Fuel tank leaks.

[rrodriguzzi1]

Ok. Here I go with a bit of information on fuel tank leaks / sealant. I did this type of work thru out my almost 30 years of experience doing sheetmetal work. At most places we had a crew taking care of sealant removal only. In this case I am doing everything myself. Just more work for me. This one tank in specific, had a patch / seal job or work done back in 1993. Not to criticize, but for just for informational purposes only. It looks like there was no adhesion promoter applied to the existing sealant on the fuel tank supply line. That’s the light gray area. Also, at the time they did this work, they used the wrong size ( longer ) screw lengths for the access plates, creating leaks on the access panels. Hard to determined if the initials leaks were fixed in the first place or if it was a failed attempt creating even more leaks in the process. In any case. I am sure whoever did it had good intentions. I want to believe that a properly done patch job should last a long time. The only reason I am doing this tank is because of the number of previous patches done to it in the past. The pictures are of the initial work. Some of this pictures are vey graphic. Mooniac discretion is advised. I will put together a nice set of pictures as progress is made. Also, notice the bad rivets, done by the factory back then. That was probably done on a Monday morning. There’s about five or six rivets that need to be replaced. I added protection to the wing after this pictures. I am planning on repainting the inboard section of the wings anyways after I found  the paint codes in the logbooks. I will be using PPG products and the sealant stripper is PolyGone-310-AG. Related, unrelated. I remember way back fixing a series of Aero Commanders and King Airs that had serious pressurization problems. Whoever tried to fix them applied sealant over existing sealant. That of course didn’t work. The place doing the work back then didn’t know about any adhesion promoter, so more new sealant was added without the promoter. And in my experience I have only used promoter over a nice clean surface, never over existing sealant. But, doing some sanding on the existing sealant and promoter should work. By the way the adhesion promoter information can be found in the PPG Aerospace website. I hope that wasn’t too boring. 

[Shadrach]

Wow. The last person that was in there definitely favored quantity over quality.  That tank has mostly factory sealant and it looks to still be in reasonable shape. That being said, original sealant sometimes looks fine until the top layer of red PR-1005 is removed and then it crumbles like dry mud.  The up shot is that very old sealant can be relatively easy to remove compared to newer sealant. I’ve never found an adhesion promoter to be necessary.

[N201MKTurbo]

Sealant should never be placed over old sealant to fix a leak. You should always clean the old sealant off down to clean metal. 
 

I realize that at the edges of the repair there will always be some overlap of new sealant over old, but make it at non critical areas.

The proper repair procedure is in the maintenance manual. They are very specific about how to apply the sealant. There is no mention of surface modifiers or primers. It specifically states that you must clean the surface with MEK just before the application of sealant using a new cloth wipe. 

[N201MKTurbo]

When doing a brush coat, you need to thin he sealant so it brushes smoothly. It is hard to get it to adhere and fill all the voids if it is too thick. Besides if it is too thick it won’t level and looks horrible like in the pictures. You need to test the brush sealant on a piece of cardboard, wood or metal so you know that it Is properly brushable. It looks so much better when you do that. It looks just like the original sealant job.

[rrodriguzzi1]

That is the worst part. Removing the sealant. 

[N201MKTurbo]

Also, on the sump drain, it does no good at all to put sealant around it. It just makes a mess and clogs the drain. The only way to do it right as to drill out the rivets holding it in, take it out and clean it till it looks new. Then clean the area around its mounting to bare clean metal. Mix up a little dab of sealant and smear it on the bottom of the drain and some on the metal where it mounts. Then rivet it back in. Put a little sealant on the rivets before you set them. That’s all you need. Any other sealant is just a waste.

[rrodriguzzi1]

Right, that’s what I was planning on doing. Thanks 

[carusoam]

Nice work rrod!

the more details… the better!

 

The cool thing about this project…

The Mooney can end up better than new!

 

Stripping sealant out of every nook and cranny takes a ton of effort…

 

But, it is worth it!

Best regards,

-a-

[rrodriguzzi1]

 I will post progress as I go. Doing this part time. 

[rrodriguzzi1]

It does. You either like to do this type of work or you absolutely not. 

[Mooney-Shiner]

On 11/4/2022 at 9:01 PM, N201MKTurbo said:

When doing a brush coat, you need to thin he sealant so it brushes smoothly. It is hard to get it to adhere and fill all the voids if it is too thick. Besides if it is too thick it won’t level and looks horrible like in the pictures. You need to test the brush sealant on a piece of cardboard, wood or metal so you know that it Is properly brushable. It looks so much better when you do that. It looks just like the original sealant job.

Thinning of the sealant is a little tricky.  I think its not recommended to thin the sealant with anything but toluene. I learned that the best way is to get two types of sealant to prevent any need for sealing:

1. Class A that is self-leveling to apply on horizontal surfaces.

2. Class B that can be applied to  the vertical surfaces without sagging and is more widespread in supply chain.

I used the FlameMaster and had pretty good results. 

http://flamemaster.com/cs-3204-class-a-b-c 

Apply the top protective coat afterwards. Verify repair with Plexi and vacuum. 

