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Old 30-07-2018, 18:59   #1
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Join Date: Feb 2017
Location: SW Florida
Boat: Morgan, Out Island, 49
Posts: 2
Leaking tank - water - aluminum - Morgan 49 - Sodium Silicate

I have a 200 gallon aluminum water tank on my Morgan 49. About 2 years ago, the tank started to leak so badly that it only took about 2 hours to completely empty. I really started to get bummed out because replacing the tank would have been really disruptive (I'm a live aboard and the tank is really built into the boat), and would have cost a lot of money. For various reasons, putting a bladder in the tank wasn't looking good. That's when I discovered what are broadly called sloshing compounds. Traditionally, these are used in aircraft (where some of the tanks are a part of the plane), by putting something like tar and a solvent into the tank and sloshing it around. As the material leaks out the solvent dries and slowly plugs the leaks. This works great for fuel tanks but water tanks need to use food grade materials.

First I tried something called MircoSeal, which is a polymer dissolved in acetone. First I spent several weeks drying out the tank by putting a bilge fan on the filler and taking off all the other fittings. Then I turned off the fan, put a gallon of the double concentrated material in, and got all of my neighbors to come by and jump up and down on the boat. Because the boat is so heavy and big we didn't get much sloshing done. But it worked! For about a year, then it started to leak again.

Then I started to research Sodium Silicate or water glass. This is mostly non-toxic and has been used to seal radiators, something on a nuclear submarine and most famously the Fukushima Daiichi Nuclear Power Plant. When heated or dried, this can form a silica gel which is no longer water soluble. It also is a coagulate with any particles in the water. This means that it can form little globs that help seal the leaks. I can't really heat my tank so I had to go with the temperature of the city water I was using (maybe 75 deg F).

There are some really cheap products out there that are sold for sealing hot tubs and pools which are sodium silicate and cellulose fibers dissolved in water. I made my own by dissolving a few sheets of marine toilet paper by shaking it up in a quart of water. Then kept adding sodium silicate until no more would dissolve.

This material doesn't easily mix with water, so I slowly added the quart as I completely filled the 200 gallon water tank. It almost instantly stopped all of the leaks!

I took about an inch off my water pickup so that there is some of the heavy solution is left in the bottom of the tank (because it really doesn't mix well). This is good because a professional tank repairman told me that most of the leaks occur between the tank and the supports, and at the joints. After about a year, there is still no indications of any leaks. One of the things that I found out is that sodium silicate is sometimes used to treat aluminum to prevent corrosion (bonus!!!), but I'm guessing that this will work with other tank materials as well.

None of the Material Safety Data Sheets that I could find indicated a toxic effect (no LD50). The concentrated solution had a pH of about 11 (a pH of 10 or above is considered potentially hazardous),but after mixing one quart with 200 gallons of city water, which was slightly acidic, the pH was only about 8.5 (7 is neutral). The water does leave a film on some glasses after being washed in it. And, the water was kind of slippery which made my pressure pump cycle for a second about every hour. But that went away in a couple of weeks. That's it for negatives that I could find. Please let me know if there are any others.

Anyway, this has worked and was really cheap. Hopefully, this will save someone the stress that I went through...
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Old 30-07-2018, 19:08   #2
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Location: Winthrop, MA
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Re: Leaking tank - water - aluminum - Morgan 49 - Sodium Silicate

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Old 30-07-2018, 19:15   #3
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Location: SW Florida
Boat: Morgan, Out Island, 49
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Re: Leaking tank - water - aluminum - Morgan 49 - Sodium Silicate

I almost forgot, heat might make the solution form solids inside the pipes. I don't use hot water so I am not able to report on this. Also, I haven't experienced any pipe, pump, or faucet plugging on my boat. Please let me know if you do. To be on the safe side, it might be a good idea to start off with a very dilute solution.
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aluminum, morgan, water

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