How to fix a leaking GRP water tank?

[rjcoles]

Over the last season I noticed that the bilge was getting increasingly full and would emptying every couple of days. I suspected a leaking stern fitting as my rope cutter had done its job a couple of time last year.
Now the boat is out of the water the stern fitting looks good and tight so the problem is elsewhere. Whilst living onboard last week I filled the water tank (1000l) and low and behold water in the bilge next day! This was pumped out but the bilge was again wet the day after, this tends to show that the problem is not with the filler tube or overflow as both enter the top of the tank. The problem must be in the GRP Tank itself.
This tank is fitted on top of the encapsulated lead keel and below the cabin sole and to remove it will mean demolishing the cabin furniture and that’s a no no!
Is there any product that can be used to seal a portable water tank from the inside ( like Radweald for cars) or any other suggestions on how to fix this leak?

 

[coopec]

I've fabricated all my water tanks in fiberglass and painted them inside with a "water based bitumen" to make them suitable for potable water. It is quite a thick product so it would probably seal the leak if it was not a gaping hole but a crack.

https://2ecffd01e1ab3e9383f0-07db7b...duct/92f5ef53-898e-4b26-8ee8-d0ffeee1a196.pdf

But why did it develop a leak? Are they fairly lightly constructed? Can they move a little and have worn?

I just hope mine aren't too light. But they are removable so I could beef them up a bit if necessary.

View attachment 70652

 

[Tranona]

Empty it completely and try and locate the leak which you may be able to repair using conventional GRP repair techniques. However you may not find this easy because of limited access and baffles inside. What you are experiencing is the main reason why such tank installations are no longer used. Seemed a good idea at the time, but long term perhaps not so good. Not aware of any magic potion you can just pour in.

Unless you can identify where the breakdown is and repair it through the inspection hatches you are probably going to have to bite the bullet and remove it. Remember an article in PBO about exactly this issue and the solution was to cut the old tank out in pieces and replace it with smaller (3 from memory) tanks. This avoided cutting all the furniture out, but obviously resulted in a reduction in capacity.

You don't say whether it is a separate tank or part of the hull moulding as this will influence how you deal with it if you do go down the replacement route. For example it may be possible to cut out part of the top, remove the baffles and install a flexible tank made to the shape of the remaining cavity.

 

[Nigelb]

I had a very similar dilemma last season, after much research I decided to cut the tops off and install two new TekTanks.

 

[Tranona]

Good solution. Well done.

 

[coopec]

When I built my water tanks I followed Steve Dashew's Circumnavigator's Handbook advice that small tanks were easier to secure than one large one, water usage was easier to monitor using a number of tanks, water obtained from a dubious supply could be kept separate and finally, tanks had to be removable for cleaning and maintenance. That is why I went for a number of small tanks. But each to his own.......

When I phoned Nuplex Resins and told the technical guy there that I intended to use the boat hull as part of the tank he said NO! and told me to contact a paint or coating supplier to get expert advice. I was told I couldn't use resins as I couldn't control the cure and therefore chemicals could leach into the water

Quote " We would recommend an Isophthalic resin for potable water: Crystic 491pa has been used for this but the essential point is to post cure the tank to ensure the residual styrene content in the laminate is at extremely low levels. The recommended schedule is 24hrs at room temperature followed by 5 hrs at 80°C. Fill the tank up with hot water (60°C-80°C) containing a non perfumed detergent, leave to stand for 2 hours and empty. The tank should be filled with clean hot water several times before use

Just now, while I was doing some research on the subject I came across one of Steve's books (Practical Seamanship) which has been published on line: I think it is a tremendous resource. Others may be interested in having a read.

https://www.setsail.com/PracticalSeamanship.pdf

 

[rjcoles]

Thanks for the advice, I would of replied earlier but got caught up in Steve Dashews book!
I think I may be able to cut another access panel in the top of the tank the other side of the baffle so that I may be able to spray or roller some substance(?) on the walls and floor of the tank. The tank is too big (750l) to remove and replace without a seasons work and SWMBO will not like that. It will be impossible to get to all areas to abrade the surfaces unless I can use a grit blaster and then hoover out and then paint with epoxy or other suitable substance. What would you use?

 

[coopec]

After being told I must not store drinking water in a fiberglass (or epoxy) tank I went to a technical advisor at a paint/coating firm and told him I wanted paint my water tanks in the hull of my yacht. He said they had suitable products but he was worried about their cure. How much sun will it get on it? I decided I had to do my own thing.