[Shadrach]

34 minutes ago, ukrsindicat@yahoo.com said:

Thinning of the sealant is a little tricky.  I think its not recommended to thin the sealant with anything but toluene. I learned that the best way is to get two types of sealant to prevent any need for sealing:

1. Class A that is self-leveling to apply on horizontal surfaces.

2. Class B that can be applied to  the vertical surfaces without sagging and is more widespread in supply chain.

I used the FlameMaster and had pretty good results. 

http://flamemaster.com/cs-3204-class-a-b-c 

Apply the top protective coat afterwards. Verify repair with Plexi and vacuum. 

The maintenance manual specifies MEK for thinning. Acetone works as well.

[Kelpro999]

I feel your pain. I have the same problem, except they spread massive amount of newer gray stuff  over everything. Poly-gon doesn’t seem to work at all. Paint stripper works on original and seal coat- somewhat.
 In your photo with the scraper, there’s a  fairly large gap between the lower spar strip edge and rib that is direct into the cabin (end of scraper pointed directly at it). Extra attention is required there.

 

[Shadrach]

11 minutes ago, Kelpro999 said:

I feel your pain. I have the same problem, except they spread massive amount of newer gray stuff  over everything. Poly-gon doesn’t seem to work at all. Paint stripper works on original and seal coat- somewhat.
 In your photo with the scraper, there’s a  fairly large gap between the lower spar strip edge and rib that is direct into the cabin (end of scraper pointed directly at it). Extra attention is required there.

 

Poly-gon works but it needs hours to break sealant down, and takes multiple applications. Paint stripper is corrosive to aluminum, I would avoid using it. 
 
Best remove as much as possible mechanically and use poly-gon to finish. I make scrapers from wood and plexiglass. 

[Browncbr1]

Polygone on then come back the next day and remove.   Repeat until all poly is gone. 
 

beats the heck out of scraping for hours.  
 

[rrodriguzzi1]

Polygone works. You have to have the right temp and lots of patience. The reason I mentioned temperature is because I am located in a cold weather area. This would not matter in hotter or warmer environments.  Works best with the original sealant. It doesn’t do well on the patches. I had to pull or scrape them off. Lots of patience. 

Edited November 9, 2022 by rrodriguzzi1
Added information

[N201MKTurbo]

MEK will soften the sealant and make it scrapable. It won’t dissolve it, but it will soften it. 

[Kelpro999]

2 hours ago, Shadrach said:

Poly-gon works but it needs hours to break sealant down, and takes multiple applications. Paint stripper is corrosive to aluminum, I would avoid using it. 
 
Best remove as much as possible mechanically and use poly-gon to finish. I make scrapers from wood and plexiglass. 

I’ve done testing with poly-gon over variable time and temp ( days @ 70-95f) with poor results although it seemed old- small bottle from spruce - and kind of thick like some stage of drying. 
 I had better luck with Solvent Kleene D-Zolve 1533R paint remover. It’s very safe on aluminum and steel with no hydrogen issues. Remove paints very well and somewhat reusable before it dries , stays wet for days if thick enough. 
  Images of D-zolve test 

[Shadrach]

12 minutes ago, Kelpro999 said:

I’ve done testing with poly-gon over variable time and temp ( days @ 70-95f) with poor results although it seemed old- small bottle from spruce - and kind of thick like some stage of drying. 
 I had better luck with Solvent Kleene D-Zolve 1533R paint remover. It’s very safe on aluminum and steel with no hydrogen issues. Remove paints very well and somewhat reusable before it dries , stays wet for days if thick enough. 
  Images of D-zolve test 

Checked out the website.Looks promising. If it strips as easily as it looks, I’d be tempted to completely strip and reseal in my hangar.

[Kelpro999]

2 hours ago, rrodriguzzi1 said:

Polygone works. You have to have the right temp and a lot of patience. Works best with the original sealant. It doesn’t do well on the patches. I had to pull or scrape them off. Lots of patience. 

Problem is… everything looks like a patch 

[Kelpro999]

7 minutes ago, Shadrach said:

Checked out the website.Looks promising. If it strips as easily as it looks, I’d be tempted to completely strip and reseal in my hangar.

That test was on what looks like four different sealants in my tank. You can see curling of edges on old patch and complete removal of red seal coat but it had a hard time with newer sealant , like not at all.
 They’ll  send you a free pint for testing- recommended, if you ask. 
 I did a complete paint removal on the ramp one section at a time with D-zolve. Pleasantly surprised how quickly I ate an elephant.

[ArtVandelay]

 I had better luck with Solvent Kleene D-Zolve 1533R paint remover. It’s very safe on aluminum and steel with no hydrogen issues. Remove paints very well and somewhat reusable before it dries , stays wet for days if thick enough. 

Great, except you’ll need to repaint the wings.

[Jsno]

I had a tank that had trees like yours.  The previous fix was to smash coat it.  The fuel intake screen was half closed up from this and the drain holes in the ribs were covered.  I used polygon with a little success.  The splash coat had to be dissolved with MEK first though.   I had better success with Stewart Systems paint stripper that I had left over form a previous project.  I then primed and resealed the areas with BMS 1828, a two part epoxy sealant.  Still finishing other things on the aircraft so in the future will find out how well I did..  

[Shadrach]

4 hours ago, ArtVandelay said:

Great, except you’ll need to repaint the wings.

Why? If handled properly it should not touch paint. 
Poly-gone also eats paint very efficiently. I had a single drip thrown from a brush hit paint. I now have a small drip sized area of bare aluminum. 

[Shadrach]

20 minutes ago, Jsno said:

Sorry about previous post.  No trees in my tank!

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