ted White from another thread:
The 1/4" ply is there simply because this door is already quite thick. As I write that, I realize that it would make more sense to use two layers of 1/2" MDF than 1/4" Ply + 3/4" MDF. It would be more dense and damping works best with layers that have the same mass and density, anyway.

So what are we looking at?

This door is 3-1/2" thick (roughly twice the width of a standard door) and is massive. How massive?

Assume that MDF is 49 lbs cu ft; Plywood is 32 lbs cu ft; concrete is 133 lbs ct ft; and Douglas fir studs are 31 lbs cu ft. There are 0.731 cu ft of plywood, 2.122 cu ft of MDF, 0.662 cu ft of wood, and 1.56 cu ft of concrete. Do the calculations and you have a door that weighs 355 lbs!

(Actually, it would be slightly more than that if you replace the plywood with MDF)

Is that enough?

Well, JH Brandt suggests that the door must have at least as much (and preferably) mass as your walls. If you assume that you have double walls with two layers of 5/8" drywall on each side and further assume that the insulation has negligible mass; the studs add only a little; and drywall is 2.2 lbs sq ft, then we have a mass of 8.8 lbs sq ft for the walls. Round up to 9 lbs, factoring in the studs.

Our door is 32" x 80", which is 17.8 sq ft. If we want our door to have at least as much mass as our walls, then it would need to be 17.8 x 9 = 160 lbs.

Our actual door is more than TWICE that massive. When you consider that it is also damped and fully sealed, then it's hard to imagine that this door wouldn't do a fantastic job of sound proofing.

Maybe too good, actually. Overkill is sometimes good, but exceeding the mass by that much might not be justified. That's a pretty extreme door.

I also have NO idea if it would actually work, since I haven't seen it done.
It took 3 men to carry my window plug up the steps from the garage. Better build that in place! eek.gif Check out stockmonkey200's door
http://www.avsforum.com/t/1314492/desert-sunset-theater-build/210#post_20588441
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post #64 of 519 Old 01-24-2014, 07:49 AM
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Originally Posted by joshp14 View Post

If using first layer OSB and second layer drywall, does one still need to worry about hitting the studs and channel with screws when hanging that second layer?

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Originally Posted by granroth View Post

I'd be about 90% certain that the answer is that you can screw the second layer of drywall in anywhere, since you are using OSB. Curiously, though, I haven't tracked down anybody saying that explicitly. There's a lot of suggestions to that effect, though.

See some of the later posts in this thread: Does OSB seem all that less dense?. The strong implication is that they are installing the drywall without having to worry about screw placement.

But yeah, I'd like to get direct confirmation of that as well. The only non-ambiguous examples I've heard all center around attaching internal components and structures, not the drywall itself.
I was told by Ted White to hit the hat channel for the second layer. the weight of both sheets of materiel will be too much for the channel given the amount of screws you put in the first layer. You buy drywall screws for the metal channel in 2 lengths 1 1/2" for OSB layer and 2" for DW layer. Just use chalk and snap a line where your channel is on the OSB as you go and same for the Drywall. Comes in handy later when doing soffits and columns to also hit the channel. The more weight you have in the channel the better!
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post #65 of 519 Old 01-24-2014, 03:32 PM - Thread Starter
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Originally Posted by cw5billwade View Post

Check out my window plug http://www.avsforum.com/t/1468993/the-retirement-dream-home-theater/210#post_23740019

Yep, your window plug is in the 'Notable Soundproofing Threads and Links' post (second post of this thread). I love it because it's such an extreme example!
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post #66 of 519 Old 01-24-2014, 03:41 PM - Thread Starter
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Originally Posted by cw5billwade View Post

It took 3 men to carry my window plug up the steps from the garage. Better build that in place! eek.gif Check out stockmonkey200's door
http://www.avsforum.com/t/1314492/desert-sunset-theater-build/210#post_20588441

Thanks, I updated the the Notable Links. That series of posts goes into a great level of practical detail.
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post #67 of 519 Old 01-24-2014, 03:46 PM - Thread Starter
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I was told by Ted White to hit the hat channel for the second layer. the weight of both sheets of materiel will be too much for the channel given the amount of screws you put in the first layer. You buy drywall screws for the metal channel in 2 lengths 1 1/2" for OSB layer and 2" for DW layer. Just use chalk and snap a line where your channel is on the OSB as you go and same for the Drywall.

