Interior firewall insulation replacement

[Matthew P]

The old cloth covered interior firewall insulation is completely deteriorated and needs to be pulled out and discarded in my 1965 M20E. 

What do you all use in its place as a thermal barrier?

 

V/r

 

Matt

[N201MKTurbo]

38 minutes ago, Matthew P said:

The old cloth covered interior firewall insulation is completely deteriorated and needs to be pulled out and discarded in my 1965 M20E. 

What do you all use in its place as a thermal barrier?

 

V/r

 

Matt

I have thought about doing that a few times. To do it properly requires removing the firewall. This would be a major undertaking. You would need to remove the engine and then drill out all the rivets holding the firewall in place. Then deal with all the stuff that goes through the firewall.

[Matthew P]

I was thinking just what's accessible on the backside of the firewall in the foortwells, I have all that hanging cheesecloth type material that's tied off in places to keep it up off the floor...at this point it serves no purpose and as worn as it is I'd be concerned that a spark would be enough to get a fire going.

[jamesm]

I have done many years ago  when I had the engine overhauled  it silver flame resistance material it met part 25 requirements and burn papers that came with it.

The finish component looked ok (wasn't that great),  fast forward say 12 years or so,  let just say my feet have no grace so the top foot well on the cabin side looks like hell now.  When the firewall still  on  the plane there is no way to feed the insulation material under truss and structure of the airframe, it can't really be done at least if there is a way I couldn't tell you. Like Rich said to do right, you  would have to completely disassemble the firewall.  which to me looks like no easy task.

James '67C

[M20F-1968]

I did this then in rebuilt the airframe.  I made a firewall blanket from soundproofing material.  It was installed after the firewall was in stalled but before the avionics were installed , as I remember.  I would need to check my old pictures of the project to verify.  However, you need to deal with what you have.  

You can make a firewall blanket and slide it between the firewall and the avionics and wires.  The old firewall sound-proofing must be removed.  It can be installed with threaded fasteners (machine screws) appropriate for high temperature installation.  You will not need many fasteners.  The firewall blanket can be made in sections so it is easier to install, but I can assure you it will be a PITA to install.   You might find a young, small, flexible, and willing assistant to help.

As you already know, working behind the panel in a Mooney is always challenging.  It's the price you pay for a small frontal area and speed.

John Breda

[N201MKTurbo]

I believe the original firewall blanket is a bit more high tech than most realize. I think the fabric is some kind of high temperature fabric like aramid or mineral fiber. and the material behind it is fiberglass. This can withstand a raging fire in the engine compartment and keep the heat away from you. As far as its flammability is concerned, it was not flammable when it came from the factory, but after decades of absorbing lubricants sprayed behind the panel, all bets are off.

[DXB]

BUMPING THIS HIGHLY RELEVANT THREAD.    While doing a thorough cleaning of my M20C interior over the weekend, I noted the decrepit condition of my 57 year old firewall blanket on the cockpit side:  multiple holes, decrepit fiberglass shards leaking out from them.  As @N201MKTurbo notes, this looks like a massive job to do properly.  Has anyone come up with a satisfactory stopgap solution?

[MikeOH]

I hate to bring this up...but any chance the old material contains asbestos?  If so, I'd be very careful, and wear a VERY good respirator, when removing it.

[cliffy]

Maybe call a very good interior shop and ask how they do it OR better yet - Do They?

I'll bet the original was fiberglass covered in some kind of fabric.

I think it is only for heat protection during normal flight (passenger comfort) as the steel firewall meets the time requirement for flame proofing in case of an engine fire. 

Boeing uses a foil covered "fiber" inside their fuselages that I'd bet would work but would it be certifiable?

Some IAs might baulk at using anything not certifiable 
 

[DXB]

2 hours ago, MikeOH said:

I hate to bring this up...but any chance the old material contains asbestos?  If so, I'd be very careful, and wear a VERY good respirator, when removing it.

I was afraid to bring up the same question....but does anyone know? It is spontaneously fragmenting through gaps in the fabric that encases it.  I may already be screwed after my recent unprotected clean up of bits of it lying around in the foot wells.  It's a very nicely updated plane otherwise - I'll leave it in my will to a Mooniac TBD who has appropriate hazmat skills.  

