Firewall sealant: 3M CP 25WB+

[Junglepilot]

I am converting a 8A to 8 and removed the forward skins and FW to replace with new -8 skins.

That said, as I began to look at the reinstall I saw the note about sealants for the FW to floor skin. In the removal I found the previous builders sealants.

So I began looking at the options. The CS1900 is one that pops up a lot and several others that are Big$$. Of course, then there is simple red high temp RTV.

Next I spoke with several builders, one DAR and even Van's tech people.

Bottom line in my decision is this: The primary purpose of the seal is to keep out fumes that can incapacitate the pilot, not for fire protection primarily. That's what the mixture lever is for.

• The problem I have with RTV is that silicone tends to draw moisture ( I flew in the Amazon rainforest for 8 years and saw that first hand). Also RTV can be somewhat corrosive to aluminum.

• The problem I have with the CS1900 is it is $60 for a tiny can. (product, hazmat fee, shipping)

Then I found an interesting product from 3m called 3M CP 25WB+.

It is an intumescent meaning it expands when heated thus increasing it's [vapor] seal in a fire and is a "light char" intumescent. That means it also retards heat transfer. Both good for what this seal is supposed to do. In addition one of the primary ingredients is ground up fiberglass.

Of course other products may do a great job and have as many good features no doubt. Not saying it's the best thing available.

However the best is this: it'll do the job, it is not under hazmat and it is only about $ 12.00 for a standard 10 oz. tube (i.e size to fit in caulking gun) and is available at Home Depot/big box stores. All good things and a safe compromise when working on a $$ project like an RV-8. One of my favorite quotes about saving money is from Ben Franklin: "Watch the pennies and the dollars will take care of themselves"

At the end of the day, I am comfortable using this product.

Anyway I thought my decision process might be helpful to someone else. Found more than one thread on this all with many conclusions and ideas.

[Bevan]

I can't comment on your suggestion although it sounds good. My question is this. My firewall has been installed but not yet riveted to the side/bottom skins. I don't recall and have to look but doesn't the fume-proofing material need to go all the way around the firewall, not just at the bottom? And if so, is this applied immediate prior to riveting in between the mating surfaces? If not, how else would you seal it? Cause you really can't get at the aft side to lay a bead of sealant where the corner welments are located.

Bevan

[Junglepilot]

For gasses, I am putting a bead along the bottom and sides and possibly the top prior to riveting. The main reason I think the bottom seal is important is because of the exhaust running immediately below that location and air pressure forcing escaped gasses through any openings.

The side seal would be more protection for upper deck leaks, even though the air flow should carry escaped gasses down and out. Hence the need for the bottom seal.

In a fire the sealant will swell along the bottom and sides offering a few seconds of protection (1) giving me time to pull the mixture and get the nose poked down (assuming I know there's a fire as engine fires in a single are hard for pilots to see) or (2) before the aluminum melts through and the engine departs.

[longranger]

Originally Posted by Junglepilot

...In a fire the sealant will swell along the bottom and sides offering a few seconds of protection (1) giving me time to pull the mixture and get the nose poked down (assuming I know there's a fire as engine fires in a single are hard for pilots to see) or (2) before the aluminum melts through and the engine departs.

Probably also want to shut off the fuel valve and make sure any pump(s) are off in case of a leak upstream of fuel injection or carb. That would come to my mind before pullng the mixture.

[Junglepilot]

Which brings to mind the need for everyone to have an emergency procedures checklist on a card in large type/easily legible that they can pull out in such emergencies.

Then practice it regularly and know it without having to refer to the card.

The card is for reference.

Thanks for the input!

[MikeT]

How about this stuff?

http://www.aircraftextras.com/Contego.htm