Interesting! I guess the thinking is that X number of 1-1/2" drywalls screws can only hold Y lbs of weight and the combined total of OSB+DW exceeds that?
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Comes in handy later when doing soffits and columns to also hit the channel. The more weight you have in the channel the better!

Mentioning soffits and columns, though, does directly conflict with my understanding of using OSB in the first place. The major reason stated for using OSB has always been that you can attach things like soffits and columns wherever you want and not have to worry about hitting the channels. If hitting the channels is still worthwhile, then there are almost no benefits to using OSB as the first layer!
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post #68 of 519 Old 01-24-2014, 08:55 PM
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Thank you, I appreciate the feedback. I'm going with GG and 5/8 rock between joists after looking at the soundproofing link. You guys are great, thanks for the help~
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post #69 of 519 Old 01-24-2014, 09:50 PM
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I was told by Ted White to hit the hat channel for the second layer. the weight of both sheets of materiel will be too much for the channel given the amount of screws you put in the first layer. You buy drywall screws for the metal channel in 2 lengths 1 1/2" for OSB layer and 2" for DW layer. Just use chalk and snap a line where your channel is on the OSB as you go and same for the Drywall. Comes in handy later when doing soffits and columns to also hit the channel. The more weight you have in the channel the better!

Re the chalk line -- put marks on the perpendicular surfaces indicating where the channel is before you put the drywall up. (if it's a wall then the perpendicular surfaces the right angle walls; if it's a ceiling then the perpendicular surfaces would be the walls). This makes it easy/obvious/quick/idiot-proof to do a chalk line.

Re putting screws into the channel. Reminds me of the 1981 Hyatt Regency walkway collapse. The nuts were designed to hold a certain amount of weight, namely the entire walkway full of people jumping up and down to the music. But instead of running a single strong rod all the way down (original design), they used half length rods (actual construction). This meant that the upper deck nuts were holding double the weight, which they were not engineered to take, resulting in 111 immediate deaths, 3 more deaths a few days later, and 219 injuries.
HRWalkway.svg
from http://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse

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post #70 of 519 Old 01-24-2014, 10:00 PM
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Originally Posted by granroth View Post

Interesting! I guess the thinking is that X number of 1-1/2" drywalls screws can only hold Y lbs of weight and the combined total of OSB+DW exceeds that?

I would imagine that it's a question of compressibility.

Steel is great under tension. Concrete is good under compression.
Imagine a twist tie. Tie a 1 pound weight to one end, and pull on the other end, and the 1 pound weight lifts. Now hold that twist tie vertically, and balance a 1 pound weight on the top -- the twist tie bends and the weight falls. Steel is great under tension, but lousy under compression.
Imagine a hollow cinder block (the kind with two holes, that round these parts they make public schools out of). Park a car on top of it, no problem. Tie a rope through one end of the cinder block, and another rope thorough the other hole down to the car, making the cinder block a chain link, and use a crane to lift the upper rope, and the cinder block snaps in two and the car falls. Concrete is great at compression, but lousy under tension.
(this compression tension bit is how rebar works in concrete floors and bridges, and why you put rebar at the bottom of the concrete floor because that's the part that stretches -- and stretching is tension, whereas the top of the floor is under compression when there is load)

Think of the shape of a screw. Its not the thread that holds the drywall in place, but the head of the screw compressing the gypsum.

Think of a screw driven into drywall. Now pull on that screw with 100 pounds of force, and the screw rips right out. That's because gypsum is lousy under tension.

Drive that same screw into steel, and the steel screw itself is great under tension, the screw head is acting on the drywall keeping the drywall under compression. How many screws have you seen made out of concrete, that are under tension load.

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post #71 of 519 Old 01-25-2014, 10:15 AM
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Originally Posted by BasementBob View Post


Snip.....

Think of a screw driven into drywall. Now pull on that screw with 100 pounds of force, and the screw rips right out. That's because gypsum is lousy under tension.

Drive that same screw into steel, and the steel screw itself is great under tension, the screw head is acting on the drywall keeping the drywall under compression. How many screws have you seen made out of concrete, that are under tension load.

A few thoughts..

