Making/Sealing Integral Water Tanks

[CapnK]

This is something I'm doing as the first step in Katie Marie's overlong :) refit. I want to make the under-sole bilge area, and the under-settee areas on each side of there, into integral water tanks. This will make the best possible use of the space for tankage, keep the weight low and in the middle, and provide a measure of safety in that if ever she is holed in these areas, water ingress would be contained or held to a minimum.

The common way to do this seems to be to build the space, then coat the interior with a food grade epoxy sealant which my research shows to sell in the $200 per gallon range.

So I figure there's got to be if not a better way, then at least a cheaper way. ;D

My first thoughts were to find stainless steel in a very heavy duty foil type thickness (but not so un-malleable as say, roof edge flashing material or soda can), mold it into the space, joining edges and seams with a food safe grade of silicone sealant/adhesive.

Insert hours of research and thought and web searching for suitable materials...

So then I realized why bother with that bit of thin metal lining, why not just basically smear and seal the interior of the compartment with silicone? Sort of make an "in-place water bladder"...?

(Right now Craig Amos/Faith is having convulsions... ;D )

Which led me to trying to find a rubbery coating that would do that. I did ponder using regular silicone caulking and a squeegee or spatula to smooth it along the walls of the tank, but I think that would make for non-perfectly-smooth areas that could/would promote algael (is that a word?) growth. I also pondered thinning the caulking in some way to make it brushable or rollable. Then I thought about the "As Seen On TV" stuff named Flex Seal. A-ha!

Their 'Liquid' product seems as if it would fit the bill, they say it is safe for use on rain barrels, but I couldn't find any specific references and a call to their company didn't give me a lot of faith that it has been used that way. The last nail, so to speak, was someone saying that after a couple of years, their product dries out and begins flaking. What a nightmare that would be if true. I don't want to even risk it.

So i looked for other stuff.

Found this product called "Ames Blue Max" that seems perfect. It's water based. Company rep says it's used to line cisterns in the south and Carribean, and fine for use where immersed in water, and it has a strong adhesive bond/strength as well. So I'm gonna use this as my tank lining, and I think it'll do the job perfectly. The only caution he had was that it is not UV resistant - a non-issue buried deep inside a boat, I should think. :)
Best - it's $55 per gallon, which covers 100 sq feet.
I'll update here as I use it. Here's some video:

https://www.youtube.com/watch?v=yXF-XK9EkVI

https://www.youtube.com/watch?v=kar_Ts3Nv90

[Lars]

james baldwin has several videos on this. i think he uses an food safe paint to coat the tanks. i would check with him and take his advice

[SeaHusky]

I will be very interested in your results! I plan to do the same (tank under sole) When I have done everything else.
I have used a squeegee to smear silicon when doing fish tank scapes and it is as you guessed, messy and non perfect.