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Old 03-06-2011, 11:17   #1
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Fixing Plastic Freshwater Tank

Well, at least I have found the problem!!

One of my plastic water tanks has a 3 cm (1.5 inch) crack in it and its piddling water when its full.

I 'fixed' it a few months ago with a hard epoxy putty. However the instructions must have been wrong

What would you do to fix it 'properly'?

I am thinking a nice splatter of my silicon sealant. But knowing boats I thought I better ask....


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Old 03-06-2011, 11:21   #2
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Re: Fixing plastic freshwater tank

I don't know if anything will stick to those rotomolded plastic tanks.
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Old 03-06-2011, 11:34   #3
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Re: Fixing plastic freshwater tank

Your best bet would be to patch it rather than attempt to fill in the crack.

1. drain the tank.

2. Roughen up the area around the crack or tear and drill a small hole at each end of the crack as an arrestor.

3. cut a fiberglass material patch larger enough to cover the crack with a 5cm margin

4. coat the area around the crack liberally with epoxy so that the coated area is slightly larger than the patch.

5. Lay the patch in place and coat the patch and surrounding area with epoxy.

6. allow to cure and set before refilling the tank.
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Old 03-06-2011, 11:40   #4
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Re: Fixing plastic freshwater tank

It might be worth looking at this site as well for some more ideas:

Plastic welding, plastic welding tools, plastic welding equipment, kits, rods and supplies.
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Old 03-06-2011, 12:22   #5
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Re: Fixing plastic freshwater tank

Thanks Astrid,

That website is good, but you plan is much easier

Mark
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Old 03-06-2011, 12:57   #6
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Re: Fixing plastic freshwater tank

I have seen (and used) epoxy made specifically for bonds to plastic. Polyethylene, which what is I believe your tank is made of, is notoriously slippery and bonding to it is not easy. First determine what the material the tanks are made of *exactly*, then if they are polyethylene, try epoxy made specifically for polyethylene.

TAP H/LDPE plastic epoxy.


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Old 03-06-2011, 13:28   #7
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Re: Fixing plastic freshwater tank

The tank in my boat had a leak in it which I discovered when the water started tasting salty. The bottom of the tank is the layer in between the encapsulated keel area and the bilge. Well, wound up glassing the entire inside of the tank, well up the sides. It fixed the problem but was a PITA to do because access is through three 6" bronze screw out plates and the bottom is at a long arm's reach. I don't use the tanks for drinking so am not worried about chemicals dissolved in the water but using a drink-safe final coat is something to think about. I don't think you'll get anything to stick for long on polyethylene. Think I'd just try some 5200 and see what happens first unless you're going offshore. You can always glass over it later. Darned built-in tanks seem to be a constant weak point in a lot of boats. Also thought about tank liners before I started glassing.
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Old 03-06-2011, 13:31   #8
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Re: Fixing plastic freshwater tank

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Originally Posted by smurphny View Post
...I don't think you'll get anything to stick for long on polyethylene. Think I'd just try some 5200 and see what happens first unless you're going offshore. You can always glass over it later. Darned built-in tanks seem to be a constant weak point in a lot of boats. Also thought about tank liners before I started glassing.
The trick is preparing the surface correctly and use a compatible adhesive. No need to glass over the entire tank.
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Old 03-06-2011, 15:17   #9
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Re: Fixing plastic freshwater tank

There are a number of plastic formulations, of which polyethylene is just one...one that NOTHING will bond or seal permanently. Heat welding, which require melting the edges of the crack while simultaneously injecting new melted PE--creating a continous mass of PE-- is the ONLY thing that works. Depending up where the crack is located, the weight of the contents in a full tank will most likely pull the weld apart again.

The BEST solution--and most likely the least expensive too--is a new tank. Ronco Plastics (no relation to the Vegomatic Ronco) Ronco Plastics is your best source...they make TOP quality thick-walled rotomolded tanks for a very reasonable price and and have more than 400 shapes and sizes, over 100 of which are non-rectangular...and they install fittings in the sizes and locations specified by the customer when they make the tank. Their catalog is on their website...they're great people to work with.
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Old 03-06-2011, 15:44   #10
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Re: Fixing plastic freshwater tank

One thing good about the tanks in a 393, they're quite easy to remove. It might be worth your while to get a replacement, Mark.
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Old 03-06-2011, 16:18   #11
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Re: Fixing plastic freshwater tank

Why not cut a hole in the tank where the crack is and fit a round plastic tank access panel,the type they fit to clean out tanks ??
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Old 03-06-2011, 16:26   #12
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Re: Fixing plastic freshwater tank

Miles of HDPE pipe are maintained and repaired, and there are many people who repair HDPE Kayaks with holes in them. This is material science, not rocket science.
Plastic Kayak Repair
and
Repair of Whitewater Boats using Plastic Welding and other Techniques
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Old 03-06-2011, 16:45   #13
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Re: Fixing plastic freshwater tank

That's not a half bad idea, depending on the location of the crack. Where exactly is it?

Yes, PE pipe and kyaks are mended regularly, but neither have 8.33 lbs/gallons of material inside them trying to push the crack apart again.
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Old 03-06-2011, 16:46   #14
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Re: Fixing plastic freshwater tank

Quote:
Originally Posted by steamgoat View Post
Why not cut a hole in the tank where the crack is and fit a round plastic tank access panel,the type they fit to clean out tanks ??
My thought too, but we used to repair the soles of skis with the plastic stuff used to hold tins of beer together by melting with a candle and dripping it in a split. Presumably Mark has some beer and therefore the plastic stuff on board

However, why did it split? because unless you can hold it rigid that is now a weak spot if it flexes, hence the Steamgoats hatch idea.

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Old 03-06-2011, 17:30   #15
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Re: Fixing plastic freshwater tank

Google "Polyethylene water tank patch". There are plenty of sources to choose from.

I also found this...
http://www.mrstickys.com/products/PO...NUAL-MIX).html

I would rough it up with some 40 to 60 grit to get a better physical bond.
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