What brand of fireblock caulk to buy?

[Quint]

What are some suggestions for a good brand/type of caulk to use for fireblock that remains un-hardened (maybe elastomeric is the more correct term?) once it has cured, or is otherwise suitable for fireblocking which will not mechanically couple the inner and outer leaves in the process? I've searched quite a bit here (yes, I looked in the reference area too) on the forum and have been surprised at the relative lack of discussion on this matter. Bottom line, I don't want to spend all this time building isolated, "room inside a room" assemblies and then ruin it by using a fireblock caulk that will transmit sound by mechanically coupling the inner and outer leaves.

Just to provide a little background, I will be applying a bead of fireblock caulk along the exposed edge of the rockwool which is sandwiched in between the inner and outer leaves where the walls meet the ceiling, just as is described in Rod's book. The fireblock caulk is necessary to prevent hot gas from passing all the way through the rockwool, again, as described in Rod's book. I should also mention that, whatever product(s) anyone may suggest, they need to meet commercial building standards and codes. I imagine residential standards on fireblock caulk are not as strict, though that would also be a discussion worth having for people who might read this thread and need to find out about a product which only needs to meet residential fireblock standards. But to be clear, I am looking for products that meet commercial standards.

Does anyone have any good recommendations? Does such a product even exist? In other words, does there exist a product which is sold/marketed as a commercial rated fireblock product which ALSO happens to have suitable acoustic properties, or is it necessary to purchase a product which is sold/marketed as an acoustic sealant type of product that ALSO just so happens to have the appropriate characteristics necessary to meet commercial fireblock standards? In either case, I need to find something that meets the fireblock AND non-coupling requirements.

As an example, I was looking at the 3M product below, but I can't find any in depth info on its final cured state or if it is suitable for use in a sound isolated assembly? The back of the tube says that it "dries to a firm, rubber-like solid". That's the most information I can find about its cured state. It also says it's latex based, which gives me pause, because, in my understanding, silicone based caulk is the type you want if you want a caulk that won't cure/harden to the point where it allows sound transfer through mechanical coupling of the inner and outer leaves. Anyway, here is the product below:

3M 10.1 fl. oz. Red Fire-Barrier Sealant Caulk CP 25WB Plus

Also, though it's a different kind of product, and I'm inclined to think it may not work or is intended for my stated application, I'm also curious about Great Stuff Fireblock. Maybe it would work in this scenario. Maybe not. I don't know. Anyway, here that product is:

Great Stuff Fireblock

Bottom line, I need to find a good fireblock caulk/foam/whatever that will meet my stated fireblock requirements while also not creating mechanical coupling between the inner and outer leaves. Thoughts? Thanks in advance for the help guys.

I'm here in the US, if that matters or might affect anyone's answers.

Here's an example of the type of fireblock system I'm talking about in the image below, though I'm unsure of whether the particular 3m fire caulk specified in that image would suffice.

[Quint]

Seriously,

I will pay someone who is qualified in these matters to give me advice on which caulk(s) will meet my needs. I need to know the answer to this question asap. It's holding everything up. Any takers?

[Gregwor]

I'd tell you if I knew the answer. I also would like to know!

I also want to know if I should use Green Glue sealant or LePage Acousti-Seal. The LePage is quite a bit cheaper.

Greg

[Quint]

I just edited my initial post to substitute the use of the word coupling instead of flanking. I realized that flanking may have not been the most appropriate word to use (but maybe it was?).

To be clear, I'm concerned with finding a fireblock caulk that won't mechanically couple the inner leave to the outer leave when applied at the fireblock seal, as I described in my initial post.

Thoughts?

