GRP water tanks - How to repair gelcoat damage found

[Bilge Rat]

Wife of Bilge Rat here....

We have a GRP water tank moulded into the floor of the saloon, having noted some distinctly "eggy" smells coming from the taps we investigated and what we found when we took of the inspection hatch has driven us onto bottled water for drinking. We have to sort it out but would appreciate some good advice on the best way forward.

The tank is gelcoated and a baffle situated near the top of the tank has clearly been damaged and lost some of the protective gelcoat. There is an area of fibreglass exposed (I seem to think that this may give off some noxious substance) so now I have worried myself.

The smells may have been more down to water stood in the pipes for 2 weeks but we also found a large qty of "crud" at the bottom of the tank together with some slime on the top of the tank so everything needs a thorough cleaning this winter and of course the repair to the gelcoat.

Initial thoughts are to dry the tank thoroughly in October and repair the gelcoat prior to relaunch next spring but there are so many questions in my head.

1. Will saturated glass fibre really dry out without heating in a few month?
2. Will I make the situation worse if I repair before dry and trap in water?
3. Do I need to consider a liner?

We need to get this right as we will be cruising for a few months next year and I want to be able to confidently drink the tank water without fear of disease or poisoning.

Thanks Jackie

 

[Geoff Enigma]

I had a similar problem with sulphurous smells coming from the taps when I got my boat which had been standing for some time. I first thought it was the tank but that was clean and smelt sweet I put various cleaning things through the system (Milton etc) which improved things a bit but after the water was not used for a week or so a slight smell would return. Finally I decided to fit a pressurised system and replace the pipe work as I was not sure of its age. Although most of it looked ok some pieces that were in the bilge out of sight were a strange green / blue colour but after replacing the pipe work the smells have gone. I can only assume that there was some sort of nasty living in the pipes or possibly something leeching through from the liquid in the bilge.
I realise that this is different from your question but could be a contributing factor to the smell also in my case could be partially due to the increased amount of water passing through the system.

 

[Bilge Rat]

Cheers Geoff,

I think you are right and that maybe there are a number of factors at work here. We have replaced some of the water pipes since buying the boat 2 years ago but I suspect there are some inaccessible ones that we and previous owners have avoided due to it being in the "too difficult category"

We're at the boat this weekend, making good use of the last of the summer so I'll take another look at the pipe runs.

 

[vyv_cox]

How big is the damage to the internal epoxy? If it is not too big I would repair with one of the epoxy putties that can be used underwater, in which case it is not necessary to fully dry the glassfibre. My own preference is Milliput, far cheaper than buying the equivalent from marine or plumbing suppliers.

If it is a bigger area I assume that there are gelcoats or resins that can accept wetness, so try asking one of the suppliers.

I agree the comments above. We scrub our water tank every few years but an unpleasant taste persisted until we changed out all the hoses, despite dosing with Milton and stronger bleach.

 

[oldsaltoz]

Wife of Bilge Rat here....

Initial thoughts are to dry the tank thoroughly in October and repair the gelcoat prior to relaunch next spring but there are so many questions in my head.

1. Will saturated glass fibre really dry out without heating in a few month?

Good local ventilation will help. I have seen solar fans placed in popes that run external air directly to area that needs drying, then there is the heat gun treatment over a few days. Only a moisture meter will tell you the truth.

2. Will I make the situation worse if I repair before dry and trap in water?

Most certainly, repairing it with ANY moisture means trapping the moisture and guaranteeing more problems later on, don't even think about it.

3. Do I need to consider a liner?

I would do a good repair job and not have to worry about a liner leaking or he problems they create with condensation.

We need to get this right as we will be cruising for a few months next year and I want to be able to confidently drink the tank water without fear of disease or poisoning.

Thanks Jackie

Given the limited information, I would look at getting the tank dry first, then sand the inside and wipe clean with Acetone and white cotton rags.
Then apply 3 coats of epoxy resin wet on tacky with a good air flow at all times (a fan running over the gob between applications)

Gelcoat is by no means fully waterproof or chemical free, an epoxy is a hell of lot more waterproof and harmless when cured.

The only drawback with epoxy is that it will degrade in UV light, but I suspect it will not see muck inside a closed tank below deck.

Good luck and fair winds.

 

[rob2]

+1

I would be inclined to empty the tank immediately to give it a head start in drying out. If at all practicable, I'd remove the inspection hatch whilst the boat is not in use to help air it, too. I don't know whether particular resins are better suited to potable water use, but epoxy is more water resistant than polyester resin.

My tank is GRP and has a clear perspex lid (underneath a benchseat, so no light issues. Happily it has always remained clean. The routing of the pipes to the sink is much longer than you'd first expect so as to negotiate stringers, etc. and at first, after a break, we'd get lumps of gunge coming from the tap! Tried Miltons, but it just isn't effective in the pipework once infested. Replace all the pipes in one go, including those to the "vanity" basin which has never been used, just to ensure there are no infested dead legs to stat the process off again. Taps, hose joiners, etc all got scrubbed through in bleach solution as well. I suspect the bug grew in the section of pipe that runs rather close to the engine, so presumably got warmer than the rest...

Rob.

 

[captainboo]

Epoxy Painting Watertank

I painted the inside of my grp water tank with a solvent free epoxy, primarily designed for floor coating but also used for tank lining. It is safe to use in contact with potable water.

I have three sections to the tank, each with an acess hatch about 8" across. I could just about reach the edges of the tank lying down with my arm in almost to my shoulder.

So I could see what I was doing I bought a cheap usb camera with leds from ebay and then used a laptop as a monitor. The setup worked reasonably well but I don't think I'll try keyhole surgery just yet!

 

[testmonkey]

Wife of Bilge Rat here....
...
We need to get this right as we will be cruising for a few months next year and I want to be able to confidently drink the tank water without fear of disease or poisoning.

Thanks Jackie

Well if you really want to be on the safe side, the right thing to do would be to install a flexible water tank (or two) inside your current tank.

Read this from West Systems and decide for yourself...

http://www.westsystem.com/ss/wood-epoxy-composite-tank-guidelines/
Considerations for potable water tanks
We have adopted the broad policy of not recommending epoxy for drinking water tanks because of regulatory and safety issues. The potential problems outweigh the benefits. To date, none of Gougeon Brothers' epoxies meet FDA regulations or any other drinking water certified approval. The major long-term concern with any plastic water tank is extractives leaching out in the water. Off-ratio, poorly cured epoxy can release extractives, as noted above. In the fabrication of water tanks and food handling equipment, the successful use of epoxy requires thorough mixing and adequate elevated temperature post-cure to assure the maximum cross-linking and cure of the polymer. These process controls are not always possible with the home-built tank. Unfortunately, neither Gougeon Brothers, Inc. nor any certification agency can verify the level of quality control exercised in the fabrication of the tank.