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Just ordered 2 quarts of ProSeal...

cderk

cderk

Well Known Member
I'm a little nervous. I just ordered 2 quarts of ProSeal today (or whatever the new stuff that Van's carries is called).

I'm not sure how I feel about this. For those of you who have built your fuel tanks from scratch, is there anything that you would have done differently? I'm planning on sticking with the stock fuel sensors (float type) and stock fuel caps.

I'm planning on priming the areas that are not inside the tank... I'm also planning on etching (using Stewart Systems EcoEtch) the areas that will need the tank sealant.

Is there any reason not to etch the entire inside of the tank? Even though its a larger area, it seems like it would be less work than trying to mask everything off and just etching areas where parts will mate.

Thanks
Charlie
 
Mask

I wouldn't etch the whole thing, because the Alclad will provide corrosion protection. The areas that are scuffed will be coated in proseal (or Flamemaster), so it's protected too. Have fun!;)
 
ppilotmike said:
I wouldn't etch the whole thing, because the Alclad will provide corrosion protection. The areas that are scuffed will be coated in proseal (or Flamemaster), so it's protected too. Have fun!;)
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An acid etch won't remove the Alclad layer.
 
Most just scotch bright where the ribs will be sitting to assist with bonding. I don't see much value in etching in fact, etching without a top coat isn't advisable and you don't want a top coat in the tank for obvious reasons.
My advice, go slow. Mix up enough pro seal to do a few ribs, then rest. It is very tempting to go for it and do one tank completely. With experience, it can be done, but the pro seal will start to set up and thicken if you're not moving fast enough. This can lead to inconsistent rivet sets as the layer of pro seal under the rib becomes less compressive, if that makes sense.
It isn't as hard as some make it out to be. It is messy and smelly and pro seal will get on anything and everything. It just isn't a lot of fun.
 
JonJay said:
Most just scotch bright where the ribs will be sitting to assist with bonding. I don't see much value in etching in fact, etching without a top coat isn't advisable and you don't want a top coat in the tank for obvious reasons.
.....
Click to expand...

Why not inside a fuel tank?

Also if you check the Pro-Seal spec sheet, even an etch and alodine on Alum. is acceptable.

You can sort of look at an etch as a really good microscopic level cleaning...:)
 
az_gila said:
Why not inside a fuel tank?

Also if you check the Pro-Seal spec sheet, even an etch and alodine on Alum. is acceptable.

You can sort of look at an etch as a really good microscopic level cleaning...:)
Click to expand...

I just don't feel a top coat inside a tank is a good idea. Might be just fine, but it doesnt make sense to me and if you did have any adhesions problems....
Etching covered in pro seal is a top coat. Etching without conversion and a top coat isn't recommended on exterior surfaces, if you believe AC-43-1b. Inside a tank? Might be just fine too, but not for me.
I would say "best practices" don't always follow what may or may not be technically correct or possible.
I don't know anybody who has painted the inside of a tank. I wouldn't buy one that had.
 
As previously mentioned, do not etch anyting inside or outside the tank. A simple SS wire brush is all you need to scuff up just the area you will apply proseal.

Prime the outside ribs and rear baffle after the tank is done and you have done the leak check. I also put 15 gallons of 100LL in each tank and let then sit for a month or so in different orientations (tanks are on a table, not the wing). This way you will find out if you have a weeping rivet or not - they will not show up via a leak check.

Carl
 
JonJay said:
Most just scotch bright where the ribs will be sitting to assist with bonding. ... My advice, go slow. Mix up enough pro seal to do a few ribs, then rest. It is very tempting to go for it and do one tank completely. With experience, it can be done,... It isn't as hard as some make it out to be. It is messy and smelly and pro seal will get on anything and everything. It just isn't a lot of fun.
Click to expand...

When I did my tanks I did one rib per evening. ... I was never tempted to "go for it and do a whole tank." Not once. A few times I was, however, tempted to gently lay the partially constructed tanks down on the garage floor and drive over them multiple times with the car. And I might have if that wouldn't have meant getting proseal all over the car.

Seriously. It's not that hard to work with but it does get on everything. Make sure you wear old clothes and prepare the surrounding work space for the mess. Of course wear gloves and a hat and be as slow and methodical as you can. Whatever. You're still going to get it in your face or ears or hair at some point. Best to just yield to that fact up front. It comes off eventually.

One of the best days of my build was finding no leaks in the tanks.
 
Some great advice, thanks guys. If you had to do it over again, anything you'd do differently (other than have someone else do the tanks)?

Thanks again!
 
Advise

cderk said:
Some great advice, thanks guys. If you had to do it over again, anything you'd do differently (other than have someone else do the tanks)?

Thanks again!
Click to expand...

