Acoustic sealant: Acrylic vs. Neutral

[callaghan]

Hi to all , considering that here in Italy it's not that easy to find some of the brands of acoustic sealant that are quite popular in the forum I've made a little search and was wondering if anyone would like to comment on this.

Roughly there's 4 main types of popular sealants, ACETIC, ACRYLIC, NEUTRAL and BUTYL (hope I haven't missed any).
I've heard that ACETIC silicone is not ok (hardens too much right?).

However after searching and contacting various customer supports I found out that some say that NEUTRAL curing (known as neutral curing or pure silicone) shrinks less, hardens less and stays more elastic/flexible than ACRYLIC caulk over the years. Probably that is also due to the fact that ACRYLIC is more plastic and less elastic than the NEUTRAL one.

A popular silicone brand here in Italy suggests that the NEUTRAL one should be more flexible than the ACRYLIC. And regarding BUTYL it suggests that it's quite flexible but for joints that move more than 5% again NEUTRAL is better.

The GE Silicone II (NEUTRAL) site, the one that's much appreciated by Rod, states as follows:
"Silicone (GE Silicone II) stretches and compresses with joint movement as a house moves and settles. It remains permanently flexible and does not harden over time, which causes acrylic caulk to break—again, leaving cracks and gaps for air and water to pass."

However Auralex Stopgap (quite expensive I must say) and OSI SC-175 are both water based (ACRYLIC?) and both seem to be considered very good as acoustic sealants.

If we could understand which of the 4 types is best for acoustic caulking maybe I might be able to save some bucks and choose not by the brand's name but simply by it's specs...

Thanks for your help!

Pat

[Soundman2020]

I think I'd go with what they are calling NEUTRAL: sounds like the right stuff.

The acrylic ones you mentioned are specifically design for acoustic sealing, it seems, so they most likely don't suffer from the problems that Rod measured for the cheaper ones.

Maybe you can try to find some samples of that NEUTRAL stuff that was put in place a few years ago, and see how flexible and rubbery it still is today. In a large building supply store where I live (Chile) they have some samples stuck to the shelves themselves, and those have been around for a while. Maybe there's a place like that in Italy?


- Stuart -

[Ro]

the thing with silicone and butyl sealants is that you can't paint it over. Do notice when painting sealant will change the properties of the sealant (regardless of the type used).

You mostly need to care about the shrink level involved, you don't want "cracks". Preferably stays flexible, tho that's not a big deal on rigid structures (walls for example).

Since you're gonna use A LOT of sealant (prolly ten times more than you think) you should check your budget. The stopgap comes in large tubes, hence the price perhaps.

did I mention you're gonna use a LOT of sealant?

[callaghan]

I think I'd go with what they are calling NEUTRAL: sounds like the right stuff.

Dear Stuart thanks for answering , how are things over there in Chile? Yes I guess that the WATER BASED (ACRYLIC?) Stopgap and OSI SC-175 are specifically designed for the purpose so they have different specs from the normal ACRYLIC ones.
Unfortunately I could not find any "weathered" sample to look at. Please have a look at the table below and tell me what you think about it...

You mostly need to care about the shrink level involved, you don't want "cracks". Preferably stays flexible, tho that's not a big deal on rigid structures (walls for example).

Dear Ro thanks for your help again, according to the table below and considering what you've said about the importance of not shrinking over time it looks like the NEUTRAL is the best one, also it is rated with the highest flexibility of all so I think the choice is quite easy there. Regarding the fact that it's not paintable it is luckily not an issue for me.. And, do you think I should use a LOT?


This is a table I've found on all the different families of caulks and sealants divided by curing system. The first one at the top is the NEUTRAL one, ACRYLIC is the 4th, then BUTYL and ACETIC is the last one.

different caulks and sealants.jpeg

Anyone knows about any acoustic-wise downsides of the NEUTRAL curing silicones?

Thanks again guys

Pat

[Ro]

The silicone looks cool, but what's its density? A colored acrylic sealant typically has a density twice the density of gypsum, about 1200 kg/m3. Since you're gonna fill about 50% of the gap, it'll nicely fit your mass walls.
If that (neutral) silicone is about the same density then I'd say go for it. Pay attention to the curing time needed.

[callaghan]

uhm... thanks Ro, maybe you found a weak spot , I checked a few brands and average density of water based ACRYLIC is 1,50/1,60 g/cm3, while average density of pure silicone NEUTRAL is 1,02/1,25 g/cm3, ACETIC even slightly less than that.

I wish I could know GE Silicone II's (NEUTRAL) density but that piece of data is not present in the tech sheet... Nor could I find the density of the two water based ones, Stopgap and OSI SC.175...

Do you think that might be a problem? The problem is that ACRYLIC is denser, but it shrinks a lot, while NEUTRAL does not shrink...
Curing time is not an issue for me, I can wait as long as it needs.

What do you think?