Do Not Use Green Glue To Soundproof
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Yup, I said it. I am taking a stance on green glue and I do not use it in any of my studio designs. In this article I will make the argument why not.
1) Reason 1: The Added Cost
First, Green Glue costs a ton of money and most home studios don't have big budgets.
A soundproof wall typically uses two layers of 5/8" (16mm) drywall on either side of a double wall system. You can see the diagram below as an example. The cost of 1 layer of drywall is $17.87 here in the United States. That is $0.56 per square foot.
Now a pail of green glue costs $394.88 at Buildcorp Direct. They say that covers 380 Sq/ft. That means the cost of Green Glue is $1.04 per Sq/ft. At The Soundproofing Company a 5 gallon pail of Green Glue costs $406.69 and covers 365 Sq/ft. That comes out to $1.11 Sq/ft. Also, remember the cost of the speed load gun to apply the green glue is around $65.
Now lets average those two costs. The average cost for Green Glue is then $1.08/SqFt. Remember, to that for smaller projects where you don't need a pail of Green Glue the cost will be higher.
Now, Green Glue on average costs $1.08/square foot. That means the cost of adding green glue is almost the same as adding two more layers of drywall to your wall. As I will talk about in the next section adding two layers of drywall will certainly be better than adding Green Glue.
Now you may say, well I could add Mass Loaded Vinyl instead of drywall or Green Glue. The answer would be that the cost would again be even more for MLV and I would argue not worth the added damping it provides.
5/8" drywall weights around 2.2 Lb/SqFt. MLV weighs 2 Lb/SqFt. The cost of 2 Lb MLV is $179.95 and covers 50 SqFt. That is $3.60 per square foot. That is six times the cost of drywall and over three times the cost of Green Glue. So when you want to build a studio for $15-20K why would you waste money on Green Glue and MLV when you could add more drywall for less money?
Now you are going to say, Wilson, but I don't have space for more drywall. My answer would be you will lose 5/8" of an inch on each wall. If you want to save that space and spend way more money doing it then go ahead, but it is not a logical conclusion in my opinion.
2) Reason #2 - Mass is better than damping
In soundproofing we have two systems that help with sound attenuation. The first is mass and the second is damping. Mass is most important because without mass you cannot stop sound, especially low frequencies. You cannot hang RockWool insulation and stop sound, just like you cannot hang MLV and hope to stop sound. Both of those substances, like Green Glue absorb sound through damping, which is the conversion of sound to heat through frictional or restrictive forces.
Mass on the other hand reflects sound. A solid concrete wall will reflect more sound than a wall with only drywall. Mass also reflects low frequencies better than damping alone. For this reason, it is always better to add mass first and damping second.
When you are on a budget you should add drywall before buying Green Glue. If you have a budget you should build heavier concrete walls over weaker drywall walls. Either way, you should not use Green Glue because it is an efficient use of your money.
3) Reason #3 - STC Ratings don't Go Below 125Hz
A big problem in the home recording studio market is that the STC ratings everyone focuses on don't even measure below 125Hz. They were designed to set standards to reduce the transfer of the human voice from room to room for commercial buildings and residential condos. They were not designed for recording studios.
Therefore, STC ratings are mostly useless when it comes to studio design. Shocking right? So what do you do. You use experience to guide decisions on how much isolation you need and you follow studio designers like myself not the big companies pitching you soundproofing products.
Philip Newell has a great quote in his book, "Recording Studio Design." He states,
"One would think that from the individual isolation figures of the individual isolation systems we would be able to calculate the total isolation, but there are interactions which make calculations difficult unless many other factors are known. " (Philip Richard Newell, 56)
Basically, to paraphrase, Newell is saying experience is key. STC ratings, forums, books and any other advice is only that and at the end of the day until you have built a few studios you don't know how things will work together because there are simply too many variables to test, calculate or predict fully.
Now, back to the STC ratings. If you look at Green Glue's STC ratings they will say that it is superior to two layers of drywall and that is true according to the test data, however, it is not necessarily superior to four layers of drywall because the added mass will help with those frequencies below 125Hz. Again, recording studios require experience and understanding beyond simple lab tests and STC reports.
4) Reason #4 - The Pros Do Not Use Green Glue
I have talked to three different studio designers and soundproofing professionals and none of them uses or recommends using Green Glue. I personally talked to Rod Gervais, the author of Home Recording Studio: Build it like the Pros and he said he no longer recommends Green Glue because Saint Gobain is said to have changed the ingredients since his initial testings. He recommends more layers of drywall or adding MLV if space is tight.
JH Brand, and I talked over zoom and he said he also does not use Green Glue in his studio designs. Philip Newell, the author of Home Recording Studio Design and one of the original studio designers from the 60's on never once mentions Green Glue in his over 700 page book on studio design.
