Tank Sealant input

Hi All-
I'm still working on sealing up my tanks ... I'm thinking of doing something "unconventional" / overkill & I'd like a little input from the peanut gallery . Before installing the rear baffle, I'm serously thinking about "painting" over all of the joints with a CLASS A-2 sealant. I'm using the PPG-Desoto sealant so I'd obviously stick with the same sealant but the lower viscosity class for painting. I know most are going to say this is overkill for a properly sealed tank but I'm thinking this may be a cheap (addtional) insurance policy against any current / future leaks while this is all open. I'd love to hear your comments on this.

As always thanks for your feed back guys!!!

I always remember George Orndorf's advice: "If you look at the tank and you say 'that CAN'T leak, ' it probably won't. If you look at it and say, 'I don't think it will leak,' it probably will."

Do what you need to do.

Thank you Bob. I think no matter what I do, I'll look at it and say "God, I hope this doesn't leak" fingers crossed! You just hear so many stories about weapy rivets etc. I just want to do everything I can (while I can) to ensure I don't have a problem down the road. For a $160 bucks, I'm thinking it's cheap insurance to paint Class A sealant over all of my completed joints. Probably not needed but what the heck, I only want to do this once... I wonder if anyone else has done this or thought abiout it.

Any chance this painted sheet could peel off and plug your intake?

Be sure to research the old problems with 'slosh' sealants. Knowledgeable people often say that the real issue with the sloshing sealants wasn't the sealant itself, but that when the tank was built, only the faying surfaces were carefully cleaned/scuffed. The large areas between the joints weren't prepped for sealant, so there was poor adhesion & over time, it came off in sheets. The same could apply if you're painting it on; be sure that the entire area that gets the stuff is prepped properly.

Having said all that, remember that the aluminum doesn't leak. The only place that the tank can leak is where there's a path to the outside. If you run a bead of regular sealant around the intersections, that does it. Anything applied more than a fraction of an inch away from the joint isn't sealing anything.


FWIW,

Charlie

Maybe not

I'm not seeing it. If you scuff and clean (very, very clean) the parts, use a liberal amount of sealant and encapsulate the shop heads I do not see where painting the joint adds anything to the equation. The only concern I had when building my tanks was at the rear baffle and I don't know how you would paint those seams.

I didn't, and wouldn't, use a class A top coat unless I was chasing a seriously elusive leak (which is the only time I have used it).

If you do decide to use it, make sure you prep all the surfaces really well.

Do it

The A2 is simple said, brushable pro-seal. It is a standard process to "topcoat"on big jets, and what I did on my -4 tanks. I think some readers of this post are imagining an actual paint. I used PR1422A2, there is also A1/2, which cures quicker.

The shops I'm aware of which reseal Mooney tanks use the brushable proseal as the final step. I'd say it is a good idea if you have the time and discretionary funds.

I used 3/4 of a qt on each 30 gallon tank. I sealed all joints with regular proseal with at least 1/8" overlap, then went over with PR-1005-L. Proseal does add strength to the joint. Proseal two prepared pieces together and do a pull test. Anything to help prevent leaks during normal operation or a crash is a good thing. I have not had the first bubbled paint or blue stain.

A proseal

My instructions at work are assemble wet B2, two coats A2, no leaks. My supervisor retired after running a sheet metal depot for the Air force for many years. I intend to do this with my tanks.

This may be per the manual. It's been 6 years so I don't remember what the instructions said. Sanded fay surfaces. Laid a bead along the rivet line. Installed rib. Riveted wet. Dabbed the shop heads. Lastly formed a filet of sealant on both sides of the rib flange (with fingertip). I have subsequently learned from my son (Navy AME AD1) that spit works excellently as proseal release for fingertiping. I have used that advice on all proseal work after the tanks.

Class A's not ment for topcoat, it's a basecoat sealant...

Walt said:

I didn't, and wouldn't, use a class A top coat unless I was chasing a seriously elusive leak (which is the only time I have used it).

If you do decide to use it, make sure you prep all the surfaces really well.

Click to expand...

I have worked with A and B class PPG-DeSoto sealants for more than 8 years on a weekly basis, sometimes everyday and I will say that topcoating with an A class sealant is a very bad idea. I only deal with it as a sealant used with Jet A and JP8, but it breaks down very readily after 2-4 years if consistently submerged and drastically less time if used in fuel tanks that that are not usually full (such as an auxiliary or extended range tank). It is, as Walt was leading to, used for very tight faying surface leaks and tank boundary leaks where the leak entrance point from the tank is not exactly known or hard to get to. That being said, your intentions for topcoating the rivets would be much more successful by using PPG?s B-2. It is not as easy to brush on as the A class sealants, but when thinned out with small amount of MEK, will be easily spread out in the areas you are working with. PPG also sells ?Adhesion Promoter? that goes with their sealants, commonly known by those who use it as ?smurf piss? that I ALWAYS use when laying down sealant. They have it in very small brown glass vials and comes with the sealant if you request it. If you are going to lay it down on top of Proseal, I would recommend that you lightly scratch the coat of Proseal with a metal brush, just enough pressure to take the shine out of it, then wipe the sealing area clean with MEK, then lay the promoter down extending one inch beyond the areas you will be sealing, and finally lay down a nice coat of B-2 in a swirling motion with your brush to work out any air bubbles that may have been formed between the two layers while laying the sealant. It will last longer than the plane will if done right. Just my $.02

