I was actually trying to find a picture without the inside layer, it would be kind of impossible to do with a tank unless you blew up some sort of blader inside to hold it there. One positive with patching tanks though is that the outside of the repair doesnt have to look as nice as a boat repair. Just be glad there isnt any kevlar in the original layup!!
I had previously coated the inside of my fiberglass tank with 2 coats of Caswell's but had to cut a clearance notch in the bottom to clear the carbs. Didn't have any confidence about sealing the notch from the outside so I cut off the top off the tank with a thin wheel. I'm glad I did as the coating had numerous pin holes where it hadn't sealed over little voids in the original tank surface. Very lightweight fiberglass cloth like is used on model airplane was applied with some more Caswell's on the inside. Hopefully this will add to the integrity of the coating. I glued the top back on after beveling the edges and applied a couple of strips of fiberglass with the same resin. Normal bondo repair after that. We'll see if it works.
I am speculating, as I don't have a fiberglass tank to mess with, but here are some things that I have thought about in reference to this project.
First, look at the directions of the resin...
Second, read them! Some resins will not stick to themselves unless there is prep in between coatings. Some stick to themselves well if the second coat is applied while the first is "green". It is good to know this characteristics of your resin so that you can plan your job accordingly. How much pot life do you have? This will let you know whether you can relax and have a beer during the proceedure or whether you need to be set up like a pit crew.
Then, what if...
You applied resin to the inside of the tank, put thickened resin along the cut edge, placed duct tape or similar over the seam and then turned the tank right side up. The coating of resin and thickened resin would form a slurry that would run into the seam and self-level. Once cured you could grind out a channel along the seam to apply cloth and resin to strengthen it. As near as I know fumed silica works as a thickener for vinyl-ester resin. It comes it brand names of Aerosil or Cabo-sil. If you can't find it, I would mail you enough for the job, I have an abundance here. If you place the resin and the silica in a large zip lock baggy mixing it is easily done and then you can nip the corner of the bag and squeeze it out like a cake decorator. It is important to know if your resin thermally reacts (does it get hot and kick faster in quantities), if this is so pot life will be decreased while working with the thickened resin in a baggy (that may melt if it gets hot and forms a big lump in the center). You can avoid this to a degree by laying the baggy flat or even place it on a bed of ice, but it would be best to make sure you are ready to use it right away when you mix it.
I've thought of the cut towards the top of the tank, versus the bottom. Ruled it out, as it's just extra work to clean it all up. Ditto for splitting it lengthwise, top to bottom! As for plastic causing a problem with the fuel... that's what we store our fuel in, in the garages. Plastic fuel cans! My greatest problem, is that when I do my father's tank, I don't EVER want to have to do it again. As such, I don't trust a single damned one of these chemical products out there, it being a false premise to consider 'this' sealer a success, simply because it 'held up' for 3 or 4 years. I do not think the tank is all that difficult... it's finding the RIGHT liner that seems elusive as hell. Jean apparently did his well, but I'd only wish he'd done it 10 years ago and could report it still holds up! It seems easy: make it permanent, or go with metal, aluminum, whatever.
Send me a PM of your email address, and I'll send a pic of what I mean from my earlier description. It's very much similar to some of the guys referring to lining as 'tabs'. Same concept.
Thanks heaps Russ lots to think about, I guess I hadn't gone that far yet until I finished prepping the tank but that's great, the catalyst I got with it is a different to normal il get the name later but it apparently some low ....... type that stops any air bubbles forming in the resin and tissue, after the resin is applied over the tissue I got a special roller to to roll it down to make sure the air bubbles are gone. I havnt heard of the thickeners that u mention Rusd what is the difference between using one and not Im not fully sure? But I think ur idea of putting some resin in the join with tape then turning the tank the right way up is a great idea, I guess this was like hobots JBWeld idea, I'm not sure what one would be better to use as I'm not sure of the qualities of JBWeld. Would the thickener help thicken the resin so it would sit in the 2mm gap between the joins? Thank you for your offer for some to Russ very nice, thanks. The guy at the composite place where I got my supplies said to use it between 16-25degrees celcius but I forgot to ask him about re applying if done after it dries or when still drying, will find out!
I don't want to come off like I am trying to be the tank expert here. I am not, Jean as an example has hands on exprience of doing one recently. But I have built a lot of stuff out of resins and different types of cloth or matt. I have never used vinyl-ester. So first thing I would do with some is mess around with it and figure out how it acts.
As for the thickeners, there are lots of different things you can put into a resin. Micro-ballons are like little ping pong balls to make it sand easily for fairing. There is stuff like hair that gives the resin some structure and bonding capability. Silica makes the stuff so it wont run or sag depending upon how much you put in. There are different types of silica but from reading on the products known as "fumed silica" such as Aerosil and Cabo-sil they are compatible with vinyl-ester resin. West Systems offers colloidal silica, which may or may not work well with vinyl-ester. It is my understanding that it doesn't stay in suspension very well. So again, I would experiment with some before using it on the tank. It would fill gaps but you would still want to use cloth to strengthen the joint after or during the glue up.
As for turning the tank right side up...if you got the consistency right, the stuff would self level in the bottom of the tank rather than drip like stalagtites. The key would be to first put unthickened resin on the areas to wet them out, squirt out a line of thickened goo that was stiff enough to stay put for the time it took to spread it but was loose enough that gravity would act on it during the curing process. My guess would be to keep the stuff cold while you put it together, roll the tank over and then warm it up with a hair dryer or light bulb. If you decide to roll the tank right side up, you are going to need to secure the bottom in place, so I would probably just use duct tape over the seam, most of it will peel off afterward but you might have to use acetone or sandpaper to get the last of it. It means you need to keep the outside of the tank pretty clean during the glue up if you want it to stick but I have used this often when I needed to keep resin from draining out of an area I was working on.
One of these days I will run across a fiberglass tank to experiment on. The darn things actually fetch a pretty good price even now so it is not high on my list of projects. I just like the challenge it presents. Regardless of what you decide to do, good luck with it and keep us posted on progress.
While gluing is on the mind, keep in mind the superglue scope of uses plus adding baking soda to bulk it up for fill ins and custom fairing shaping. Good shop and riding 1st aid item to keep in kit too. http://en.wikipedia.org/wiki/Cyanoacrylate