My experience with Green Glue

[eric_desart]

rod,

without speaking about the use of damping, but just compring mvl versus bitume foil:
this is tested and compared a lot.

in the industry one uses much more bitume based foils (which are extremely comparable with this roofing felt) for damping.

the main difference is that one add minerals or whatever to bitume foil to increase density.
but the same happens for mvl.

at room temperure one can safely state that mvl and good bitume foil are interchangeable with even slight advantage for the bitume foil. (just in general)

the main reason that one uses pvc (most mvl, but not all as jeff from auralex pointed out) is that it's better at very low temperatures. damping of such foils is frequency and very temperature dependent.

as such the choise is more defined by mechanical and fire properties. and how to fix them (pvc isn't the easiest material to glue either in large surfaces). both excist in self adhesive versions to solve gluing problems.

this is more for brian (me not a chemist remember) but pvc doesn't or hardly burns from nature (therefore it's used as welding screens were even red hot particles will not damage the foil but reflect as waterdrops) but when it burns by external fire source the chloor gass is poisened.

it depends on the types but from a cost effective point of view bitume foil is a VERY valid alternative for mvl, certainly for normal inside temperatures, even to rather low.

i think if one should compare damping foil for industrial use in quantity the bitume foil wins clearly.

bitume like foils (really looking and feeling and being like roofing felt) is used in enormous amounts in industrial sound insulation as eg the ducting in the chemical industry and power plants.
one such project can cover many thousands m2 of insulation.

in function of fire properties i leave it to brian to explain, but gypsum board uses a lot of heat energy to alter first his structure (releasing water , don't know correct words), so it takes a long time before it transmits this heat to the other side. as such gysumboard is a rather good firescreen for bitume.

[Rod Gervais]

Eric,

With all due respect, if I understand previous conversations regarding this issue - the real advantage to the use of the bitumens would be added mass.

If that is the case then the gain for a typical roofing felt (30#) would only be .3 psf. Which I do not see as a gain versus normal construction.

It's a different story if one is working with a bitumen product meant for the job - where (as you noted) the main difference is that one add minerals or whatever to bitume foil to increase density.

But to add a layer of .3psf material when the only real gain is the mass makes no sense to me.

What am I missing?

Sincerely,

Rod

[eric_desart]

hello rod,

if you read my first sentence you'll notice i compare between mvl and bitumen foil, saying i'm not discussing the use of it.

brian gave somewhere the formula in this thread showing the increase in insulation versus increased damping (the 10 log(new damping over original damping).

this means that materials with higher internal damping will show a lower vibration level, hence a higher tl for the same mass.

if you compare the tl values of mvl versus the tl values of gypsum board you notice that the mvl has higher tl values when judged versus mass.

as such damping is an intrinsic variable in prognoses models.

in fact compare this damped or undamped vibration level in a panel with the rt60 of a room.

when you add absorption in a room, assuming you have a source with a fixed level, then the pressure level in the room will diminish while the source still have exactly the same excitation force.
by lowering this rt60, you lower the cumul of the added energy in the room.

this however isn't much.
the formula is exactly the same as for vibration.
the level in the room (in diffuse field = averaged level) diminishes with 10 log (A1/Ao) where A1 is the new rt60 and Ao the former one. (can be expressed in rt or absortion).

now imagine this pressure level to be the vibration level in this panel.

back to damping gypsumboard walls.

this whole thing is a matter of ratios. while mvl is a more efficient mass as gypsum board itself, it's expensive versus the added value.
by combining such materials with others you get e new combination with a higher internal damping.

but other factors influence tl as well.

rod, i come back on this later or brian can jump in, i'm more busy searching keys with my left finger than with the content.

what i mean is: it all depends in how far one can increase damping of a whole construction.

brian with his gg brought it to an extreme, which indeed makes it worth looking into for drywalls.

you have just increased damping and contrained layer damping (as brian uses)

more later:
anyhow there are applications where it's usefull (laminated glass is such an example) in lightweight steel and alu it's used a lot.