In this situation the "weak link" in the Clip/Channel/OSB/DW stack up is the pullout (tension) of the screw in the Very Thin (.018) 25 ga. channel. With an pull out under tension (ceiling) of ~ 130 lbs, (if using 20 ga channel the pullout jumps to ~ 280lbs.) Compared to wood (pine/fur) at approximately 3x this value.

These numbers were average ultimate's and did not include a safety factor, which would drop the operational values to ~ 60lbs of tension for the ceiling. Thus the recommendation for hitting the channels when installing the second layer if screw spacing is done per code.

Under shear (walls) the pull out of the screw from the channel is naturally higher (>500 lbs for 25ga) since the force is vertical and less of a concern than the ceiling. Oddly enough the shear values for 20 ga were lower than the 25 ga, I assume because some bending of the thinner channel happens before failure in this axis.
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Originally Posted by granroth View Post

I'd be about 90% certain that the answer is that you can screw the second layer of drywall in anywhere, since you are using OSB. Curiously, though, I haven't tracked down anybody saying that explicitly. There's a lot of suggestions to that effect, though.

See some of the later posts in this thread: Does OSB seem all that less dense?. The strong implication is that they are installing the drywall without having to worry about screw placement.

But yeah, I'd like to get direct confirmation of that as well. The only non-ambiguous examples I've heard all center around attaching internal components and structures, not the drywall itself.

Now consider the pullout force of a #6 screw in 5/8 OSB is actually higher than it is in the channel at ~ 270 lbs. You are able to attach internal components securely with a osb/dw stack up but the weak link is again the number of screws holding the layers in the channel.. Personally if I wasn't going to hit the channel on the second layer I would double up on the screws in the first layer. Im talking about the overall attachment of the panels here and not necessarily the seams.. I don't believe it is necessary that the seams need to hit the channel on the second layer particularly if you used OSB on the first.

I would think that most people who have screwed OSB into hat channel will tell you that you need to press the panel to the channels to secure it, and you can not rely on the screw to pull it tight.. more times than not the screw will strip in the channel if your not pressing on the panel, over-driving the screw Ie.. trying to set the head into the OSB will also cause the screw to strip in the channel. This is just one indicator of the lower pull out force of the screw/channel compared to conventional framing.

Drive a screw into a piece of hat channel you'll be surprised how easily you can pull it out with a pair of pliers. wink.gif
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post #72 of 519 Old 01-25-2014, 11:57 AM
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Originally Posted by granroth View Post

Interesting! I guess the thinking is that X number of 1-1/2" drywalls screws can only hold Y lbs of weight and the combined total of OSB+DW exceeds that?
Mentioning soffits and columns, though, does directly conflict with my understanding of using OSB in the first place. The major reason stated for using OSB has always been that you can attach things like soffits and columns wherever you want and not have to worry about hitting the channels. If hitting the channels is still worthwhile, then there are almost no benefits to using OSB as the first layer!
that is correct but it is best is to plan your soffits to hit a hat channel. I knew I wanted 12" deep soffits so I added an additional Hat channel in that location. Also since I snapped a chalk line where the hat channel was when the soffit was perpendicular I put the screw on the line. you can tell a difference when the screw hits channel and just OSB it is just not as firm in OSB only. That being said there were manny times on the second layer of drywall a piece did not end on a channel do to over lapping the edges. Then the OSB is really great. same with my coffers most of them did not hit channel. For the columns I just screwed where ever I needed to.
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post #73 of 519 Old 01-25-2014, 11:59 AM
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Originally Posted by granroth View Post

Yep, your window plug is in the 'Notable Soundproofing Threads and Links' post (second post of this thread). I love it because it's such an extreme example!
I updated the thread prior to the window plug to better explain how I did the window frame and sill to keep them decoupled.
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post #74 of 519 Old 01-25-2014, 12:05 PM
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Originally Posted by BasementBob View Post

Re the chalk line -- put marks on the perpendicular surfaces indicating where the channel is before you put the drywall up. (if it's a wall then the perpendicular surfaces the right angle walls; if it's a ceiling then the perpendicular surfaces would be the walls). This makes it easy/obvious/quick/idiot-proof to do a chalk line.
Yes I put the piece 6 inch from corner than snapped a line across it centered on the hat channel then slide piece into place and screwed it in. Next piece snap line etc. Same with dry wall. then you always know where the channel is.
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post #75 of 519 Old 01-25-2014, 12:12 PM
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Originally Posted by BasementBob View Post

I would imagine that it's a question of compressibility.