You guys are all awesome!!! Thank you for the input! I really appreciate the different points of view! This type of conversation is one of the main reasons I decided to build an Experimental. All I can say is my plane will be built better than those flight-school tin-cans I wrenched on in college

Carefull!!

rzbill said:

I have subsequently learned from my son (Navy AME AD1) that spit works excellently as proseal release for fingertiping. I have used that advice on all proseal work after the tanks.

Click to expand...

I guess this is OK unless you're eating the stuff. For many years working on transport category aircraft I just dipped my rubber-gloved finger in liquid soap such as Dawn and used that to finger smooth sealer in tanks, around anntennas, leading edges etc. A damp cloth removes the soap after everything sets. Try it - you'll like it.

dhammer said:

I guess this is OK unless you're eating the stuff. For many years working on transport category aircraft I just dipped my rubber-gloved finger in liquid soap such as Dawn and used that to finger smooth sealer in tanks, around anntennas, leading edges etc. A damp cloth removes the soap after everything sets. Try it - you'll like it.

Click to expand...

WOW. A bunch of great tips!!! Honest question here though. Are you guys not worried about soap, spit or oils from your skin interfering with the sealant's bond or curing properties? I know its the outside surface of the sealant you are working with here but I'd think the contaminates could affect the sealnt in some adverse way. I'm spending a ton of time preping / cleaning the surfaces and I'd hate to reinterduce additional contaminates. Is this a dumb question?

rzbill said:

I have subsequently learned from my son (Navy AME AD1) that spit works excellently as proseal release for fingertiping. I have used that advice on all proseal work after the tanks.

Click to expand...

+1, The good old spit on the sealant and lightly run your finger down the fillet works like a charm, I have personally never tried the soap trick.

Daniel S. said:

I'm spending a ton of time preping / cleaning the surfaces and I'd hate to reinterduce additional contaminates. Is this a dumb question?

Click to expand...

Good concern, but in over 30 years working on corporate jets is has never an issue for me. For instance we have to make fillet seals around the leading edges, fairings, and antennas after removing them for inspections. Most aircraft call for 890-B2. We clean the surface with MEK then define the area with masking tape. The sealer goes on with a popcicle stick or applicator directly on the cleaned surface as close to the final profile as possible. You then use the soap trick to smooth it out then pull off the tape while still wet. The soap only touches the outside of the sealer and not the airframe under it. A final light run down the sealer with the soapy finger before it sets gets rid of the tape ridge. After everthing is dry any sealer on the outside of the fuselage gets wiped down with a wet rag and touched up with a brush so the sealer matches the paint.

I can honestly say in all these years I've never had sealer that did not stay stuck and this is on aircraft fly through rain and everything else at over 470 kts. No need for all this smoothing inside a fuel tank. Just make sure everything is clean and make your fillets with a popsicle stick. JetA is kerosene and we just wipe it off with MEK and paper towels before application without having a sticking problem. Get some of that stuff on your oily fingers then tell me it won't stick to everything.

Don't use mechanics red rags. They are cleaned in solvent and full of oil. Most manufacturer's warn not to use the B1/2 sealers if it touches plexiglas as the chemicals in it can start crazing. Use B2 instead.

Take all this FWIW

Don

Daniel S. said:

....Honest question here though. Are you guys not worried about soap, spit or oils from your skin interfering with the sealant's bond or curing properties?.....

Click to expand...

Fair question. I worked to (proseal) Milspec at McDonnell-Douglas for a lot of years. Strictly speaking, we were not supposed to use water, soap, spit, or any other foreign material when smoothing out proseal. Those unapproved tricks do work very well and the fact is, many shop personnel have been known to use em but first making sure the boss or no one from the engineering department was watching.

I'd be more concerned with the well meaning advice that is okay to thin proseal with MEK. Simply contact any proseal manufacturer such as Morton Thiokol and they will likely tell you toluene is the only approved thinning agent. That said, many builders do thin proseal with MEK but that practice may introduce an unknown I'd be personally reluctant to flirt with.

Rick6a said:

I'd be more concerned with the well meaning advice that is okay to thin proseal with MEK..

Click to expand...

I fully agree Rick. Thank you for looking out. I wasn't going to say anything on that topic because I truly enjoy hearing all of the differing opinions & techneques etc. I've already done my research on that topic & have toluene sitting here incase I do elect to do any thining (max 15% by weight).

I will say I know someone who thinned ALL of the proseal in his tanks with MEK. Not for me though

One suggestion I really like is using the PPG PR-148 adhesion promoter, which I will be doing going forward.