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Sealing the firewall

lostpilot28

lostpilot28

Well Known Member
Quick question for those that have done this before...I need to seal my firewall to remove the possibility of CO getting into the cabin. I bought some 3M fire stop caulk earlier today and was going to squeeze it along the seam inside the cabin, but I started wondering if this was the right thing to do.

Should I just put the caulk in the areas along the upper end of the firewall (along the top skin) that have the large relief grooves in it? Or should I put a solid bead around the entire firewall? Any suggestions are greatly appreciated.
 
around entire firewall

Your going to want to coat the whole thing, at least that is what I did. Also, I am building an 8A and I don't know how different they are around the cooling ramp area, but that requires sealent too. I used hi-temp rtv, as that was what I had at the time. I almost used household hi-temp stove caulking but I got to reading and it wasn't resistant to oil, something that is pretty important for that area. Good luck

Randy
8A wiring and finishing
hanging the engine today
 
Most firestop caulk is intumescent. It expands and chars, and forms a "pillow" of insulation when exposed to fire. Note that it works when exposed to the fire, so you use it on the engine side of the firewall.

In addition, anything you adhere to the occupant side of the firewall will result in smoke and fumes in the cockpit.

3M silicone base Fire Barrier 2000+ seems to be the choice. A lot of the 3M firestop stuff in the big box stores isn't even waterproof.

The initial (and possibly most important) sealing task is closing of these "holes' at the base of the flange tabs. This photo taken prior to installation of an insulation package and cowl flanges, so there is more sealant to be added later.

Do not use any kind of polysulfide sealant, i.e. proseal.
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I used red high-temp RTV between the fuselage skins and the firewall flange. I'm not sure what putting a bead on the inside would do for you if you've already done the flanges. Also, it is actually pretty tough to get at some of the firewall seams from the inside, given all the brackets and angle stiffeners.
 
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Thanks guys...

Dan, you make a good point about it being on the engine side of the firewall, but I was thinking that it was mostly just to block fumes. I'm not sure how I would get the sealant along the flanges on the engine side...doesn't seem easy to do if it's already riveted together.

Steve, I've noticed that the angle brackets are definitely in the way...any suggestions on how to seal the firewall after it's riveted together? The benefit of blocking fumes is obvious, just not sure how many people do it...especially with the quickbuild.
 
What about behind the brake reservoir?

How do you plug that hole behind the brake reservoir? It's the one that allows the brake line into the cockpit.
 
Dhall

Not sure about the heat vent - I don't see any easy way to seal this, but if there is air coming from the baffles, there should be positive pressure and that would tend to keep any engine-related CO out of the cabin.

Kelly,
For the brake line hole, I cut myself a large aluminum washer and put it on the firewall side of the hole, put red RTV on the back of the washer as well as in the center hole and that looks like it should take care of any leaks.

greg
 
lostpilot28 said:
Dan, you make a good point about it being on the engine side of the firewall, but I was thinking that it was mostly just to block fumes. I'm not sure how I would get the sealant along the flanges on the engine side...doesn't seem easy to do if it's already riveted together.
Click to expand...

In the above photo (EDIT, now lost) I had already riveted flange strips for 1/4 turn cowl fasteners, so the firewall tabs are the center of the sandwich. Didn't have any concern for the fay surfaces between the firewall tabs and the skin. I was interested in blocking the relief slots between the individual firewall flange tabs, as the inner end of each slot results in a series of "holes" around the firewall perimeter. Caulking the space between the trailing edge of the fastener strip and the firewall radius took care of it.

A caulk bead on the inside is probably the only way to completely seal both the fay surfaces and the slots on a QB fuselage. It would certainly be fine for fumes under normal conditions. It may or may not unseal when the firewall is subjected to fire, the question being "will the sealant remain adhered to hot stainless?". Second question is 'will it make smoke?"

Now I'm curious, so I just came from the shop. As it happens, I have a small firewall test burn rig. I've run a bead of Fire Barrier 2000 on both the front and the back of the stainless panel. Hang loose a few days. The heck with theory; let's see what the stuff really does.

EDIT See this thread: https://vansairforce.net/community/showthread.php?t=72087
 
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<< It may or may not unseal when the firewall is subjected to fire, the question being "will the sealant remain adhered to hot stainless?". Second question is 'will it make smoke?">>

The answer to both questions seems to be "no".

Subject material is 3M Fire Barrier 2000+, the silicone base intumescent caulk. I applied a bead to both the front and back of the stainless "firewall" panel on my little burn rig. The rig is calibrated to roughly 2000F degrees, so results may be a little different for the hot side at lower temperatures.





These were taken about 60 seconds into the burn.

On the "engine" side, the sealant did pretty much as expected; it swelled up and ablated. Didn't notice any charring. As the silicone binder burned away, the solids tended to be blasted off the surface by the flame jet. At the 60 second point most of it was gone.

The surprise was the "cockpit" side. When I flipped the burner to high, the entire sealant strip released and fell off the stainless surface before I could even get around the backside to observe. This was well before the firewall panel glowed red. You can see it in the above photo, and here is the undamaged strip:



The ablated material from the hot side easily crumbles to powder.



Ok, there is nothing very "scientific" about this check. I didn't make any effort to tightly control the test conditions, in particular surface preparation. However, I think we can make a few valid observations.

1. Hot side performance (ablation) was tested at or above the maximum manufacturer's spec under dsirect flame (after all, they do call it Fire Barrier 2000). It may work better at lower temperature levels or with a thicker bead. I'd suggest the best application would be one with mechanical shielding of the sealant, like standard firewall pass-through shields or a washer.