Steel is great under tension. Concrete is good under compression.
Imagine a twist tie. Tie a 1 pound weight to one end, and pull on the other end, and the 1 pound weight lifts. Now hold that twist tie vertically, and balance a 1 pound weight on the top -- the twist tie bends and the weight falls. Steel is great under tension, but lousy under compression.
Imagine a hollow cinder block (the kind with two holes, that round these parts they make public schools out of). Park a car on top of it, no problem. Tie a rope through one end of the cinder block, and another rope thorough the other hole down to the car, making the cinder block a chain link, and use a crane to lift the upper rope, and the cinder block snaps in two and the car falls. Concrete is great at compression, but lousy under tension.
(this compression tension bit is how rebar works in concrete floors and bridges, and why you put rebar at the bottom of the concrete floor because that's the part that stretches -- and stretching is tension, whereas the top of the floor is under compression when there is load)

Think of the shape of a screw. Its not the thread that holds the drywall in place, but the head of the screw compressing the gypsum.

Think of a screw driven into drywall. Now pull on that screw with 100 pounds of force, and the screw rips right out. That's because gypsum is lousy under tension.

Drive that same screw into steel, and the steel screw itself is great under tension, the screw head is acting on the drywall keeping the drywall under compression. How many screws have you seen made out of concrete, that are under tension load.

More like you put about 21 screws per 4x8 sheet which holds the weight of the OSB no issues. Hat channel is thin. If you screw to tight the channel will lose and screw just spins and pops back out. It took a few until I learned the pressure required and when to stop screwing to prevent it from popping the channel. So given the 21 screws holding the OSB now add the weight of the dry wall without hitting the channel and the channel will lose. Always best to hit the channel when you can. I had some drywall edges where I had to just hit the OSB because it did not hit a channel but that is 5 screws out of the 20 so no biggie.
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post #76 of 519 Old 01-25-2014, 12:15 PM
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Originally Posted by KNKKNK View Post

A few thoughts..

In this situation the "weak link" in the Clip/Channel/OSB/DW stack up is the pullout (tension) of the screw in the Very Thin (.018) 25 ga. channel. With an pull out under tension (ceiling) of ~ 130 lbs, (if using 20 ga channel the pullout jumps to ~ 280lbs.) Compared to wood (pine/fur) at approximately 3x this value.

These numbers were average ultimate's and did not include a safety factor, which would drop the operational values to ~ 60lbs of tension for the ceiling. Thus the recommendation for hitting the channels when installing the second layer if screw spacing is done per code.

Under shear (walls) the pull out of the screw from the channel is naturally higher (>500 lbs for 25ga) since the force is vertical and less of a concern than the ceiling. Oddly enough the shear values for 20 ga were lower than the 25 ga, I assume because some bending of the thinner channel happens before failure in this axis.
Now consider the pullout force of a #6 screw in 5/8 OSB is actually higher than it is in the channel at ~ 270 lbs. You are able to attach internal components securely with a osb/dw stack up but the weak link is again the number of screws holding the layers in the channel.. Personally if I wasn't going to hit the channel on the second layer I would double up on the screws in the first layer. Im talking about the overall attachment of the panels here and not necessarily the seams.. I don't believe it is necessary that the seams need to hit the channel on the second layer particularly if you used OSB on the first.

I would think that most people who have screwed OSB into hat channel will tell you that you need to press the panel to the channels to secure it, and you can not rely on the screw to pull it tight.. more times than not the screw will strip in the channel if your not pressing on the panel, over-driving the screw Ie.. trying to set the head into the OSB will also cause the screw to strip in the channel. This is just one indicator of the lower pull out force of the screw/channel compared to conventional framing.

Drive a screw into a piece of hat channel you'll be surprised how easily you can pull it out with a pair of pliers. wink.gif
+1
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post #77 of 519 Old 02-04-2014, 06:30 PM - Thread Starter
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I want to talk about sealants a bit. We've already established in this thread that sealants are essentially a part of the damping process, but haven't really discussed what kind of sealants are necessary. The most common suggestion is to use a dedicated acoustic caulk like SilenSeal. But does that do a testably better job than "normal "caulk"? Here's a quote from @Ted White from a different thread:
Quote:
Originally Posted by Ted White View Post

Sealant primarily seals for air penetration. Let's establish that.

