GRP Water Tank Repair

[Sfalkner]

I would be grateful for any advice. The GRP water tank on my 1974 long-keeled boat was cracked and leaking into the bilge. The tank is a GRP moulding conforming to the shape of the keel situated under the saloon sole. There are two small round inspection hatches. I cut a circa 12” square hole in the top of the tank to allow access to work and used fibreglass tape and epoxy resin to repair the crack. I then replaced the “hatch”, this time using polyester resin as I had no epoxy available (the boat is in Greece). The crack repair appears to have worked but now there is a very strong smell and the water is contaminated by a strong taste of resin. I am not sure if it is the epoxy or the polyester. I am now back in the UK and cannot therefore do a “sniff test” to identify if it is the polyester or epoxy that is the cause. If it turns out to be the polyester resin then I will remove “the hatch”, grind all the polyester resin away and replace using epoxy or even fitting a proper inspection hatch. If it turns out to be the epoxy resin then I think the only solution is to open the “hatch” again, paint the inside of the tank to form a barrier between the epoxy and the water or, if that fails, have a bladder type tank made to fit the inside of the GRP tank.

I realise now that anyway I should have made the repair using “food grade” epoxy resin. Mea culpa, but I would value any thoughts on the type of paint I should use. I have seen some threads advocating a solvent-free bitumen paint as used in fish tanks. Would a water filter help? Any other thoughts would be very well received.
Thanks in advance.

 

[Trident]

You can coat either repair with epoxy aquarium paint (food grade but half the price) as epoxy will cover over polyester. If it is polyester however the smell and taste will fade with a few water changes. If you put a charcoal in line filter on the output of the tank this will actually remove the leached chemicals and makes it safe to drink again. I had to do the same 5 years ago and the full repair was polyester as it involved the keel tank with built in baffles etc and limited access. The smell only lasted through a couple of water changes (400L tank though) and the water from the taps having gone through the charcoal never smelt and tasted (and still does) fine.

 

[geem]

You can buy a WRAS approved two pack polyurethane paint specifically designed to coat the inside of drinking water tanks. No harmful chemicals will leach out. We coated our 800 litre grp tank a couple of years ago. It's like having a new tank. There is a company in Yorkshire that sell it. A Google search should find it

 

[Sfalkner]

Many thanks to Trident and Geem. Very helpful and I will look into both, as well as filters.