[MikeOH]

9 minutes ago, DXB said:

I was afraid to bring up the same question....but does anyone know? It is spontaneously fragmenting through gaps in the fabric that encases it.  I may already be screwed after my recent unprotected clean up of bits of it lying around in the foot wells.  It's a very nicely updated plane otherwise - I'll leave it in my will to a Mooniac TBD who has appropriate hazmat skills.  

If have some material you can buy a test kit at Home Depot and send it to a lab to find out (IF you want to know)

https://www.homedepot.com/p/PRO-LAB-Asbestos-Test-Kit-AS108/202731785

 

[DXB]

On 5/5/2025 at 9:19 AM, N201MKTurbo said:

I believe the original firewall blanket is a bit more high tech than most realize. I think the fabric is some kind of high temperature fabric like aramid or mineral fiber. and the material behind it is fiberglass. This can withstand a raging fire in the engine compartment and keep the heat away from you. As far as its flammability is concerned, it was not flammable when it came from the factory, but after decades of absorbing lubricants sprayed behind the panel, all bets are off.

 

36 minutes ago, cliffy said:

Maybe call a very good interior shop and ask how they do it OR better yet - Do They?

I'll bet the original was fiberglass covered in some kind of fabric.

I think it is only for heat protection during normal flight (passenger comfort) as the steel firewall meets the time requirement for flame proofing in case of an engine fire. 

Boeing uses a foil covered "fiber" inside their fuselages that I'd bet would work but would it be certifiable?

Some IAs might baulk at using anything not certifiable 
 

It does indeed look like a very sturdy golden/amber fabric encasing fiberglass - just not sturdy enough, as it has come apart at the bottom of the foot wells behind the rudder pedals, and in a few spots above.  It seems like one should just fasten some more fabric over it in the areas that have just opened up.  I don't see any way to replace it fully without entirely dismantling the avionics, most all else behind the panel, and the panel itself.  Even then cleaning it out will be a messy job. I might even tackle the patch job myself if someone can tell me what fabric to use.  I want to avoid doing a sketch job with dissimilar materials so as not to inspire regulatory scrutiny (or premature demise in a fire). 

[DXB]

Thinking of using this black nomex fabric to cover over the ugly disintegrating areas - thoughts?? 

https://www.pegasusautoracing.com/productdetails.asp?RecID=3136

Maybe use a simple stitch gun to tack it in place over the old material??

https://www.amazon.com/MicroStitch-Tagging-Gun-Kit-Fasteners/dp/B001CE8JPQ?th=1

[DXB]

29 minutes ago, MikeOH said:

If have some material you can buy a test kit at Home Depot and send it to a lab to find out (IF you want to know)

https://www.homedepot.com/p/PRO-LAB-Asbestos-Test-Kit-AS108/202731785

 

I'm thinking of the ensuing pandemonium in the Vintage Mooney community that a positive result would bring, plus the airworthiness directive whose cost will total our planes

I'll hold off for now unless someone has real info that asbestos might have been used 

[N201MKTurbo]

It doesn’t look like asbestos to me. It looks more like Kevlar. The stuff behind is fiberglass.

[DXB]

4 minutes ago, N201MKTurbo said:

It doesn’t look like asbestos to me. It looks more like Kevlar. The stuff behind is fiberglass.

You're probably right - it looks pretty much like this.  Tacking this stuff with a stitch gun over the old materials in the foot wells shouldn't be too hard...

https://www.soundassured.com/products/fire-retardant-acoustic-fabric?variant=45293361397918&utm_campaign=gs-2021-06-21&utm_source=google&utm_medium=smart_campaign&gad_source=1&gad_campaignid=17518101047&gbraid=0AAAAADiZDVTaGw9_7gsEXMZ1EZygrZXWp&gclid=CjwKCAjwk7DFBhBAEiwAeYbJsTqyqokx5iicq23eDzEJTUH9uOOXqF1tZRB2MhmUO94pbxlgORVZFxoCDMUQAvD_BwE

[MikeOH]

12 minutes ago, N201MKTurbo said:

It doesn’t look like asbestos to me. It looks more like Kevlar. The stuff behind is fiberglass.