No lab has ever, nor will likely ever, test such a nuance, so we can mentally spin this for years.

15 years ago, people used fiberglass instead of damping compound in a similar application and sealant was used at the edge of the drywall.

When this technique was adapted using damping compound, the use of sealant at the edge of the drywall was maintained. The thought at the time was that the sealant helped to bond the system together, allowing the floor being treated to act more as a single layer, rather than many sections.

I simply don't believe that happens to any significant extent, and because we don't promote products that don't have a clearly defined advantage, we don't promote sealant use any longer in this specific application. I've thought about this for years, have yet to see any data or theory that refutes my position, so we don't advocate the sealant, and are in the process of pulling the sealant reference from our illustrations.

Keep in mind we sell sealant, and we are not recommending it in this application. Certainly no harm in using it.

And in the same thread, comes the suggestion that standard "50 year caulk" works just as well:
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Originally Posted by tlogan6797 View Post

Unless something has changed in the, ah, umm, SEVEN years since I've been working on my room, regular old 50-year caulk works as well as "acoustic sealant."

But like I said, the majority of talk about products like SilenSeal is that it's necessary and worth the extra cost (at least twice, based on some quick research).

What are people's thoughts on that? Is there some solid reasoning or evidence that suggests that the dedicated acoustic sealants are worth the extra money?
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post #78 of 519 Old 02-04-2014, 07:28 PM
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50-year-caulk
is
acoustic sealant.

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post #79 of 519 Old 02-04-2014, 08:15 PM - Thread Starter
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50-year-caulk
is
acoustic sealant.

Okay. It's not advertised as such. I was looking at DAP Dynaflex 230, which claims to be permanently flexible and with a 50 year guarantee. Nowhere in any of their product descriptions do they mention its use as an acoustic sealant: http://www.dap.com/product_details.aspx?BrandID=14&SubcatID=3

I say that, because products like SilenSeal, QuietSeal, and Quiet Zone are specifically sold as being an acoustic sealant... and with a price to match.

I feel like I'm missing a key bit of info, here. What is it?
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post #80 of 519 Old 02-04-2014, 09:13 PM
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My contractor used PL400 between the layers of 5/8" drywall without discussing it with me.
I'd assume this is the exact opposite of what you want.
Please clarify.
I'd add I'm now considering a third layer and two tubes green glue per sheet.

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post #81 of 519 Old 02-04-2014, 11:53 PM
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Quote:
Originally Posted by granroth View Post

I was looking at DAP Dynaflex 230, which claims to be permanently flexible and with a 50 year guarantee. Nowhere in any of their product descriptions do they mention its use as an acoustic sealant: http://www.dap.com/product_details.aspx?BrandID=14&SubcatID=3
I don't know about that one.
I usually look for "acoustical" or "butyl".
The cheapest used to be "USB Acoustical Sealant".

An old thread, listing a bunch of caulk available at the time:
http://www.avsforum.com/t/765365/who-makes-acoustical-caulk#post_9123992

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Originally Posted by brwsaw View Post

My contractor used PL400 between the layers of 5/8" drywall without discussing it with me.
I'd assume this is the exact opposite of what you want.
I vaguely remember some experiments about this -- using glue to increase the stiffness of the wall.
I don't recall if it lowered the coincidence dip frequency (not good), or made no difference whatsoever (waste of money).
I think there was a theoretical drop in coincidence dip frequency, and a drop of about 2 STC points in STC50-STC60 walls, when gluing a wall with a traditional adhesive (PL Premium, Liquid Nails, contact cement).
In any event I don't think it's a crisis.

Green Glue is much better (good), because green glue lowers the resonance dip and coincidence dip amplitude, via damping.

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Quote:
Originally Posted by BasementBob View Post

I vaguely remember some experiments about this -- using glue to increase the stiffness of the wall.
I don't recall if it lowered the coincidence dip frequency (not good), or made no difference whatsoever (waste of money).
I think there was a theoretical drop in coincidence dip frequency, and a drop of about 2 STC points in STC50-STC60 walls, when gluing a wall with a traditional adhesive (PL Premium, Liquid Nails, contact cement).
In any event I don't think it's a crisis.

Green Glue is much better (good), because green glue lowers the resonance dip and coincidence dip amplitude, via damping.

Well, crisis or not the drywall is up so it is what it is.
All things considered I just want to get into the room.