Some may disagree but I enjoyed building the tanks. In the end it was just another task.
Read the various methods. I used the Fay Sealing method. Mine held 27" in a manometer for a month and I called them good. I documented the process in my blog.
Regarding etching, I agree with a scuff, clean and assembly. You want the window between scuff and application as narrow as possible. A few hours if you can. That's the window for Aluminum Oxide formation. AO is hydroscopic. Proseal probably doesn't care but paints don't stick to it.
I got everything ready to assemble, cleko ribs, drew lines with a sharpie then disassembled. Scuff inside the lines clean with MEK and assemble. Only time I used MEK.
One piece of advise. Don't wipe the outside with MEK. Just wipe excess off with with a square of shop paper towel. I cut shop paper towels into small squares and used lots of them. It really helped reduce mess.
 
I also enjoyed building the tanks. I assembled the tanks a rib at a time. Sometimes two or three per evening. I'm not sure who came up with the method but I would 100% cleco the ribs set in proseal and then come back the next day and wet set the rivets. I used a syringe to put a little proseal in the dimple hole, then dip a rivet in proseal, cover with rivet tape and buck. Then go to the shop side and swirl proseal around it. No leaks
 
I built 2 main tanks plus 2 aux tanks (RV-7) using 1 can of Flamemaster. Sealant stays in the freezer unless I'm actually using it.

As others mentioned, 1 or 2 ribs per session was about right for me. I never mixed more than a golf ball worth at a time; usually less. I did my riveting the old fashioned way, but with much less sealant than most use, on the advice of a 2 time builder. Tiny donut around each hole, insert the rib, dab in the dimple, dip the rivet, set, cover the shop heads when done. End ribs obviously require a fillet on the inside.

Again on another's advice, I used cheap (thin) quart ziplocs to mix & dispense. Turn the bag inside out, weigh mix 'on' the bag, invert, squeeze out the air, zip shut, mix with a roller (short length of 1/2" pvc pipe). Roll the mix to a corner, snip the corner, and use like a cake decorator bag. No syringe loading involved; very little waste, and very neat/clean.

YMMV...

Charlie
 
I built four tanks (main/aux) using three and a half pints of B4 sealant from Spruce. The working time is longer so I was able to do three ribs at a time.

I scuffed the rivet lines with scotchbrite and cleaned with MEK.

I mixed up a batch at a time using a digital scale, and applied generously to the ribs with a popsicle stick like I was frosting a cake. Trying to apply it with a bag or syringe just wasted sealant, as a bunch was left in the bag or got all over the side of the syringe.

I wet-riveted, as I found it made no more or less mess waiting overnight. If the rivet hole was full of sealant, I just inserted the rivet; if not, I added a bit with a toothpick (dipping rivets just got sealant all over my fingers). Once riveted, I covered the shop heads and filleted the edges with a gloved finger.

I also used a generous fillet on the baffle, applying it just aft of the rivet holes instead of in front, then fillet sealing the aft edge after installation. I used spring clamps in addition to clecoes to make sure I had good clamping to the skin.

Just another technique; use what works for you. I'm of the opinion that adding a couple more pounds of sealant and using it generously is worth the piece of mind, and it's more or less how we do the tank, pressurization, and anti-corrosion sealant on the big airplanes at work. My process is messy (I'm a messy worker on anything, really) but my tanks held air.
 
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I used the Brown tool applicator gun and really liked it. Those are the only tanks I've built, but it was super easy and clean. Have lots of gloves and just embrace it. It's really not that bad!
 
A 60 mil syringe worked for me. And a 10 to 1 homemade balance. Shot wet rivets immediately. Like someone said above, its pretty easy to build a pair of tanks with one quart. Yes, a freezer is your friend for both mixed and unmixed proseal.
 
Excellent feedback. I did see the suggestion in the build plans about using a syringe to apply the proseal. seems like a good idea. i would think that its a pain in the neck to stuff the proseal in there, but the syringe seems like it would be less messy when applying.

I guess I would attempt the 1 to 2 ribs per session approach. seems like most folks have had good luck using it. i need to get this done in the next month. its starting to get colder in the northeast and i'm going to have to do this in my unheated garage to minimize the fumes in the house.

charlie
 
If I were making my tanks today, I would use higher quality senders than the ones included with my kit (early 1990's vintage wing kit). The senders I have seen from EI and Cirrus are much more robust. They both have better shaped floats to minimize empty and full errors. I would also recommend the programmable gauges to compensate for the inherent nonlinearity of a float type sender.

Also, I would recommend you alodine all the tank parts. Once an aluminum part is etched and alodined, its surface remains stable for a long time and will provide a good surface for sealant adhesion. Even if you " scuff as you go", its hard to match the adhesion quality of the alodined surface. You will note that the data sheets from most (or all) of the polysulfide manufacturers provide performance data based on alodined aluminum substrates. For example: http://www.ppgaerospace.com/getmedi...fc0-bacdee414245/pr_1440_class_b.pdf?ext=.pdf

Good luck,
 
Thanks again for all the great tips. So reading all of this and what i can find online, am I correct in that there are really two schools of thought...

