I have been researching an epoxy coating that is very similar to a barrier coating. It is NSP 120 and has been tested for water potability. Very thick, would fill in the pits. It is just the bottom of the tank that is bad, but I would probably coat the seams as well. I have a bow tank. Friend with same boat had to have theirs pulled out by a marina yard, then replaced....$1500, mostly for labor to get the tank out. Yikes! If I can preserve the tank, it sure would be my first choice, and since it doesn't leak yet, it seems the simplest solution. Any thoughts on the epoxy? Another forum post said the US Navy is using high grade epoxy coatings over aluminum.
Indeed NSP 120 is compatible for potable water, is used in various commercial applications.
Ive used it with limited results on a large aluminum tank.
1. You MUST provide lots of 'tooth' to the aluminum using 40-60 grit sanding discs, etc..
2. You really have to coat 100% the ENTIRE inside surface and no 'misses', because if there is any exposed metal surface and the water contains 'any' chlorine, aluminum chloride will eventually form 'behind' the coating and will 'push' the coating away from the metal surface causing even more aggressive lifting of the coating.
After 8-10 of service with that coating inplace, I replaced that 100 gallon coated aluminum tank with a stainless tank; but, if I were ever to do such a coating again, Id do a better 40grit sanding job, I'd probably add a layer of lightweight fiberglass cloth (for added strength) and with an extra coat of NSP-120 on top of the fiberglass to lessen the water intrusion through any 'holidays' in the coating. Inotherwords - building a tank in a tank, using the aluminum simply as a 'mold' for the new tank.
The coating has to be 110% perfect or it will eventually lift .... mine did after 8-10 years.
When I did originally coat the OEM tank, I had a 'leachables' test performed to validate the non-release (leachate) of 'organics' .... there were 'some' after the tank sat full of water over a long time. For the correction, I added a recirculating pump and small carbon packed filter to the tank, and simply 'stripped' the monomers, and other chemical fragments for several hours before using that water. A tank much less than 100 gallons would have a higher ratio of (low amine) epoxy contact surface to the volume of water contained with regards to 'some' leachables, probably more leachables than what I found.
NSP 120 is a seemingly good product, mix each component until its to the consistency of mayonaise before mixing the two components together and be sure to use the two pot method for mixing .... mix in one pot, remove that contents into a new container, then mix again ... so you get 'proper' and thorough mixing.