note: this expose is not meant to defend the standard use of mvl, nor bitumen in walls. my post was meant to set them versus one another.
in the indudtry we prefer bitumen foils in different versions (which is not at all at the expense of acoustic quality) and select only pvc when needed for mechanical, temperature or fire properties.

the added minerals to increase density is nothing magic, but a cheap manner to increase mass of this foil which guarantees it a better ratio versus the material it is glued upon.

compare with a singing crystal glass,
if a fly goes to rest on it, the glass continuous singing (the fly's brain, if it has one, gets scrambled), press your finger against this glass (act as damper) and the singing stops.

therefore bitumen foil on a 0.7 mm steelsheet will do a lot (above just increasing mass), the same foil on a brick wall will do close to nothing.

it's a matter of ratios: in how far can a foil influence such ratios, taken into account that a construction in itself already will increase damping. as such the comparison with naked theoretical materials isn't really valid.
take a piece of flat hanging steelsheet and knock on it: it sounds as a gong. no real live construction from the same steelsheet will sound like that.
now glue a small piece of bitumen foil on this freehanging piece of steelsheet, knock again on it. what you hear now is dead. this has nothing to do with increased mass but with the increased damping which shortens RT60 in the steelsheet itself giving it a better tl at the same time.

i repeat, i do not defend the standard use in drywall in function of cost effectiveness.
it's not for nothing that one doesn't find objective comparisons published on the net.
as such i believe we are on the same wavelength.

[z60611]

(Here I definitately don't know what I'm talking about, might be apples and oranges, just what I've observed in two places while looking for other stuff)

In Ontario Canada, I can use in an underground basement wall (2.41 guide for housing) anything that conforms to these standards (9.13.2.1 OBC):
a) CAN/CGSB-37.1M "Chemical emulsified Type, Emulsified Asphalt for Dampproofing",
b) CAN=CGSB-37.2-M "Emulsified Asphalt, Mineral Colloid Type, Unfilled, for dampproofing and Waterproofing and for Roof Coatings"
c) CGSB 37-GP-6Ma, "Asphalt, Cutback, Unfilled, for Dampproofing"
d) CAN/CGSB-37.16M "Filled, Cutback Asphalt for Dampproofing and Waterproofing"
e) CGSB 37-GP56M, "Membrane, Modified, Bituminous, Prefabricated and Reinforced for Roofing"
f) CGSB 37-GP-18Ma "Tar, Cutback, Unfilled, for Dampproofing"
g) CAN/CGSB-51.34-M "Vapour Barrier, Polyethyline Sheet, for use in Building Construction"
h) CSA A123.4 "Bitumen for Use in Construction of Built-up Roof Coverings and Dampproofing and Waterproofing Systems."

Home depot sells roofing paper (EMCO RR401)that conforms to "CSA A123.2M Type M" and another brand that conforms to "CSA A123.16 Type 1".

[Rod Gervais]

Home depot sells roofing paper (EMCO RR401)that conforms to "CSA A123.2M Type M" and another brand that conforms to "CSA A123.16 Type 1".

Z,

Dampproofing is (and you knew this - hence the apples and oranges quote) not the same as damping.

So this is great stuff to use as long as you want to keep things dry - and those materials conform to the standards used to specify the standards for their construction - but that has nothing to do with sound isolation.

Nice try though buddy ....... lol

Rod

[Brian R]

ok... but drywall won't get much cheaper in volume... at least here, drywall is more expensive when delivered by larger commercial distributors than when picked up yourself at home depot.

....

Greetings Brian.

That's not true in the UK. At least from my experience. Teh commrecial supplier price was much less than the 'home depot' price. Furthmoer muying in volume can save lots.

My drywall was dsicounted so much for the volume, that doing 7 layers cost about the same as doing 3 or 4 layers.

