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What is this firewall sealant? How do I remove it? (Replacing Firewall)

Master Designs

Well Known Member
I'm removing and replacing my lower firewall in order to have easy access to replace my lower weldments in my RV-4, and the upper and lower firewall have been attached to each other with a firewall sealant before they were riveted together (sealant has been applied under the entire folded-over lip, the entire length of the FW). I was only going to replace the lower firewall, but the sealant the original builder used has become quite firm over the years, and I'm questioning how and if I can cut them apart. My plan would be to use a blade and slice the sealant; however, the recessed rivet holes will prevent the blade's travel.

Any suggestions? Or should I just replace both the upper and lower FW together while I'm at it?

Anyone know what kind of sealant this is? Color is a dirty chocolate color.

Thanks in advance for the help. :)

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firewall sealant?

Don't have an answer for your questions but that sure looks like tank Pro-Seal or another tank sealant!
 
sealant

Looks like proseal. If you want to remove without messing up the metal make a scraper from a piece micarta or plastic.
 
Sealant Remover

Polygone sealant remover gel from Van's: part is POLYGONE 300AG

Works well. Softens sealant. Use plastic scrapers as described above.

Best,
Mike
 
Problem is the sealant I need to remove/separate is what is hidden inside the entire length of the overlapping flange. I don't believe PolyGone, MEK, etc... will be able to attack the sealant inside? :eek:
 
If it's rock-hard, it might be automotive muffler sealant (silica-based... hardened). You might have to use a small die-grinder/cutoff wheel to slice thru the lower firewall section, and then use needlenose pliers to roll/remove the remaining strip off after all the rivets are drilled out.

BTW, a buddy of mine replaced his RV-4 lower motor mount weldments for replacement, without having to do any surgery on the lower firewall. It was a pain, and he used some 100 degree flathead/flushmount screws instead of rivets in some places that were impossible to get a bucking bar and rivet gun at. The screws had a hex/allen socket in the threaded end, and the "head" looked just like a flush rivet with smooth head. An allen wrench is used on them to hold it while tightening the nut.
 
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If it's rock-hard, it might be automotive muffler sealant (silica-based... hardened). You might have to use a small die-grinder/cutoff wheel to slice thru the lower firewall section, and then use needlenose pliers to roll/remove the remaining strip off after all the rivets are drilled out.

BTW, a buddy of mine replaced his RV-4 lower motor mount weldments for replacement, without having to do any surgery on the lower firewall. It was a pain, and he used some 100 degree flathead/flushmount screws instead of rivets in some places that were impossible to get a bucking bar and rivet gun at. The screws had a hex/allen socket in the threaded end, and the "head" looked just like a flush rivet with smooth head. An allen wrench is used on them to hold it while tightening the nut.

Those are called Hi-Lok fasteners, and they're great (but pricey). I used them on the canopy and rear window in my -7A tip-up to achieve the look of "rivets" on the entire exterior of the fuse and tip-up frame.
 
Neal- I have some slight tearing in the lower corners of the lower FW, so I want to replace the lower FW for sure. I'll look tomorrow morning when I get to the hangar about your cutting and peeling method. That just might work; although, I'd like to keep the FW intact so I can transfer the holes accurately.

Flying Scotsman - There are some Hi-Lok fasteners in the upper FW. I wondered what they were, and how to hold them while tightening the nut (haven't seen the backside to well since I don't have the FW off). Super cool fasteners. I'll take some photos tomorrow. Didn't know they were pricey; however, figuring the builder of my RV-4 worked at 'Skunk Works', it doesn't surprise me he had full access to all the cool stuff. :eek:
 
Neal- I have some slight tearing in the lower corners of the lower FW, so I want to replace the lower FW for sure. I'll look tomorrow morning when I get to the hangar about your cutting and peeling method. That just might work; although, I'd like to keep the FW intact so I can transfer the holes accurately.

Flying Scotsman - There are some Hi-Lok fasteners in the upper FW. I wondered what they were, and how to hold them while tightening the nut (haven't seen the backside to well since I don't have the FW off). Super cool fasteners. I'll take some photos tomorrow. Didn't know they were pricey; however, figuring the builder of my RV-4 worked at 'Skunk Works', it doesn't surprise me he had full access to all the cool stuff. :eek:

LOL! Let's just say he better not have :) We're not even allowed to take *scrap metal* from the bins for personal use...unless we want to get fired and face potential federal charges HA HA!
 
LOL! Let's just say he better not have :) We're not even allowed to take *scrap metal* from the bins for personal use...unless we want to get fired and face potential federal charges HA HA!

I was just kidding. Unfortunately, I never got to meet him as he passed away about 2 years ago....he was 93. I can tell you from his construction, he was one HECK of a good builder.
 
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I was just kidding. Unfortunately, I never got to meet him as he passed away about 2 years ago....he was 93. I can tell you from his construction, he was one HECK of a good builder.

I know...just kidding back at ya :). Glad you got yourself a nice plane to enjoy!

Genuine Aircraft Hardware has those Hi-Loks, by the way...do yourself a favor and by some really good ball-hex drivers to use with them. The cheap ones will kill your fingers trying to hold them and you'll worry that they'll snap at any time because the hex socket is pretty small. Ask me how I know this (no, the driver didn't break, but it was nerve-wracking watching it twist...).
 
That looks like Biotherm 100 firewall sealant, same stuff I used. I have no idea how to soften it up to remove but you can check the MFG website for ideas.
 
If you can get a blade in the joint between the rivets, you might be able to use piano wire (or thin guitar string, or even dental floss) to cut the sealant much closer to the dimple.

FWIW,

Charlie
 
another possibility ...

That might also be the "Hi-torque" RTV ... it's gray in color just like what's shown - gets much harder than regular RTV and is tough as all-get-out.
 
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