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Firewall Sealant Question

Lefty37

Member
Hi All,

I'm close to sealing the firewall on my fuselage and am looking for good suggestions for a firewall sealant. I've been considering a few options:
- Proseal (As recommended by Vans)
- Flamemaster CS-1900 (Mil-S-38249)
- PPG P/S-700 (Mil-S-38249)

I had intended to use 3m Firebarrier 2000+ but that is on backorder for a significant amount of time. I've been doing a fair amount of research on the site about this question, but a majority of the leads are from a long time ago. Any suggestions?
 
Based on recent tests, do not use proseal in any firewall seam.

Have not tested CS-1900 in a seam. Did ok as a cover for a grommet in an old test. Some flame, so don't leave any exposed on the cabin side of a firewall.

The PPG PS700 tech sheet looks very good, but $320 per pint? *&+#@!

I had hoped to test TA Aerospace 100-Series sealant, but I've had zero response from the company, and have not found anyone who claims to stock it.

Previously ran a sample of Cotronics Resbond 907GF, a ceramic type sealant. It is for all practical purposes, it is fireproof. The catch is that it sets rather hard. Need a burn test to see how it does between overlapped sheets.

Looking for other candidates, if anyone knows of something good.
 
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Hi Dan! Thanks for your response. I ran across your earlier tests, which greatly influenced my research. Looking at the safety required and level of protection available, I was trying (hard) not to flinch at the cost of protection in this case. Having not read anything about it, it would be interesting to see some tests of it. Or hear from people who've used it before. One question I did have was, how much sealant should I predict needing to seal the firewall? 6oz? 12 oz?
 
... how much sealant should I predict needing to seal the firewall? 6oz? 12 oz?

Can't say for sure, depends on waste. For a -7, you seal the edges of the recess box, the perimeter of the firewall, and any penetrations.

If you're committed to an aerospace sealant, buy the pint can. If you use less than half, it will resell quickly right here.

Take a hard look at the datasheet for PR-1995.

3M FireBarrier 2000+ is not designated as an aerospace product. It's a silicone based building construction firestop. I've stuck with it because (1) it does well in fire tests, and (2) it has held up very well in my own engine compartment, 12 years and 1100 hours. It's no small thing. For example, consider how unhappy an owner might if a particular sealant has poor long term resistance to engine oil.

With that in mind, does anyone have long term experience with 3M 3000WT. or Biotherm 100?
 
Based on recent tests, do not use proseal in any firewall seam.
SNIP

Shoot fire Dan, you are blowing another standard process for me. I’ve always used ProSeal on the firewall to side skin seams to prevent oil and such from migrating into the cabin - and it has worked well on three RVs.

So as a disciple of the Dan Horton firewall insulation process, I’ll soon need to know the replacement options for my trusty can of ProSeal. The fuselage is going together on the new RV-10.

Carl
 
question :- If sealing is required, why do quickbuild fuselages come with teh firewall to skin seam unsealed ?

The air vent flap/box is aluminium and more likely to melt before the firewall itself.

Just asking.....
 
question :- If sealing is required, why do quickbuild fuselages come with teh firewall to skin seam unsealed ?

The air vent flap/box is aluminium and more likely to melt before the firewall itself.

Just asking.....


Very good question if that's the case...


As for the air vent flap/box, best practice would suggest to use a stainless steel part.
This example for RV-7, -8, -9
https://www.aircraftspruce.com/catalog/eppages/heaterbypass2.php
 
Hmmm... the cabin hot air flap box that I got from Vans is aluminum. Is it junk? Replace it with the stainless version for another 0.2 AMU$? But then, the cowling is only epoxy, and the firewall side cheeks are of aluminum, so would it really solve a problem if there is actually a fire?
 
Hmmm... the cabin hot air flap box that I got from Vans is aluminum. Is it junk? Replace it with the stainless version for another 0.2 AMU$?

Entirely your choice. It does not protect against all fire risks. It does improve your chances.
 
Whats available to do a few grommets right now?

The classic approach for rubber grommets is a stainless steel shield. Example:

https://www.aircraftspruce.com/catalog/appages/firewallshields3.php?clickkey=190107

A tiny quantity of any high temperature, oil resistant silicone sealant (I like Permatex Ultra Black) on the engine side makes the assembly air tight. It's not needed if the grommet fits tight.

Plastic snap bushings really need an intumescent sealant, and even then they will melt in a short time. Current state of the art is way beyond snap bushings.
 
3 M fire barrier usually available in aviation dept of Home Depot

Caution, Will Robinson....

The home stores sell 3M "IC 15WB+ Fire Barrier" and 3M "CP 25WB+ Fire Barrier" caulks. These are latex products, not silicone, and are only rated for max service temperature of 180F. They are also far less durable. For example, the silicone sealant has three times the tensile strength and a rated elongation of 500% at break, both good things for a dynamic application like an airframe. Oil resistance of a latex is unknown.