1. Dab proseal on the rib flanges around the rivet holes only
2. Smear proseal on the whole flange of the ribs

Thanks
 
cderk said:
Thanks again for all the great tips. So reading all of this and what i can find online, am I correct in that there are really two schools of thought...

1. Dab proseal on the rib flanges around the rivet holes only
2. Smear proseal on the whole flange of the ribs

Thanks
Click to expand...

I kind of did both. I "buttered" the flange but also created a fillet (mostly with the squeeze out from the flange) between the flange edge and the tank skin. Finally I encapsulated the rivet shop heads with a dab of proseal.
 
cderk said:
Thanks again for all the great tips. So reading all of this and what i can find online, am I correct in that there are really two schools of thought...

1. Dab proseal on the rib flanges around the rivet holes only
2. Smear proseal on the whole flange of the ribs
Click to expand...

IMHO "dab proseal on the rib flanges around the rivet holes only" is asking for trouble. There's a reason standard industry practice from small airplanes to airliners is to seal the entire mating flange (fay surface), and then wet-install fasteners and seal the edges of the flange and the fastener shop heads. You have a much greater margin for error and much-reduced potential for trapped moisture inducing corrosion.
 
Charlie,

If you could do a 'scientific poll', I'm sure that you'd find my technique (sealant only around the holes) is used in a very small minority of builds. Most butter up the entire rib, then fillet both sides after riveting. That obviously works, but...

After my friend explained his technique, I realized that all that sealant in that ~1" *between* the rivets wasn't doing anything to seal up that 3/32" dia hole.

The biggest danger when using 'my' technique is that if the sealant is already getting 'stiff', it *might* try to make a bulge around each hole. But if it's that stiff by the time you rivet, you may not get good adhesion, anyway. On the flip side, buttering the entire rib can make it more difficult to 'nest' the rib into the proper position to get the holes lined up.

It really comes down to what you're comfortable with.

IF you could be sure of a good seal in the dimple, then all you would need is to wet the rivet before shooting it.....

Charlie
 
I would get a Semco pneumatic gun. Started without it, and then when I had it I really appreciated it. I got one on eBay with the 2.5 oz size cartridge. I found a source here for unused cartridges and they are reusable. After I mix some proseal with a $1 plastic cutting board and a cheap pink bondo paddle I load the cartridge with a tip screwed on it. Load in the semco gun and use as needed. If I don't use it all I put the gun and cartridge in a bag in the freezer so it will keep a few hours longer for dabbing rivet heads at the end of the project.

I did 2-3 ribs at a time this way. Fay sealing (good threads on that here already).

When I was done I unscrewed the tip, and pushed out all the proseal on my mixing board. Then I used a pencil to push the plunger back out - very gooey. But then after it all dried in a few days all the proseal peeled off the plunger, out of the tube, and cleaned up well. The plug in the tip can be had by taking a dental pick, inserting in cured plug, and pulling the plug out. It doesn't stick to the plastic. I cleaned the board and paddle after curing too. Getting wet proseal off these really is hard but dry proseal just peels.

First time I did it I left the plunger in the tube - never did get it out! One tube thrown away. Now I have four tips different sizes on the end.

This kept my proseal very neat and easy to apply. Really worth the money. Later in the project I've had to proseal the firewall and side skins and things and I just do a small batch the same way no fuss.

Keep your unmixed proseal in the freezer - it can go a year or more past the expiration that way. I only used in-date proseal for my tanks but for all the other odd jobs since then I've not bought more and it mixes/acts/cures like it should.
 
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JDA_BTR said:
I did 2-3 ribs at a time this way. Fay sealing (good threads on that here already).
Click to expand...

Just a nitpick - "fay sealing" means sealing the "faying surfaces" - that is, the entire contact area. It has nothing to do with whether you let the sealant set up some before installing fasteners.

rv7charlie said:
After my friend explained his technique, I realized that all that sealant in that ~1" *between* the rivets wasn't doing anything to seal up that 3/32" dia hole.

The biggest danger when using 'my' technique is that if the sealant is already getting 'stiff', it *might* try to make a bulge around each hole.
Click to expand...
You're almost inevitably going to get some kind of pinhole or void in your sealant, whether it occurs during installation or later on (i.e. when the sealant disbonds). If you only have a little sealant around the holes, it doesn't take much of a defect to start a leak. Plus, all of the area between the rib flange and the skin that isn't sealed will collect moisture and debris and foster corrosion. By sealing the entire flange you create a greater distance that any defect would have to extend before it can cause a leak.

On large aircraft, everything gets sealed, not just the fuel tank structure. It's sealed to help prevent corrosion and hold pressure (in the pressurized areas). And in all of those applications, the entire faying surface is sealed, not just the areas around the fasteners.


It's one thing to save a little primer and only paint the mating surfaces between parts. But sealing your fuel tanks is nowhere to try and skimp.
 
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