Corrosion Behind Foam Replacement Insulation

[AerostarDriver]

In rectifying some of the few deferred maintenance items on my 71 M20E, I elected to remove the foam that had been installed to replace the fiberglass as part of the guidance in SB208. However, the foam installed in my airplane was not the Mooney kit but rather a black/gray self stick foam. While, I had not though to grab pictures of the foam before I removed it, the foam looks extremely similar to the foam featured in Mark Gunnison's youtube video (I believe I have dropped it in with the correct time). Upon removing this foam I found that it has reacted with the existing green primer (Unknown if it is original), wherever the foam was attached the primer has cracked and flaked off creating some minor general surface corrosion with some deeper pockets of pitting on the aluminum surfaces. The panel worse effected where the baggage compartment bulkhead, which was peculiar to me as their is limited ways for water to find its way to that panel.

Working with my A&P we have a solution which evolves removing the effected primer, using scotchbrite to clean up and remove the corrosion and then etch prime all effected areas. Has anyone else experienced this? Has anyone ever looked behind the self stick foam? I already have the Mooney SB M20-208B foam kit but is their any reason to look at other options?

I know I am posting this without pictures but left my camera at the airport. Should have pictures by Thursday.

[PeteMc]

The pitting is what I'd be concerned about.   Is the structural integrity compromised?  (aka strength of the tube)

[AerostarDriver]

4 minutes ago, PeteMc said:

The pitting is what I'd be concerned about.   Is the structural integrity compromised?  (aka strength of the tube)

I may have not been clear in my post, all corrosion is on the ALUMNIUM skins and baggage compartment bulkhead, behind the foam panels.

My SB 208 inspection was near prefect. The decision to replace the foam was due to the fact that some how I ended up with a 208B foam kit and finding out the foam was not the same we elected to "make it right". We would have never known about the corrosion on the ALUMNIUM if we did not remove the foam.

Edited February 3, 2021 by AerostarDriver

[hammdo]

Clean the skin, apply CorrosionX to it should be ok. Good on you to replace the insulation...

-Don

[carusoam]

AD,

Is there a reason you didn’t take a pic to share what you are discussing?

We’re you able to find in your logs what the foam is that was installed?

For explanations of how water gets into so many places in an airplane...

Air carries water, temperature changes allow condensation to occur...

Condensation can occur on any surface in the plane... and run with gravity...

 

Post some pics if you have them...

Best regards,

-a-

[AerostarDriver]

1 minute ago, carusoam said:

AD,

Is there a reason you didn’t take a pic to share what you are discussing?

We’re you able to find in your logs what the foam is that was installed?

For explanations of how water gets into so many places in an airplane...

Air carries water, temperature changes allow condensation to occur...

Condensation can occur on any surface in the plane... and run with gravity...

 

Post some pics if you have them...

Best regards,

-a-

I need to run back to the airport to grab my camera. I don't have pictures of the old foam installed but I have pictures of the damage. I still have the foam that was removed and can get a picture of it as well. The issue I have has more to do with the rapid degradation of the protective zinc chromate layer. You can see where the foam was because it has spiderwebbed the primer layer in the exact places where the foam was located.

As far as log books go, I have a few entries from the late 2000s which indicate SB M20-208B was complied with but beyond 1993 I can't make any determination as all the logbooks are in Japanese. If I where to guess it was likely installed in 2009 when a long list of other mods where installed by a new owner. That owner also had a pretty good A&P who had a separate entry for every non annual item. If that is the case, the foam would have only been installed for 10 years.

 

[carusoam]

Pics of the aluminum you are trying to stabilize Would be good...

We have many mechanics around here that can put an eye on the pics...

And give insight...

Some parts can appear to be structural... and not be...

Others look like they are part of a bench... and turn out to be structural...

Some corrosion is surface type... easily cleaned and properly painted...

 

As far as translating logs go... we know of one Mooney pilot in Japan... 

Pp thoughts only, not a mechanic...

Best regards,

-a-

[AerostarDriver]

17 minutes ago, carusoam said:

Pics of the aluminum you are trying to stabilize Would be good...

We have many mechanics around here that can put an eye on the pics...

And give insight...

Some parts can appear to be structural... and not be...

Others look like they are part of a bench... and turn out to be structural...

Some corrosion is surface type... easily cleaned and properly painted...

 

As far as translating logs go... we know of one Mooney pilot in Japan... 

Pp thoughts only, not a mechanic...

Best regards,

-a-

I will have pictures posted Thursday.

Help translating what I have would be excellent. Some I can read though the lines, other parts are a complete mystery.  

[hammdo]

Where’s google translate ;o)

-Don

[AerostarDriver]

5 hours ago, hammdo said:

Where’s google translate ;o)

-Don

From factory delivery in March of 1971 to 1993 in in Japanese, lets just say it is a lot to simply put in google translate. 

Edited February 4, 2021 by AerostarDriver

[hammdo]

I bet!

-Don

[carusoam]

@AerostarDriver...

Check out this thread...

Jeph has made some friends in aviation in Japan...

I found a Japanese pilot flying a Mooney on YouTube...  Jeph was in Japan looking for something to do...

Next thing we know... Jeph is flying in Japan with the Mooney guy from YouTube...

How small is the Mooney world?

-a-

 

[AerostarDriver]

Pictures posted.

[Gary0747]

Looks like residual adhesive?  Was the foam installed using self stick or additional adhesive?  If so perhaps the adhesive or surface prep is the culprit?   Also I thought the purpose of the original service bulletin was to stop corrosion of the steel tubes and the aluminum was not a corrosion problem. It sure appears to be chemical incompatibility with the aluminum.  Any way to trace it back to the manufacturer of the foam? Any number of things can create incompatibility. Blowing agents, fire proofing chemicals or the foam composition itself. 