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post #84 of 519 Old 02-05-2014, 08:46 AM
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I went through two cases of acoustical caulk purchased from the building supply company drywall division my builder used. The running joke during my build if we did not cut something as accurate as we would like was "nothing that caulk wouldn't fix"
http://www.avsforum.com/t/1468993/the-retirement-dream-home-theater/30#post_23281085

you can see front side of tube in this shot

I also insured that my drywall and OSB on the walls were sitting on the pink 1/8” thick roll of insulation designed to go under the wall plate to decouple the floor from the walls. Which I then trimmed after the drywall was in and then caulked between floor and drywall. I also caulked every hole that a wire came through just not shown here. These wires actually went into the stage so never really entered the room so to speak but I still caulked them.

I also caulked below in the garage. Basically if there was a crack or hole there was caulk in it. If I drilled any size hole for some CAT 6 or 12 GA or speaker wire caulk from both sides. I caulked between the sheets of OSB on the walls, ceiling and flooring. I actually ran a line of caulk in the grove of the second layer of 3/4" T&G flooring as seen in the link below. Everything and anything I did I put in the caulk. For the price I figured why not. Did it help I don’t know but I do know the sound proofing in my room is outstanding. Just have to finish the door.
20130601_202529.jpg
Someone asked me in my build about sound proofing my floor since I am on second floor here is my summary
http://www.avsforum.com/t/1468993/the-retirement-dream-home-theater/330#post_24276518
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Amazing thread, thanks for your work - much appreciated. TU
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post #86 of 519 Old 02-05-2014, 05:57 PM - Thread Starter
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Oh, sweet! Tons of great info in your post and also in the rest of that thread.

Let me summarize: when we refer to acoustical caulk, we are mostly referring to caulk that will not shrink over time. This is where the "50 year caulk" comes into play -- those types of caulk are guaranteed to not shrink for 50 years, which is as good as it's going to get. Why don't we want it to shrink? Because if it does, then now we've lost the entire advantage of caulking in the first place, since there is now a gap where there wasn't before! There's nothing really magical about "acoustical caulk" other than the ability to not shrink.

I'm going to quote this post, because it's right to the point and is far more persuasive than I could ever be:
Quote:
Originally Posted by Brian Ravnaas View Post

Tremco Acoustic sealant is generally available locally and is really flexible, gooey, oozy, stretchy, and all of those. Its solvent based and harder to work with as its tough to squeeze out of the tubes. From a theoretical-properties standpoint, its probably the best widely available acoustical sealant. Its 6 bucks or so in 29 oz tubes here.


The USG sealant is easier to work with and water based and generally a little cheaper. Other sealants are available as well in both solvent and water based, i certainly am not intimately familiar with them all and could not say "best, next best, worst, etc."


a lot of 50 year caulks are more flexible than a lot of water based "acoustical sealants", and in general latex sealants do contain the heavy fillers that are advantageous when covering large cracks, etc.


Sealants can, if their properties are right, add a bit of damping to a wall. Not enough to matter much, just a tiny bit at the coincidence dip, which for theater construction shouldn't be the primary concern. In a wall with even the tiniest dab of Green Glue, this small amount of damping doesn't mean anything because the GG supplies much more than any caulk to hope to.


On walls where drywall is screwed right up to the studs, the flexibility of the sealant won't have much effect on the behavior at all because the edge of the drywall is already rigidly constrained by the screws.


On walls - clips and resilient channel - where one edge of the wall is "free" to move, a more flexible sealant may (or may not, i've never seen a test to outline this) have advantages.


The most important thing is that you seal the wall. I can't imagine any situation where i'd be happier with 1 bead of an esoteric (often just repackaged name-brand stuff with a new label) sealant -vs- 3 of something cheap. Better yet, 5 of something really cheap.


A seal is 10^90th important, but how one attains it on the vast majority of walls is far less important.


GGCos recommendations are just based on our experiences in field and lab tests and permusing what precious little data we have ever found. USG once compared their sealant to a very ideal putty type material, and found essentially no difference save at the high frequency end of things at the coincidence dip.

Later on, Brian says "I don't feel that all of the acoustical sealants sold necessarily have any advantage over normal old boring caulks available everywhere" and finishes with "You folks can hold me to that when the day comes that GGCo releases a sealant.". I find that a little funny because doesn't GGCo produce SilenSeal? After Brian sold it, likely.