[Quint]

Update:

I've also come across these fireblock caulks which state that they are elastomeric, though I have yet to test them to see how elastomeric they actually are:

https://www.homedepot.com/p/DAP-Fire-St ... /205030322

https://www.stifirestop.com/products/es ... p-sealant/

https://www.3m.com/3M/en_US/company-us/ ... 936&rt=rud

I've tested the following fireblock caulks below, and only the 3m CP 25wb+ seems to possibly remain pliable/elastomeric enough once it's cured, as the other two caulks seem too hard after curing to me, and would likely cause mechanical coupling between the inner and outer leaves. Here those three caulks are:

https://www.3m.com/3M/en_US/company-us/ ... 924&rt=rud

https://www.3m.com/3M/en_US/company-us/ ... 898&rt=rud

https://www.homedepot.com/p/3M-10-1-oz- ... /100390499

Anyway, I'm still totally unsure here what I should be using as the proper fireblock caulk. Some help on this would be greatly appreciated.

Also, I've updated my original post with an image depicting a fireblock system similar to what I'm trying to achieve. That same image is also below:

[Soundman2020]

You might be over-thinking this: Believe it or not, fire blocking does not necessarily have to be non-flammable! It just has to create an air barrier. The purpose is not so much to stop the flames from burning, but rather to prevent air from feeding the flames. You can use wood to create fire-blocking in most fire codes. Check your own local building code, since fire blocking regulations are very, very variable, but you will probably that ordinary siliconized-acrylic caulk or silicon sealant, which are non-flammable anyway, would be acceptable.

If your code does insist that you absolutely must use a "fire-blocking caulk", then you have no choice: go with whichever one you can find that is the most flexible after it has cured.

- Stuart -

[Quint]

You might be over-thinking this: Believe it or not, fire blocking does not necessarily have to be non-flammable! It just has to create an air barrier. The purpose is not so much to stop the flames from burning, but rather to prevent air from feeding the flames. You can use wood to create fire-blocking in most fire codes. Check your own local building code, since fire blocking regulations are very, very variable, but you will probably that ordinary siliconized-acrylic caulk or silicon sealant, which are non-flammable anyway, would be acceptable.

If your code does insist that you absolutely must use a "fire-blocking caulk", then you have no choice: go with whichever one you can find that is the most flexible after it has cured.

- Stuart -

I'll have to check on the code, but the city here is notorious about being difficult and not understanding the goals. It is actually Rod Gervais that has said on more than one occasion (on this forum, other forums, and his book) that you have to use an actual fire caulk. Believe me, I would be happy to just get away with using a much more flexible silicone caulk over the rockwool or, better yet, no caulk at all. But Rod knows code as well as anybody.

So just for discussions sake, if I were to forego using fire caulk and instead use a normal silicone caulk or acoustic caulk, what would be the best one to use, keeping in mind that I need to use a caulk which is the MOST flexible and will create the least amount of mechanical coupling between the leaves?

Thus far, I've been using GE Silicone II caulk everywhere, but that's just been for sealing joints and gaps, not for something like this. Would the GE Silicone II work for this application too, or is there something even better out there? Maybe Green Glue Sealant or some other acoustic caulk?

[Soundman2020]

I'll have to check on the code,

Maybe just call up the inspector and ask him personally!

Thus far, I've been using GE Silicone II caulk everywhere,

According to the data base, the flammability of that stuff is rated as "0" :

https://hpd.nlm.nih.gov/cgi-bin/househo ... d=13039025

So it is not flammable, and personally I don't see any issue there. But if your city is complicated, I would check with them, to be sure.

Would that work for this application too,

For the application, yes it would. It will do what you want it to do. However, if your local authorities don't approve of it, then you should uses something the do approve of.

Maybe Green Glue Sealant?

I love Green Glue compound! I do not love Green Glue sealant: it cracks as it dries if you make it a little too thick.


- Stuart -

[Quint]

I'll have to check on the code,

Maybe just call up the inspector and ask him personally!

Thus far, I've been using GE Silicone II caulk everywhere,

According to the data base, the flammability of that stuff is rated as "0" :

https://hpd.nlm.nih.gov/cgi-bin/househo ... d=13039025

So it is not flammable, and personally I don't see any issue there. But if your city is complicated, I would check with them, to be sure.

Would that work for this application too,

For the application, yes it would. It will do what you want it to do. However, if your local authorities don't approve of it, then you should uses something the do approve of.