[AerostarDriver]

51 minutes ago, Gary0747 said:

Looks like residual adhesive?  Was the foam installed using self stick or additional adhesive?  If so perhaps the adhesive or surface prep is the culprit?   Also I thought the purpose of the original service bulletin was to stop corrosion of the steel tubes and the aluminum was not a corrosion problem. It sure appears to be chemical incompatibility with the aluminum.  Any way to trace it back to the manufacturer of the foam? Any number of things can create incompatibility. Blowing agents, fire proofing chemicals or the foam composition itself. 

The foam has no markings of any sort and was hand cut and installed. I cannot find a log book entry that shows when it was done but it is a self stick foam from what I can tell. The process for removing it is extremely labor intensive. The foam can be dissolved with Acetone but the adhesive can be peeled off with mineral spirts, nothing else seems to be able to remove the adhesive better, we tried the usual suspects, denatured alcohol, acetone, MEK and mineral spirts. I have to give a shoutout to Mrs. AerostarDriver who has now spent about 30 hours total peeling the old foam out, removing the adhesive and then using wax and grease remover to prep the non-corroded parts for the correct foam kit to be installed.  

[carusoam]

I sent a page of the logs to a friend that has a background including Asian languages... 

Oddly enough... the characters in Japanese are often shared with Chinese...

They had difficulty with the blur... a typical iPhone challenge...

So i printed the page as clear as I could... See if I can make any headway that way...

Go MS!

Best regards,

-a-

[Dale Logsdon]

Looks like a problem with the glue.

Corrosion is only present where there is glue residue on the aluminum.

[AerostarDriver]

I guess my word of advice is if you do have black foam, maybe peel a little back at your next annual and take a look.

[N201MKTurbo]

I have the same black foam, but it isn't glued in. It is cut so it wedges between the tubes or just sits there between the plastic and skin.  It takes no time at all to remove it and replace it.

[N201MKTurbo]

Well, the up side is; I don't think any of those panels are structural. You can scrub off the corrosion, paint them and you should be OK.

I suspect moisture got trapped in there and caused the corrosion. That was the purpose of removing the fiberglass.

[MrsAerostarDriver]

I finally made an account!! I was the one who peeled and removed all the black foam. There seems to be confusion about glue and self stick. Just to clarify, the tan/brown glue you are seeing in the pictures my husband posted has nothing to do with the black foam, it is residual glue from the original fiberglass installation (this glue would not come off with anything I tried, however all the fiberglass was removed). The black foam was self-stick. 

That being said, the black foam is very different than the approved Mooney foam kit. The Mooney foam kit is significantly more porous and light as to not let moisture get trapped and has a very thick gooey anti-corrosive adhesive backing that fills in cracks and crevasses well. The black foam was not as porous and had a harder adhesive (on top of feeling cheap, plasticy, and heavy), so as some of you have noted it could have been the combination of the black foam with the old bumpy glue trapping moisture that caused the corrosion.

To rectify, that was the whole point of removing the fiberglass as to avoid moisture-induced corrosion on the steel frame. By replacing with alternative foam instead of the approved kit, you have the potential to create the same moisture-induced corrosion, except this time on the skins. I am a big believer in not cutting corners in aviation, it's expensive in the short-term but manufacturer's parts will save you on labor, money, and prevent damage in the long run if you intend to keep the plane for a long time. 

[PT20J]

2 hours ago, MrsAerostarDriver said:

I finally made an account!! I was the one who peeled and removed all the black foam. There seems to be confusion about glue and self stick. Just to clarify, the tan/brown glue you are seeing in the pictures my husband posted has nothing to do with the black foam, it is residual glue from the original fiberglass installation (this glue would not come off with anything I tried, however all the fiberglass was removed). The black foam was self-stick. 

That being said, the black foam is very different than the approved Mooney foam kit. The Mooney foam kit is significantly more porous and light as to not let moisture get trapped and has a very thick gooey anti-corrosive adhesive backing that fills in cracks and crevasses well. The black foam was not as porous and had a harder adhesive (on top of feeling cheap, plasticy, and heavy), so as some of you have noted it could have been the combination of the black foam with the old bumpy glue trapping moisture that caused the corrosion.

To rectify, that was the whole point of removing the fiberglass as to avoid moisture-induced corrosion on the steel frame. By replacing with alternative foam instead of the approved kit, you have the potential to create the same moisture-induced corrosion, except this time on the skins. I am a big believer in not cutting corners in aviation, it's expensive in the short-term but manufacturer's parts will save you on labor, money, and prevent damage in the long run if you intend to keep the plane for a long time. 

Great post and details  Sorry you had to rip all that stuff out -- it's a miserable job. Another point to consider is that some substitute foams may not be fire retardant. My 1994 M20J had the foam from the factory on the sidewalls but still had the fiberglass in the baggage compartment and ceiling. I decided to replace it all and ordered some from a MSC. I got flame cert info from Mooney to keep my IA happy. Mooney buys the fire retardant foam from one vendor and then sends it to another to have the adhesive applied. Then they have to do another flame cert on the finished product.

Skip

 

[A64Pilot]

take some of the removed foam, put it in water and squeeze it, if it absorbs the water like a sponge it’s open cell foam, and that’s possibly what caused the problem.

‘I’ve not seen the Mooney foam but hope it’s closed cell

[carusoam]

Welcome aboard Mrs. AD!

I’m glad you can join us.

You two need to work on your avatar pics...  

Best regards,

-a-