:)

Paul

p.s great thread, I'm silently following with interest :)

glad you like the thread, sorry folks to be away so long.

in Fargo, ND, today 4 skids (8000 lbs or whatever) of drywall delivered here would cost me $9.25/sheet. i could pick it up at home depot for $7-something a sheet.

later in the year both those prices will go up ~20%

i didn't ask about discounts if i purchased an immense quantity, like truckload.

[Brian R]

hi folks,

with respect to the use of bitumen/asphalt, or whatever you would like to call it, as a damping material for drywall assemblies, some things should be noted


first, putting a sheet of asphalt (or ANY other damping material) on top of drywall will result in a grossly bad cost/damping ratio.

damping material sitting on top of something is called "extensional" damping. extensional damping is massively inept/inefficient at damping thick/stiff/heavy structures. 5/8" drywall would constitute a structure far stiffer than is almost ever damped in this manner.

extensional dampign is used basically only on sheet metal, as was mentioned above. thin gauge sheet metal...


a sandwich damping assembly where the damping material is sandwiched between two "stiff" structures is a very different story. This is constrained layer damping, and this is capable of damping even 4" plate-steel. This assembly can raise the damping of a drywall construction to an impressive fraction of critical damping (depending, of course, on the success of the damping material).


now, extensional damping follows universally this simple rule: the more the merrier. the more extensional damping material you plop on the better the performance will get. more more more (all other things equal) will yield more more more


cut constrained layer damping is not so straightforward. take something like Green Glue. if you used more more more, performance will become worse, not better.

CLD is a bit of a precision thing, a thing that nearly MUST be engineered if truly good results are to be expected. Indeed, given optimized material and factor application conditions, you could create a highly effective CLD system with a very, very (few thousandths of an inch) thin damping layer, allowing the possibility of cost-effectiveness


for any given material to work well in a CLD system you have to have several factors aligned, including a system that supplies shear, a material that can be sheared at the relevant frequency/thickness/temperature/assembly, a material with a high loss factor, and a material with a shear modulus appropriate to the desired final system properties.

[Brian R]

to expand on that last point a bit... this lab has a material similar to Green Glue but with one tremendous advantage... it could be manufactured for a fraction of the price. another advantage is that it's superior across much of the relevant frequency range (high freq's), and nearly a match for GG at the important wall resonance frequencies - in a free lab panel without screws. Use screws on a wall assembled with this material and the reaction isn't good, performance suffers alot (Again mostly at low frequencies)

also, one mechanical property winds up being non-ideal, and performance further suffers as a result. the net result is a material that yields a few dB to a wall, not 7-10+

and hence it isn't a viable material. there is not remotely reason to believe that an extremely good asphalt sheet or mastic could be made. that these materials couldn't make a very good damping material for this application.

there is also not remotely reason to believe that any given assembly would yield significant results. for example, some (when glued in) bitumen sheets cause the same type of stiffening in the panel as liquid nails. others cause no stiffening. some yield mentionable levels of damping, some don't

to make an asphalt a good performer for a specific application would mean engineering it for a specific application, would mean it wouldn't be so cheap anymore (not that roofing rubber is really all that cheap)


anyway

[Brian R]

hello rod,

if you read my first sentence you'll notice i compare between mvl and bitumen foil, saying i'm not discussing the use of it.

brian gave somewhere the formula in this thread showing the increase in insulation versus increased damping (the 10 log(new damping over original damping).

this means that materials with higher internal damping will show a lower vibration level, hence a higher tl for the same mass.

.

that formula is applicable only to impact noise. the noise generated from repeated rapid striking of a surface... for airborne sound, that doesn't apply.

apologies for being unclear on that point

Brian

[Brian R]

gentlemen,

i apologize for my poor follow-ups to the considerable conversation in this thread. i've been away tending to green things, and will be away again until next week.

rod said above that he feared i'd stop posting... i wouldn't, rod, and i'm very grateful for the invitation you extended to join this forum some time ago.

take care guys,

Brian