Anyway, part of my reasons for being so curious about it (other than being a very curious fellow by nature) is that acoustical caulk seemed to be so much more expensive than "normal" caulk. Bob, your post showed that that's not necessarily true. I did some searches for OSI SC-175 and discovered that Home Depot is selling cases online for 23 cents per ounce. That's half the cost of the DAP caulk I linked to earlier. Not bad at all!
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post #87 of 519 Old 02-05-2014, 06:05 PM - Thread Starter
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Quote:
Originally Posted by cw5billwade View Post

I went through two cases of acoustical caulk purchased from the building supply company drywall division my builder used. The running joke during my build if we did not cut something as accurate as we would like was "nothing that caulk wouldn't fix"

I've often said, "the world is built on caulk and shims." Heh.
Quote:
Originally Posted by cw5billwade View Post

Someone asked me in my build about sound proofing my floor since I am on second floor here is my summary
http://www.avsforum.com/t/1468993/the-retirement-dream-home-theater/330#post_24276518

That's great! That goes really well with the above discussion on soundproofing a floor from below. You are nailing down how to do it when you have access above.
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post #88 of 519 Old 02-05-2014, 08:11 PM
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I'm curious about something you might be able to answer.
My local supply guy asked me to consider using drywall in the T bar instead of the panels.
While considering it I though about the potential for drywall dust falling once installed and wondered about using an acoustic caulk around each edge to seal the seams (lift the panel, caulk around the topside of the lip, set the panel back down, tape all pieces first if necessary).
I'm pretty sure I don't want to go with the drywall in the T bar option (5/8" drywall is about a third of the cost and weighs more) but am still wondering about the potential of the acoustic sealant between the T bar and ceiling tile.
Is it worth while and would you do it? If you were in my position (not being able to hang drywall from the ceiling) which would you have installed?

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post #89 of 519 Old 02-05-2014, 10:28 PM
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brwsaw:

By 't bar' I presume you mean ceiling t-bar, used to hang acoustic ceiling tiles.

I don't know of anyone who's tried to do soundproofing with t-bar.

I'd be concerned that:
- the t-bar isn't strong enough for drywall. Home Depot's are probably not designed for that kind of weight. If it didn't break outright, the wire holding it up might unravel. There is t-bar on the market that's designed for drywall, usually thicker and I think with nail mounts rather than wire ties holding it up.
- to get the drywall up there, you need a bit of room around the drywall. Seems to me that air gap, and the steel t-bar itself, would allow noise to go through, negating much of the benefit of the drywall from a sound transmission loss point of view.

I'm reminded of the rule of thumb in the sound isolation world: "if you're inventing it, it's probably wrong."
Stick with what people with hundred million dollar research labs have tested and approved, and do it that way. If you're going to put drywall on the ceiling, screw it and green glue it. (maybe with room-in-a-room, or RSIC-1 clips)

If your t-bar panels are mostly (80% of them) light acoustic panels (possibly with R13 fluffy fiberglass above a rigid fiberglass panel) for absorption reasons, and you have a couple of drywall reflector panels for different acoustic reasons, that's one thing. But if your doing this for soundproofing, I'd stick with 4'x8' drywall panels and something traditional to hold them up with -- but you intimated that you're unable to do that for some reason.

The traditional reasons for going with t-bar is for
- acoustical absorption, and/or
- access to what's above the t-bar (pipes/wires/hvac, shut off valves, junction boxes), and/or
- quick installation

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post #90 of 519 Old 02-06-2014, 08:36 AM
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Yep and yep.
Low ceiling, heavy foot steps above, plumbing etc.
I've been told drywall is used in commercial installations in t-bar grids.
I'm set against it, was curious about the potential benefits of adding the acoustic caulk.
I will have 2 air gaps, 1 x 2" above the t-bar and 1 x 3" between batts of 3" insulation.
Sound proof is not possible, less sound transfer was the goal.
I measured the sound transfer between all the rooms before we installed the insulation and will re run the same tests after the T bar is installed.
It just has to be better than it was.
For another $100 bucks, if it would make any difference what so ever I would just do it (all edges, all tiles). No difference, I won't bother.
Now my next room will be much larger/taller and will be a room with in a room.
For now I'm stuck with the room I am fondly calling the "penalty box", when the wife says to go away, nuff said...gone.

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