Fixing tank Leaks

[SydneyTim]

My boat has integral fibreglass tanks which have begun to leak slightly. Access to them is straightforward and I am wondering if I can just "paint" the inside with some wonder product and fix the leaks. I need to fix both diesel and water tanks so something that won't dissolve with diesel and won't kill us in the water would be great.

I am thinking some sort of epoxy approach would work, but know very little about epoxy other than the two part glue being excellent.

Any advice gratefully received

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[HeadMistress]

By the time a fiberglass tank has leaked enough to be noticed on the outside, it's likely that the tank walls around the leak(s) have been soaking up water or diesel from the inside for quite a while...which means you prob'ly have some fiberglass repair work to do before applying any coating to seal the inside of the tanks. It's especially important that any repair work be done in integral tanks if any tank wall is structural.

<hr width=100% size=1>Peggie Hall
Specializing in marine sanitation since 1987

 

[jerryat]

Hi,
I agree with headmistress and suspect your tanks are well past their sell-by date.

Why not consider fitting either a standard or a purpose made flexible tank inside the existing ones? Difficult to judge without seeing the actual situation, but compared with the likely work necessary to bring your tanks back to a usable state, that's the route I'd go. As you are probably aware, flexi tanks are readily available for both water and diesel so there shouldn't be a problem with supply.

Fitting them in a space that restricts movement and therefore the risk of chafe, i.e. inside the existing tank, is an ideal solution.

Hope this helps,

Good sailing!

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[SydneyTim]

Thanks for the advice, I'll give a bit more detail on the situation to see if that changes anything.

My main diesel tank is at the moment not leaking, but the second diesel tank was decommissioned a few years ago by a previous owner because it was hence my concern. The two water tanks both leak at the bottom joint.

The tanks have been constructed by glassing 3 walls and a lid to the hull, ie use the hull as one wall of the tank. The leaks are through the joints between the tank wall and the hull, and do not appear to have damaged the integrity of the walls in any way. I guess I am wondering if I reglass teh joints on the inside and seal the whole lot of with some sort of epoxy based product whether that will solve the problem.

On the subject of flexible tanks inside existing, how do the fittings get set up as all the flexible ones I have seen have big plastic fittings on the sides/top. Given the need to expand and collapse and I don't see how I can avoid it "hanging" by the fittings when it empties and putting pressure on them when full?

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[jerryat]

Hi!

As I said earlier, it's almost impossible to give a definitive answer without knowing the precise shape/size of the tanks, but as the flexible units are used as standard equipment on many new boats, as well as replacements in situations such as yours, the concerns you indicate over connections must have been well considered by now. I would suggest contacting one or more of the main suppliers, giving them as much info as you can, and getting a consensus as to whether this might be the way forward. They are sure to have come across similar situations before and will be able to advise you.

The GRP repair option, as you explain it, dosen't sound to difficult, and may prove the easier (and certainly cheaper) way in the end. Personally, I wouldn't fancy having the hull forming one side of the tank, especially if the same applies to the water tanks (osmosis) but if it's been successful in the past, why not?

Sorry I can't be more helpful, but it's difficult to envisage your existing tanks.

Hope it all turns out well for you.



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[oldsaltoz]

G'day Tim,

Given your description and the fact that access is good, I would consider repairing the existing tank if I were in your position. However, just laying up some glass over the existing leaks might not be a good idea.

This type of failure sounds like poor preparation when first built, but could be due to flexing over an extended period, either way, covering it will not cure it in the long term. More importantly, you need to establish that the hull has not suffered.

So, I think you need to do 2 things; replace the bond between hull and tank walls, and, make sure the hull integrity is good.

The only way I can see to do this is to start by removing the existing hull to wall joints, but it may not be necessary to remove them all, as the upper area of the tank will have had a lot less exposure to the contents and to flexing.

Put a big fan in the companionway and open up the hatches, this will carry a lot of the dust out, and wear a good quality respirator, ear muffs and goggles.
Starting at the bottom, grind (or chisel if you want less dust) the wall only at an angle so that when you penetrate the tank, the hull still has a little of the original join on it, the wall should be ground to produce a feathered edge at least 50 mm wide and down to nothing at the joint, this will leave a small gap to enable you to remove the last of the joint that remains on the hull. This section should be ground down with great care to ensure you only remove joint material and perhaps a mm to ensure you have a good clean base for a bond.

