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Old 11-15-13, 10:39 AM   #1
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Default Fireblock foam burns

I know that spray foam is generally considered to be combustible even when cured but I figured that Dow Great Stuff™ Fireblock foam would be a little harder to ignite than it is.

I didn't put much thought to it and I've been using it since it is available and figured that most people that I've talked to and most online sites about conservation say to use spray foam and don't generally display a concern for fire safety in its use. I figured that this fireblock foam was a better option than the standard stuff, but after playing with it, I'm not sure I'll be paying the extra expense anymore.

I figured I'd need a torch to light the stuff but when I took it outside on the concrete front step, it took about two seconds of contact with the flame of a common butane lighter and it was lit and continued to burn unaided when the lighter was removed.

Here are the points that I figure that people are sold on:
Impedes spread of fire and smoke through service penetrations
Recognized as an Alternate Fireblocking material for residential construction
Tested according to ASTM E84, ASTM E814 (modified), UL 1715
Bright orange colored foam for easy code identification

The only understanding that I have is that the idea of preventing air movement could prevent flame spread.

Here is part of a statement from Dow in response to someone's online review of this product.
"GREAT STUFF (TM) Insulating Foam Sealant products should not be used around heaters, furnaces, fireplaces, or recessed lighting fixtures where it contacts heat conducting surfaces. Cured foam is combustible and may present a fire hazard if exposed to flame or temperatures above 240F."
and
"GREAT STUFF™ FireBlock Insulating Foam Sealant is a minimal-expanding, single-component foam sealant for general purpose building envelope air sealing. This product is defined by the International Building Codes as the use of approved building materials installed in concealed spaces to resist the migration of fire and hot gases. GREAT STUFF™ FireBlock is tinted orange to be more recognizable to building code officials. This product is not approved for use in firestop systems. The Dow Chemical Company makes the GREAT STUFF™ products, if you are looking for other material other than GREAT STUFF™, please refer to 3M’s website."

I added the bold above instead of just posting a partial quote the second statement to keep it in context.

My point is that this product is not an intumescent firestop like some spray foams or encapsulants for spray foams can be. The can does say "Residential Fireblock Penetration Sealant". It also has flame spread characteristics but I don't know what those numbers mean but figured they were numbers that indicated that it was not very flammable. I think that 'FireBlock' is a little bit deceiving as it seems very similar in name to firestop, which is something Dow says its not. Although when looking at the can it doesn't say that it isn't a firestop. The part that says "Flammable. Avoid sources of ignition, open flame, temps above 240f (116c). Pressurized. Can may burst. Do not punture or incinerate. Avoid temps above 120f (49c)." suggested to me that this was when applying the product due to the flammable nature of the propellants used in spray foam.

Why am I posting this thread?
I have seen others on this forum either mentioning its use(and at least one picture) to seal up the knockout penetrations for wires around junction boxes such as light switch boxes, electrical outlet boxes, and light fixture junction boxes. A junction box is designed to be a fire resistant container designed to contain most short circuit arcing(such as bad twist-on wire connections) and overloads until the circuit breaker or fuse blows. They are a specific size, thickness, and material to contain a certain amount of heat. It's my opinion that the knockouts should be sealed, especially when these are covered in insulation in an attic and that heat or arcing would otherwise contact the insulation along with the air sealing needs for conservation.

I personally use a fire rated caulking UL 1479 rated for filling the air gaps in the attic facing junction box knockouts. I think spray foam is just fine in places other than electrical junction boxes and combustion venting, since it is then behind drywall or other fire rated materials in the same area that other materials that burn are located such as wood framing for example. A UL 1479 fire-rated product similar to this is what I think is ideal for electrical junction box air sealing. DAP Fire Stop 10.1 oz. Silicone Sealants (2-Pack)-181244 at The Home Depot I actually used a White Lightning based UL 1479 product but I can't find the same product(their UL 1479 stuff) anymore.

Thoughts?


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Old 11-15-13, 10:53 AM   #2
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Good to know. I know I've used regular great stuff in my electrical boxes. While I don't foresee it being an issue, I will change what I use in the future. Thanks.
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Last edited by Daox; 11-15-13 at 11:29 AM..
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Old 11-15-13, 11:14 AM   #3
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Granted it doesn't light up and burn like paper but it is easier to start on fire than say holding a lighter to a 2x4, for example.

I found a couple of demonstrations of how it burns. My experience of using a lighter to this stuff was very similar to the DAP fireblock video.

DAP fireblock


Dow Great Stuff Pro Gaps and Cracks


Comparison of one firestop foam and two fireblock foams

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Old 11-15-13, 11:37 AM   #4
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Here's another nice video, it goes into some detail with informal torch application to a number of different insulation materials including multiple forms of batt insulation, cellulose, aircrete and foams.
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Old 11-15-13, 09:56 PM   #5
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Thanks for posting! Fortunately for me, I had access to a commercial firestop product when I needed it while I was building. Very interesting that the closed cell insulation seemed to perform better than the greatstuff "firestop".
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Old 11-15-13, 11:02 PM   #6
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Wow! Thanks for the information.
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Old 11-15-13, 11:24 PM   #7
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I prefer using drywall mud in the cheese whiz container, whatever it's called. Inherently cheap, not gonna burn. Seals up like real mud.
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Old 11-16-13, 08:46 AM   #8
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You could use duct mastic to seal the holes. Would be interesting to see a burn test done on it since it's used on furnaces.
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Old 11-16-13, 11:27 AM   #9
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I understand that duct mastic is used on ductwork but is it also used on the critically hot areas such as exhaust flues? I'd figure a masonry fireplace sealant would be okay too. It might be a good idea to check the conductivity(in case it flows into the box a little) and adhesion to the surfaces you want to have it attach to as well. I think its still a better idea to stick with something that is rated for both UL 1479 and UL 2079 when in an area that has an increased hazard. Granted a 4 hour fire rating with a product like this might be a little overkill but it's only $11.47 and the tube could handle all of the more hazardous air sealing for most houses. Shop 3M 10.1-oz Red Specialty Caulk at Lowes.com
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Old 11-16-13, 03:28 PM   #10
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I'm not aware of ordinary duct mastic able to handle the high heat on furnace exhaust piping.

I'd go with what MN Renovator suggested RE: masonry fireplace sealant instead (or any proper UL rated/fire rated sealant).

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