Sealing the firewall

lostpilot28 · #1 10-11-2008, 07:08 PM

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.

N208ET · #2 10-12-2008, 06:34 AM

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

DanH · #3 10-12-2008, 09:44 AM

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.

alpinelakespilot2000 · #4 10-12-2008, 09:46 AM

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.

lostpilot28 · #5 10-12-2008, 04:13 PM

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.

ArVeeNiner · #6 10-12-2008, 04:21 PM

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

dhall_polo · #7 10-12-2008, 05:54 PM

So... what is recommended around the cabin heat access?

Greg Arehart · #8 10-12-2008, 09:33 PM

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

DanH · #9 10-13-2008, 08:43 AM

Quote:

Originally Posted by lostpilot28

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.

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.

lostpilot28 · #10 10-13-2008, 10:30 AM

Excellent...thanks Dan. Looking forward to your findings.