Maybe Green Glue Sealant?

I love Green Glue compound! I do not love Green Glue sealant: it cracks as it dries if you make it a little too thick.


- Stuart -

What's an acoustic caulk that you would recommend for my situation, assuming that it would be acoustically superior to GE Silicone II? Or is GE Silicone II just as good as any acoustic caulk for my specific purposes?

[Gregwor]

Stuart,

I do not love Green Glue sealant: it cracks as it dries if you make it a little too thick.

The only other stuff that I can find (it's similar in price to GG... maybe a dollar a tube more expensive is the LePage PL Acousti-Seal
Here is the link to their page on it:
http://www.lepage.ca/en/lepage-products ... alant.html

Greg

[Quint]

I'll have to check on the code,

Maybe just call up the inspector and ask him personally!

Thus far, I've been using GE Silicone II caulk everywhere,

According to the data base, the flammability of that stuff is rated as "0" :

https://hpd.nlm.nih.gov/cgi-bin/househo ... d=13039025

So it is not flammable, and personally I don't see any issue there. But if your city is complicated, I would check with them, to be sure.

Would that work for this application too,

For the application, yes it would. It will do what you want it to do. However, if your local authorities don't approve of it, then you should uses something the do approve of.

Maybe Green Glue Sealant?

I love Green Glue compound! I do not love Green Glue sealant: it cracks as it dries if you make it a little too thick.


- Stuart -

So I just came across this site which does a great job of describing fireblocking versus draftstopping and what that all means in the context of the International Building Code (IBC).

https://www.buildingcci.com/blog/10-12- ... -draftstop

According to this site and the IBC, draftstopping is required to divide floor/ceiling cavities up into areas of no greater than 1,000 sq ft. The ceiling cavity above my booth is no where even close to that in size, so apparently draftstopping may not even be required for my build.

According to the site and the IBC, fireblocking, which would still be required, would be satisfied by the mineral wool which I already have in place. So the caulk I've been discussing may only be needed if I was attempting to create a draftstop. I'm going to look more into this, but caulk may not be needed at all if I'm only attempting a fireblock and not a draftstop.

[Quint]

What is the optimal density that should be achieved when mineral wool is compressed, to fit into a gap for creating a fireblock, so that it doesn't create any flanking between the inner and outer leaves of a room inside a room assembly?

For example, if I have a 1" gap and I'm placing 1.25" thick, 6 pcf mineral wool into this gap, that will result in a 7.5 pcf density once the mineral wool is compressed to fit into the 1" gap.

Is 7.5 pcf too dense where it will create flanking? What is the recommended final density that should be achieved? I've tried stuffing 1.25" mineral wool into the existing 1" gap I have.

I am able to tap on one leaf and slightly feel the vibration on the other leaf, so I'm concerned that the mineral wool is compressed too tightly in the gap, as it seems to be creating flanking. Or is a slight amount of flanking, as I described, to be expected when creating a fireblock and there's really nothing you can do to get rid of ALL flanking when creating a fireblock?

With 6 pcf mineral wool, how much larger than the gap should I be cutting it? Is 1.25" too much for a 1" gap? Maybe I should be cutting the mineral wool to be 1.125"? Should I be using a less dense mineral wool like 4 pcf?

The pictures (found them on the AVS forum and here) I've added to this post depict 4 pcf mineral wool and Thermafiber compressed to 25% (roughly 0.5"). After compression, the resultant density would be 16 pcf, which is double the density I'm achieving with my mineral wool. Can you really compress it that much and not create flanking at the fireblock?

[Gregwor]

The only other stuff that I can find (it's similar in price to GG... maybe a dollar a tube more expensive is the LePage PL Acousti-Seal
Here is the link to their page on it:
http://www.lepage.ca/en/lepage-products ... alant.html

After personally having a nightmare with this stuff 14 years ago, my friend experiencing the same thing, I looked into it more and actually found a thread on the forum where this crap ruined someones studio. Don't use it.

Greg