I've also looked at Fire Barrier 1000NS and 3000WT, silicone based intumescent sealants. Neither appears to be a substitute for Fire Barrier 2000+, based on published properties.
 
Caution, Will Robinson....

The home stores sell 3M "IC 15WB+ Fire Barrier" and 3M "CP 25WB+ Fire Barrier" caulks. These are latex products, not silicone, and are only rated for max service temperature of 180F. They are also far less durable. For example, the silicone sealant has three times the tensile strength and a rated elongation of 500% at break, both good things for a dynamic application like an airframe. Oil resistance of a latex is unknown.

I've also looked at Fire Barrier 1000NS and 3000WT, silicone based intumescent sealants. Neither appears to be a substitute for Fire Barrier 2000+, based on published properties.

Good point on latex products. (I'll have to investigate that, as I personally wasn't aware of any latex based fire stop products.) I had silicone products in mind, which I have used in the past. Never for stopping an actual firewall fwd fire, but to seal various things up front on the plane and professionally for life safety code compliance. Clean and degreased surfaces are a must so the silicone based product can flex and remain bonded/sealed.
 
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Firewall protection

Entirely your choice. It does not protect against all fire risks. It does improve your chances.

I've had a closer look at the Vans aluminum hot air flapper valve box and I think it will be relatively easy to make it more robust in case of fire by replacing some of the aluminum components with stainless. I have some stainless sheet and stainless piano hinge and will replace the flapper part and also add a stainless backing plate inside the box where it contacts the firewall. If this is done then then the rest of the box could melt and fall off and there will still be a stainless section left to cover the 2 inch hole in the firewall. The bowden control wire is on the aft side of the firewall so it should be OK as is.

The separate and subseqent comment in the thread about the Vans recommended method of using snap bushings and sealant for cable pass throughs would indicate that some of us are overly sensitive about the risk of engine bay fires, or that Vans believe that their methods are adequate. It is hard to decide what applies in the absence of data. It would be interesting to know what losses have occurred due to the use of snap bushings in the firewall.
 
I've had a closer look at the Vans aluminum hot air flapper valve box and I think it will be relatively easy to make it more robust in case of fire by replacing some of the aluminum components with stainless.

Aircraft Spruce has a pretty nice cabin heat box that is all Stainless Steel and has the operating control arm on the cockpit side for around $100.
 
Aircraft Spruce has a pretty nice cabin heat box that is all Stainless Steel and has the operating control arm on the cockpit side for around $100.

Thanks I saw that, for me shipping via UPS is approx minimum $50 and with the current reduced exchange rate of $0.60 USD per $1.00 AUD that makes it $250. In daily living terms that's another chunk and I already have the flapper box that Vans sent, so really just trying to make the budget work and avoid death by a thousand cuts!
 
It is hard to decide what applies in the absence of data. It would be interesting to know what losses have occurred due to the use of snap bushings in the firewall.

There is no data to address the question. I doubt there ever will be. NTSB reports focus on the primary cause, and rarely go into any depth about subsequent failures.

Here's a good example. The investigators did a marvelous job of tracing the primary cause (an engine failure) back to a strainer screen which had not been serviced.

https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/101427/pdf

However, an engine failure is not necessarily fatal, in particular over the wide open fields of Dallas County, Alabama. The occupants died because they lost control of the airplane and dug a deep hole.

The limited discussion of fire in the cockpit is found on the second page...

....Insulation located underneath the glareshield exhibited thermal damage. In addition, wiring located behind the instrument panel was thermally damaged.

So, the fire transferred from the engine compartment to the cabin, but there is no attempt to identify how or why.

It's left to us to learn what might have contributed, and avoid building those things into our airplanes. Think of it as the "first do no harm" rule, i.e. don't install stuff with the potential to increase fire risk. (Potential Darwin award winner pictured below; aluminized plastic bubble wrap on a firewall.)

From there, it's about increasing time before loss of control. With a good sealant, plastic snap bushings will melt in less than a minute in direct flame, less than two with mostly conductive heating. The subsequent open hole may or may not contribute to a chain; depends on what is installed behind the firewall. Steel ball or tubular penetrations will last much longer.

We get to pick our level of fire resistance, and we get to do our own maintenance too. It's a lot better than the cards dealt to the guys in the Lance.
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I wondered about that accident in the Lance and whether the pilots could have done anything differently and survived, even though the root cause was no fault of theirs.

The attached pics are of the passthrough shields that I have. It is going to take some creativity and modification to get them to fit in the recommended locations on the FWF plans for the RV-7 firewall.

Just for interest I heated some stainless and aluminium sheet with the same flame and the aluminium shmelted well before it got red. I'm not sure how the rubber grommets that go in the stainless shields will fare, I suspect they will give off acrid fumes. The aft side of my firewall is bare stainless. The third pic (sorry it's rotated 90 degrees counter-clockwise) shows the right edge of the firewall that is built to plans. In the early kits the cheeks are aluminum and not stainless and will presumably be another weak point in case of an intense fire. I have yet to seal the seams.
 

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