2. The ability of this sealant to adhere to clean stainless is questionable when heated. This check suggests that in the event of fire, it will release and do nothing if applied as a bead on the back side of the firewall.

3. I observed no significant smoke.

4. Probably a fine sealant to keep ordinary fumes and CO out of the cockpit under normal conditions. There may be better choices if you consider things like oil resistance; not a subject here.
 
3m fire barrier 2000+ corrosive to steel?

Dan-
When you were doing your research, did you come across any research that suggested 3M Fire Barrier 2000+ is pretty corrosive to steel.

Like this one from a Lancair builder (about halfway down the page):
http://www.aero-farm.com/ubbthreads/showflat.php?Cat=0&Number=230307&page=0&fpart=11&vc=1

Still trying to decide what to use on the firewall under my stainless steel grommet shields that I've used for my engine control cables.

Steve

DanH said:
<< It may or may not unseal when the firewall is subjected to fire, the question being "will the sealant remain adhered to hot stainless?". Second question is 'will it make smoke?">>

The answer to both questions seems to be "no".

Subject material is 3M Fire Barrier 2000+, the silicone base intumescent caulk. I applied a bead to both the front and back of the stainless "firewall" panel on my little burn rig. The rig is calibrated to roughly 2000F degrees, so results may be a little different for the hot side at lower temperatures.





These were taken about 60 seconds into the burn.

On the "engine" side, the sealant did pretty much as expected; it swelled up and ablated. Didn't notice any charring. As the silicone binder burned away, the solids tended to be blasted off the surface by the flame jet. At the 60 second point most of it was gone.

The surprise was the "cockpit" side. When I flipped the burner to high, the entire sealant strip released and fell off the stainless surface before I could even get around the backside to observe. This was well before the firewall panel glowed red. You can see it in the above photo, and here is the undamaged strip:



The ablated material from the hot side easily crumbles to powder.



Ok, there is nothing very "scientific" about this check. I didn't make any effort to tightly control the test conditions, in particular surface preparation. However, I think we can make a few valid observations.

1. Hot side performance (ablation) was tested at or above the maximum manufacturer's spec under dsirect flame (after all, they do call it Fire Barrier 2000). It may work better at lower temperature levels or with a thicker bead. I'd suggest the best application would be one with mechanical shielding of the sealant, like standard firewall pass-through shields or a washer.

2. The ability of this sealant to adhere to clean stainless is questionable when heated. This check suggests that in the event of fire, it will release and do nothing if applied as a bead on the back side of the firewall.

3. I observed no significant smoke.

4. Probably a fine sealant to keep ordinary fumes and CO out of the cockpit under normal conditions. There may be better choices if you consider things like oil resistance; not a subject here.
Click to expand...
 
Sealing The Firewall

My DAR told me to put my wife inside the cockpit, in the dark, with a bright flashlight and have her shine it around my firewall from the inside while I was outside.

Guess what I found... some light here and there, for a re-sealing.

And a CO2 dot purchase.
 
Took a few moments today to call 3M. Actually two calls, one to the technical call center and the other to a field rep for firestop products. Both gentlemen said corrosion of metals is very unlikely, as FireBarrier 2000+ is specifically designed to seal openings around metal pipe, conduit and sheet. It is a "certified" product, subject to a heap of construction standards and approvals.

The field rep said the "don't apply to painted surfaces" note is an adhesion caution.

Sorry, can't do any more for you....I'm no chemist.
 
Silicone and paint don't mix right?

I was sealing the firewall this evening and putting that 3M caulk between the skin and the firewall flange. I could see the caulk through the rivet hole and then I remembered that you shouldn't get silicone near any surface that you eventually want to paint. I guess the paint doesn't like to stick to it and it's impossible to clean off. I'm not using an excessive amount and haven't gotton any on the skin so I think I'm OK so far but are there any opinons out there about this? Should I just bag this idea and just shimmy up under the panel and try to put a fillet on the inside?
 
DanH said:
In the above photo I had already riveted flange strips for 1/4 turn cowl fasteners, so the firewall tabs are the center of the sandwich. Didn't have any concern for the fay surfaces between the firewall tabs and the skin. I was interested in blocking the relief slots between the individual firewall flange tabs, as the inner end of each slot results in a series of "holes" around the firewall perimeter. Caulking the space between the trailing edge of the fastener strip and the firewall radius took care of it.

A caulk bead on the inside is probably the only way to completely seal both the fay surfaces and the slots on a QB fuselage. It would certainly be fine for fumes under normal conditions. It may or may not unseal when the firewall is subjected to fire, the question being "will the sealant remain adhered to hot stainless?". Second question is 'will it make smoke?"

Now I'm curious, so I just came from the shop. As it happens, I have a small firewall test burn rig. I've run a bead of Fire Barrier 2000 on both the front and the back of the stainless panel. Hang loose a few days. The heck with theory; let's see what the stuff really does.
Click to expand...

Dan
I couldn't see the photo you refer to in this post. Could you put it up again?
 
Silicone and Paint

Silicone is the absolute enemy in the paint booth. However, there are prep solutions for degreasing and silicone removal.


ArVeeNiner said:
I was sealing the firewall this evening and putting that 3M caulk between the skin and the firewall flange. I could see the caulk through the rivet hole and then I remembered that you shouldn't get silicone near any surface that you eventually want to paint. I guess the paint doesn't like to stick to it and it's impossible to clean off. I'm not using an excessive amount and haven't gotton any on the skin so I think I'm OK so far but are there any opinons out there about this? Should I just bag this idea and just shimmy up under the panel and try to put a fillet on the inside?
Click to expand...
 
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