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PostPosted: Tue Jun 19, 2018 5:26 pm 
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Hi Guys,

In a different thread Stuart says you "CANNOT" simply nail plasterboard used to beef up an outer leaf between the studs:

Quote:
..."beef up" the outer leaf, by placing strips of that in between the studs, up tightly against the OSB that is currently your outer leaf. That adds an extra layer to the "sandwich" ... which means that you have a LOT more mass on your outer leaf, which is good. There's a special technique for attaching that drywall: you CANNOT simply nail through it into the OSB! And you cannot glue it, either... When you are ready to do that, ask, and we'll explain


Why Is this? My plan was this: screw my 15mm plasterboard on to my 18mm OSB with 30mm screws. Then caulk around the edges.

Seems ok to me...

What am I missing?


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PostPosted: Tue Jun 19, 2018 5:40 pm 
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Keeping the pieces independent from one another allows them each to move/vibrate on their own, yet still act as a single mass, acoustically. It increases it's effectiveness. You CAN glue and screw them together, but again you will lose some performance.

Ideally, you should have Green Glue Compound in between the layers and hold the beef up layers up against the existing sheathing by tacking cleats onto the studs. This, along with good sealant around all edges, will give you the best performance.

Greg

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PostPosted: Wed Jun 20, 2018 2:16 am 
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Adding to what Greg said: If you screw and/or glue two pieces of mass together, they act as one individual mass which has a LOWER coincidence dip frequency, thus degrading isolation in the mid range. The rigidity (stiffness) is also higher, thus degrading isolation in the very low frequencies. Because Green Glue is not actually "glue", but rather a constrained layer damping compound, it does not create these problems. It joins the layers, yes, but it does so with a resilient, soft, flexible "joint", which allows the two layers to still move independently of each other, instead of as a solid "lump", which is what you would get with other glues.

- Stuart -

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PostPosted: Sat Jun 23, 2018 6:32 am 
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Thanks for the info guys. When you say cleats what do you mean? Have you got an image? Would screwing blocks of batton to the studs around the edge against the plasterboard achieve the desired result?

Thanks,
Dan


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PostPosted: Sat Jun 23, 2018 7:13 am 
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Quote:
When you say cleats what do you mean? Have you got an image?

I don't have an image handy, but it can be anything really. It could be a little rectangle of OSB just screwed into the stud. Scraps are fine. As long as it's strong and anchored to the stud in order to provide pressure against your beef up material, I think that's all that matters.

Greg

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PostPosted: Sat Jun 23, 2018 8:16 am 
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Gregwor wrote:
I don't have an image handy, but it can be anything really. It could be a little rectangle of OSB just screwed into the stud. Scraps are fine. As long as it's strong and anchored to the stud in order to provide pressure against your beef up material, I think that's all that matters.

Greg


Ah! That makes sense. That's very little extra effort over screwing them directly so I'll do that instead!

The weekend should hopefully have more progress on the build.

Thanks for your help again!

Dan


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PostPosted: Sun Jun 24, 2018 7:55 am 
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Quote:
When you say cleats what do you mean? Have you got an image?

Here's a thread I found that has some amazing cleats. They're too nice looking to be hidden! They're also custom made/fit rather than just scrap pieces like I suggested. Anyway, I thought this would suffice as an image as you requested!

Super fancy cleats!

Greg

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PostPosted: Mon Jun 25, 2018 4:19 am 
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Soundman2020 wrote:
Adding to what Greg said: If you screw and/or glue two pieces of mass together, they act as one individual mass which has a LOWER coincidence dip frequency, thus degrading isolation in the mid range. The rigidity (stiffness) is also higher, thus degrading isolation in the very low frequencies. Because Green Glue is not actually "glue", but rather a constrained layer damping compound, it does not create these problems. It joins the layers, yes, but it does so with a resilient, soft, flexible "joint", which allows the two layers to still move independently of each other, instead of as a solid "lump", which is what you would get with other glues.


I hadn't heard it put quite like this before, but it makes sense. I was wondering though, how does TecSound come in to play in this equation? It has mass (far more than GG) but is also soft and flexible, with no real rigidity to speak of, so are you not getting some benefit there? Or because it's 'mass', is any benefit negated?


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PostPosted: Mon Jun 25, 2018 1:14 pm 
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Quote:
how does TecSound come in to play in this equation?
To be honest, I really can't say as there is no acoustic data that I could find on it, from independent acoustic laboratories. All I found is a dubious Rw graph but with no source cited, but nothing at all when used as a CLD. So I'd take the claims with a very large grain of salt. From what I can see, it is similar to MLV but with adhesive backing, so I would expect that it acts more or less like MLV. It even costs the same, with most suppliers ... Hmmmm....

Quote:
It has mass (far more than GG)
Not really. The 4mm stuff has the same mass as 16mm drywall. Yes the DENSITY is 4 times higher, but in typical applications the MASS is the same, since you'd never use 16mm thick TecSound. They don't even make it that thick. The advantage is that you can have a thinner leaf with the same mass. That might or might not be a big deal. For example, if you built a leaf with 3 layers of 16mm drywall, the total thickness would be 48mm, but if you built it with 2 layers of drywall and a layer of Tecsound100 in between, it would have the same mass and be only 36mm thick and still have the same mass. So if you really needed the extra 12mm, I suppose that would be a plus.

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but is also soft and flexible,
True, and they CLAIM it acts as a CLD, but provide no data at all to support that claim. Maybe I just missed it in my search, but you'd think that if this really did provide major CLD benefits, they would feature the test results on the front page, in 90 point text.... But they don't. Hmmmmm....

If you compare the cost of using Green Glue vs. the cost if using Tecsound100, I think you'll find substantial savings with Green Glue, even considering that Green Glue is already rather expensive. Even cheaper still, would be no Green Glue and one extra layer of drywall, which will give you about the same isolation.

Quote:
Or because it's 'mass', is any benefit negated?
Not necessarily. A product can have both high mass and also exhibit good damping. For example, the density (mass) of Green Glue is around 3 to 4 times that of drywall... yet it damps very well.

To determine if Tecsound has better performance than Green Glue, you'd have to compare "apples to apples": Search the internet for acoustic test reports that are comparable, such as complete wall assemblies built with the same materials and dimensions, and the only difference bieng that one has GG as the CLD while the other as Teecsound as the CLD. My guess is that GG would be considerably better. If that were not the case, then BOTH companies would be comparing their products to each other. Yet they don't... Hmmmmm... GG doesn't need to because it publishes extensive independent research reports in its products, available for comparison against all other products. Tecsound does not seem to publish that information, so it isn't possible to compare.... Hmmm....

Caveat Emptor!


- Stuart -

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