Using green glue between 2 different materials?

[princeplanet]

I read often that for green glue to be effective, it really needs to be sandwiched between 2 layers of similar materials. But what if one layer is 25mm particle board and the other is 25mm cement tiles? This is for a floor (part of a RWAR ) that is trying to attenuate low frequencies through a 125mm concrete slab. The air gap (insul filled) will be 100mm, and the 2 layers will be resting on engineered rubber pads (for optimal deflection).

Any thoughts?

pp

[DanDan]

I would focus on optimising the floor suspension.

[John Steel]

I read often that for green glue to be effective, it really needs to be sandwiched between 2 layers of similar materials.

Interesting - can you share some links with us please? Best wishes, John.

[princeplanet]

I read often that for green glue to be effective, it really needs to be sandwiched between 2 layers of similar materials.

Interesting - can you share some links with us please? Best wishes, John.

Try the Green Glue FAQ for a start. I know I've read there and elsewhere that GG works best with similar densities, but not sure if that could be takes as materials of similar "stiffness". Any thoughts might be helpful.

[John Steel]

Thanks for your suggestion - I have read the FAQs on www.greengluecompany.com as well as their design guide and test data. Where as most of the examples given on the site tend to refer to double (or sometimes triple) layers of similar materials, I couldn’t find any specific mention of reduced effectiveness when GG is used between layers of different densities, except if they’re flexible:
“The compound will not work in contact with flexible, low surface energy, or non-stick materials. The compound will not work in direct contact with:  Cork, plastics, copper, bronze, zinc, MLV (Mass Loaded Vinyl), and Plasticized materials among others. It will not work in contact with flexible materials.”
Density is mentioned in the FAQs within a context of more being better -
“As mass plays an important role in soundproofing, we recommend using the thickest layer of drywall available . . . The same rules apply to other building materials such as plywood and OSB.”
“Green Glue Noiseproofing Compound is used between two layers of building materials – typically drywall, OSB, MDF, cement board, or plywood. So long as two of the layers are flat, rigid . . . are easy to stick to and at least one allows moisture to pass through then the Noiseproofing Compound will perform well.”
Unless I’m missing something, this suggests that GG will work between any two rigid layers. This is significant to me since I’ve used 18mm OSB and 12.5mm cement board with GG in between. I could easily ‘beef up’ the OSB side of the combination but I’d rather not if it can be avoided!
Best wishes, John.

[princeplanet]

Thanks for your suggestion - I have read the FAQs on http://www.greengluecompany.com as well as their design guide and test data. Where as most of the examples given on the site tend to refer to double (or sometimes triple) layers of similar materials, I couldn’t find any specific mention of reduced effectiveness when GG is used between layers of different densities, except if they’re flexible:
“The compound will not work in contact with flexible, low surface energy, or non-stick materials. The compound will not work in direct contact with:  Cork, plastics, copper, bronze, zinc, MLV (Mass Loaded Vinyl), and Plasticized materials among others. It will not work in contact with flexible materials.”
Density is mentioned in the FAQs within a context of more being better -
“As mass plays an important role in soundproofing, we recommend using the thickest layer of drywall available . . . The same rules apply to other building materials such as plywood and OSB.”
“Green Glue Noiseproofing Compound is used between two layers of building materials – typically drywall, OSB, MDF, cement board, or plywood. So long as two of the layers are flat, rigid . . . are easy to stick to and at least one allows moisture to pass through then the Noiseproofing Compound will perform well.”
Unless I’m missing something, this suggests that GG will work between any two rigid layers. This is significant to me since I’ve used 18mm OSB and 12.5mm cement board with GG in between. I could easily ‘beef up’ the OSB side of the combination but I’d rather not if it can be avoided!
Best wishes, John.

How well did it work out? I'm thinking to use GG b/n 25mm particle board and 25mm cement pavers in a floating floor. I'm concerned that effectiveness might be reduced owing to the different materials and their densities, but also their sizes, the cement pavers will be perhaps a small as 400mm x 400mm. If I was sure to get increased TL for low frequencies using the GG I would not hesitate, but if we're talking only a dB or 2, then it's probably a waste of time and $ ... ?

[gullfo]

in general, GG and equiv are like added another layer of the drywall - with a touch of LF damping and much less weight. so you should see more than a db or two increased TL from the mass BUT (there's always a big but) depending on the placement, materials, and structural contact/conduction etc will ultimately determine the overall TL. the Green Glue folks can really only provide the results of their testing on "standard" wall and ceiling configurations. they might have some anecdotal info from customers regarding other construction configurations and materials so it can't hurt to reach out and ask for their experience in this regard.

[John Steel]

. . . it can't hurt to reach out and ask for their experience in this regard.

Absolutely.

How well did it work out?

Slightly too soon to tell as the outer leaf isn't complete.