Finally, I am working with a Soundproofing contractor with over 10 years of experience building soundproof rooms and he also said he doesn't use Green Glue and prefers other methods that are cheaper and better for sound isolation.
The fact that professionals in the field do not use Green Glue is further proof that this product is too expensive and possibly not even that useful for sound isolation.
5) Reason #5 - Green Glue Needs To Be Retested
It is not easy to find reliable test data on Green Glue, in fact Green Glue has removed all test data from their website in recent years. The last reliable test data done by the Green Glue company was done in 2011 as can be seen below from SoundMan2020's blog where he posted several lab results. (“Green Glue Test Results - Soundman2020 - Studio Design Forum”)
Notice this lab report was done by Saint Gobain. Saint Gobain acquired Green Glue from its owner, Brian Ravnaas back around 2010. Now, this is getting into some conspiracy theory territory, but I think it is worth mentioning in this argument. I had made a video touting that Green Glue is equivalent to four layers of drywall as is stated in Rod Gervais's book: Home Recording Studio: Build It Like the Pros. However, Rod emailed me after posting the video and said he no longer recommends using Green Glue. He said the reason was that when Ravnaas sold the company, Saint Gobain then changed the ingredients. Gervais made it clear that his testing done with Ravnaas was now in question and could not be trusted anymore.
I have reached out to Ravnaas many times to confirm this accusation, but have not gotten a response. It does make me question Green Glue's validity, especially in the hands of a mega corporation like Saint Gobain.
Second, Gervais and Ravnaas are not alone in accusing Green Glue and Saint Gobain of posting unfair or false test results. Serious Materials, the maker of Quietglue Pro, a direct competitor to Green Glue states that:
"Green Glue states that they had an STC 55 in 2005 and we should just take that and move on. To state this clearly: We have not been able to reproduce their results after spending considerable financial and people resources on testing in multiple independent labs with varying dry times out to 35 days." (“Green Glue Test Results - Soundman2020 - Studio Design Forum”)
My point here is to say that Saint Gobain needs to re-test Green Glue in a verified lab and show that it still lives up to its standards. I would also love to see a comparison of Green Glue in a double wall system, since most STC lab reports only show a single wall assembly. Again, Green Glue makes way more money off commercial building applications where the human voice is the main concern.
6) What about Carpet Glue?
If you search on Youtube about soundproofing and Green Glue you are bound to come across people saying carpet glue is the same consistency as Green Glue, but cheaper. I do not recommend using carpet glue, but if you want to experiment then carpet glue could be an option since it is far cheaper than Green Glue. However, based on my arguments above your best option is to add more mass to your wall before wasting time working with sticky carpet glue.
Conclusion
In conclusion Green Glue costs twice as much as adding one more layer of 5/8" drywall. Adding more mass to a wall will help you attenuate against low frequencies. While damping with Green Glue, MLV, Insulation, Carpet Glue or any other damping material will help, it still remains an expensive option when compared to simply adding more drywall. If you require high isolation and have the budget and space than I would always recommend two masonry walls with as big an air gap as possible.
Green Glue shows higher STC ratings, but remember STC ratings do not officially test below 125Hz. This makes this data largely irrelevant for home studio construction. Heavier walls will always lead to better attenuation at lower frequencies.
Then remember the professionals in the industry do not use Green Glue so why should you? Green Glue is a money maker for soundproofing stores and Saint Gobain, it is not the end all be all way to achieve great sound isolation.
Saint Gobain should re-test Green Glue and show that it still stands up to its competitors and other forms of sound isolation. I would be curious to see how a double wall wil three and four layers of 5/8" drywall compares to a double wall with two layers of drywall and Green Glue.
Green Glue competitors and options like carpet glue may be cheaper, but they still don't have the same benefits of adding more mass to the wall for less money. You can try carpet glue if you want to experiment, but there is not any reliable test data on its use.
For all of these reasons I do not think you need to use Green Glue to soundproof your room. If you want more isolation than two layers of 5/8" drywall then add another layer or two of drywall. If you don't want drywall or if you are worried about the coincidence effect then you could use plywood or OSB with a similar mass to 5/8" drywall. Either way you will save money and achieve better isolation by simply using basic construction materials like drywall and plywood.
Works Cited:
Gervais, Rod. Home Recording Studio: Build It Like The Pros. 2nd Edition, Course Technology Cengage Learning, 2011.
“Green Glue Test Results - Soundman2020 - Studio Design Forum.” Forum.digistar.cl, forum.digistar.cl/viewtopic.php?t=773. Accessed 28 Mar. 2024.
Philip Richard Newell. Recording Studio Design. New York ; London, Routledge, Taylor & Francis Group, 2017.