Grind or chisel the remaining sides to the same feathered edge, but only go as high as you need to; you will see a brownish stain in the areas that were leaking, keep going up till you are above the known leak points, and then keep going till you see no more staining.

Now do the same on the second tank, this will save you a second clean up inside the boat, as this is the only real dusty work.

Time to do the repair work; get some plastic sheeting and tape it to hull below the area to be repaired, also put some in all the areas you will be walking, including the cockpit, this will save a lot of cleaning later.

Now have a close look inside the tank, look for patches of discoloration and run your fingers over it checking for any sign of blisters or voids. If you find any, continue grinding and remove the tank wall to give you access to repair the hull.

Assuming the hull is in good condition (I suspect it will be) use an 80 grit sandpaper and clean the inside of the tank walls and hull, taking care to establish a good key in the joint areas, at least 30 mm wide on walls and hull.

Clean the inside of the tank with Acetone and white cotton rags, drop some rags in the bottom to soak up any run off, then remove them to finish cleaning the bottom section, but have more rags outside under the tank to collect the run off. put the rags outside and downwind as soon as you can. All the time making sure the area is well ventilated, the fan in the companionway should be pushing air in, not extracting it, as the fumes are highly flammable.

Now run some wide masking tape over the join area, make sure none of it protrudes into the tank; you are now ready to mix some Micro Fibres and Epoxy resin to provide a backing for the fibreglass. Mix your resin first, then add the fibres, you are looking for a consistency a little thicker than toothpaste. Do one side join then the other then the bottom, apply the mix and run the back of a spoon over it to give you a rounded corner, this will add strength and make it easy to clean later. Let this cure overnight and the next day (or weekend)...

Regrind the feathered edge to remove any high spots left by the fibre mix and clean the area with acetone fill any low areas so you end up with a near flat area, mix some more Micro fibres and lay in another rounded corner, but keep it small; this is to avoid sharp bends in the new lay-up of fibreglass and will still be going off when you apply the first bit of glass, so only lay the fibres over an area you plan to complete in the next hour or two.

Next you need to cut the fibreglass to the required length and width prior to mixing any resin. Using a 250 gram mat work on placing 5 to 7 layers one over the next, wet on wet. each strip should be smaller the one it covers for the first 3 lays, then another strip to cover all and work down in size again till the required thickness is reached. So, we need to cut the first strip the full length of one side plus 60 mm and at least 120 mm wide, this will cover the 50 mm feathered edge and the rest will go over the fillet and hull; reduce the next strip by 25 mm all round (about 70 mm wide) the next about 30 mm, then another the same as the first and so on.

Laying up strips can be a bit messy, so I would suggest you wet them out on a board covered in plastic or some other non porous material. using a small ridged steel or alloy roller, roll out as much resin as you can without overworking the fibres. Epoxy resin and mat should be around a 1 to 1 ration, the old wax resins can be up to 4 resin to 1 mat. the closer you get to a 1 to 1 ratio with epoxy the stronger it is. Just make sure the mat you use is designed for epoxy resins, not chopped strand as it holds too much resin and will be a weak joint.

When all the fibreglassing is finished, give it a good sanding to remove any high spots and then a couple of coats of resin to seal it. Note: all resins will suffer from exposure to UV, so it will require a coat of paint when finished.

The inside of the tank can be coated with a suitable flow coat, a phone call to your local fibreglass outlet will give you the advice on what type to use for each tank.

Some pointers.
Only mix resin in shallow containers, or it will heat up very fast and go off.

Acetone will clean all tools and minor spills, drops etc, but you can use white vintager to remove the bulk, saving Acetone and the chemical exposure as well
as a few bucks.

If resin does cure on your roller, and blocks the grooves, just heat it with a gas flame and it will burn off, a wire brushing and she's as good as new.

Latex rubber gloves like a surgeon uses are only a few dollars for 100 pr, and will save you skin and a lot of soap.

One litre Ice cream containers are good for mixing resin in, and easy to clean when the resin has cured, also handy half filled with vinegar for primary cleaning, just drop your bits in and let them soak; so start collecting.

Only use lint free rags, cotton is fine, we don't need contaminated materials.

As soon a mix of resin shows any sign of going off (thickening) discard it, or you will have a sub standard lay-up.

And last but not least, fibreglassing is not that hard to master, if you are unsure, have a little practice first, you will be surprised how easy it really is. there are a multitude of books and articles on the net you can study, all good stuff, have a look at the west epoxy site, lots of good stuff there for the rank armature and the pro.

I hope this helps

Avagoodweekend.



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