Hmm, Kevlar was invented in 1965...57 year old M20C, ya think Mooney was that early an adopter?

[N201MKTurbo]

1 hour ago, MikeOH said:

Hmm, Kevlar was invented in 1965...57 year old M20C, ya think Mooney was that early an adopter?

I don’t know. Somebody should ask Mooney.

[MikeOH]

Just now, N201MKTurbo said:

I don’t know. Somebody should ask Mooney.

LOL!

That makes way too much sense!

[N201MKTurbo]

1 hour ago, MikeOH said:

Hmm, Kevlar was invented in 1965...57 year old M20C, ya think Mooney was that early an adopter?

More likely to be Nomex. It was commercialized about 10 years earlier. 

[MikeOH]

7 hours ago, N201MKTurbo said:

More likely to be Nomex. It was commercialized about 10 years earlier. 

Could be.  Maybe Mooney knows?

[cliffy]

In reality asbestos is a problem but not an instantaneous death kneel. 

Asbestosis killed many who worked in factories for years that used asbestos in manufacture (old brake shoes).

It took years of exposure for it to be a real problem Just one exposure or even a series of short exposures probably won't cause much of an impact. Its not instantly "poisonous".

Many of us "older" folks were near it occasionally (brake dust) with no impact on health. 

However those who came in contact on a regular basis had problems - Asbestosis

 

Asbestosis (as-bes-TOE-sis) is a chronic lung disease caused by inhaling asbestos fibers. Prolonged exposure to these fibers can cause lung tissue scarring and shortness of breath. Asbestosis symptoms can range from mild to severe, and usually don't appear until many years after initial exposure.

[Matthew P]

Posed the question to Frank at Mooney and his response was:

"Not sure, but probably looking at Material: MIL-B-5924B Type 1."

OR Owens-Corning PF334

[DXB]

26 minutes ago, cliffy said:

In reality asbestos is a problem but not an instantaneous death kneel. 

Asbestosis killed many who worked in factories for years that used asbestos in manufacture (old brake shoes).

It took years of exposure for it to be a real problem Just one exposure or even a series of short exposures probably won't cause much of an impact. Its not instantly "poisonous".

Many of us "older" folks were near it occasionally (brake dust) with no impact on health. 

However those who came in contact on a regular basis had problems - Asbestosis

 

Asbestosis (as-bes-TOE-sis) is a chronic lung disease caused by inhaling asbestos fibers. Prolonged exposure to these fibers can cause lung tissue scarring and shortness of breath. Asbestosis symptoms can range from mild to severe, and usually don't appear until many years after initial exposure.

I was joking about the immediate threat of death, but asbestos does have a unique and potent combination of cancer-causing properties. When it fragments, it generates fibers that have a critical combination of 3 features: (1) very sharp and stiff   (2) very fine and light, allowing them to float all the way to the outer lining of the lung (pleura) and impale themselves there.  (3) impossible for immune cells (macrophages) to digest or wall off at this location, leading to chronic immune activation and ultimately mesothelioma (cancer of the pleura).   Interestingly, fiberglass has features (1) and (3) but lacks feature (2) - the fibers are generally too heavy to float deep into the lung.  There is some link between fiberglass dust exposure and mesothelioma, but it is much, much weaker than for asbestos, probably for this reason.

You have to have a large, sustained (typically occupational) exposure to asbestos fibers to devlelop clinically evident asbestosis.  By contrast, even a few of these fibers in your lung can ultimately cause mesothelioma - hence even modest exposures are best avoided, and people rightly go apesh*t when asbestos needs to be handled in a way that causes it to fragment. 

[DXB]

58 minutes ago, Matthew P said:

Posed the question to Frank at Mooney and his response was:

"Not sure, but probably looking at Material: MIL-B-5924B Type 1."

OR Owens-Corning PF334

Various older forms of fiberglass it looks like, not asbestos.  The folks hoping for my demise can stop salivating now...