After some research I settled on

CROMMELINS
Water Based
Bitumen Paint
Heavy duty, flexible , below ground waterproofing membrane.

View attachment 70722

Another product I could have used was


Product Guide - Bondall
www.bondall.com/wp-content/uploads/Bondall_ProdGuide_141104_Web.pdf

Concrete floors. • Waterproofing admix. • Renders above/below ground level. • Potable drinking water. • Forms a permanent waterproofing barrier. • Waterproofs cement repair putty. • Can be used on above or below ground applications. • Can be used on interior or exterior applications. CONCRETE ADDITIVES. FEATURES.


Apparently Crommelin's Product and Bondall's product are Australian but there must be UK equivalents?

Everbuild 90101 Bitumen Paint 1L - Black: Amazon.co.uk: DIY & Tools
https://www.amazon.co.uk/Everbuild-90101-Bitumen-Paint-1L/dp/B0012PLK4W

Rating: 4.7 - ‎67 reviews
This product has a fast drying time and is suitable for use with portable drinking water tanks. Everbuild EVB90101 Black Bitumen Paint is a solvent based, full bodied black bitumen paint. When dry, the product forms an odourless and taint free bitumen film suitable for the protection of metals, concrete roofing, felt, fibre, ...



Fibreglass Water Tanks
Fibreglass tanks need a food-grade coating to be up to Australian standards for storing water.

Styrene Exposure & Monitoring | Safe Environments
www.safeenvironments.com.au/styrene/
Styrene exposure is an irritant which may affect eyes, mucous membranes and have gastrointestinal effects. Long term health effects may affect the central nervous system which may include symptoms of nausea, fatigue and depression.

Clive Cooper

 

[Tranona]

Thanks for the advice, I would of replied earlier but got caught up in Steve Dashews book!
I think I may be able to cut another access panel in the top of the tank the other side of the baffle so that I may be able to spray or roller some substance(?) on the walls and floor of the tank. The tank is too big (750l) to remove and replace without a seasons work and SWMBO will not like that. It will be impossible to get to all areas to abrade the surfaces unless I can use a grit blaster and then hoover out and then paint with epoxy or other suitable substance. What would you use?

If water is getting outside the tank it means there is a crack right through the laminate so randomly pouring in something sticky is unlikely to seal it. You really need to identify where the failure is and then take a view as to how best to repair it if you can in situ.

 

[rogerthebodger]

Clive

It is in my view better if the inside of water tanks are white as this allows you to see and muck that accumulated in the bottom with the black bitumen its not that easy.

I also paint the bilge of my boats white for the same reason.

 

[coopec]

Roger

They use the water based bitumen to line fiberglass tanks, pipes etc and the fact that the product is black is a plus as it stops algae growth. (Algae needs light) But of course that does not matter in a boat.

If you can find a food grade lining that is white that would be good: perhaps there is such a thing? (If I find time tonight I'll do some searching).

One of the requirements that Steve Dashew had for water tanks on a boat was that they should not be more than arms length deep as you would not be able to clean them otherwise. (He also said they should be removable for maintenance and cleaning)

All my tanks have large lids that can be removed without moving the tank. If I had a torch I would easily be able to see if there was any crud at the bottom

View attachment 70729

You say "I also paint the bilge of my boats white for the same reason".

I also paint my bilges white too with "Killrust" or "Rustguard" although my boat is fiberglass. (My yacht has a long keel with internal ballast so I am putting lids on each section to stop rubbish falling into the bilges.)

Clive

 

[rogerthebodger]

On my steel boat I have stainless steel water tanks and the hatch is of such a size I can get my head and shoulder through.

I made a fabricated GRP waste tank as stainless would not last long.

This is my initial fabrication using flat GRP sheets. From this I layed up several layers of GRP on finished inside with ceramic flow coat.

The paint I am looking for is for a Ferro boat that has water tanks built into the hull and do not have easy access,

 

[coopec]

Roger

There are food grade paints but would they "cure" properly inside a boat and would they stand continual immersion in water? When I made up my waste tank.....Maybe I'll leave that for another thread.

Clive

 

[rogerthebodger]

Roger

There are food grade paints but would they "cure" properly inside a boat and would they stand continual immersion in water? When I made up my waste tank.....Maybe I'll leave that for another thread.

Clive

The closest I have found is fish pond paint but is is not normally white if either blue or clear.

 

[coopec]

Roger

I didn't realize I could have got "sandstone" color. That would be alright?
http://www.crommelin.com.au/range/at-home/waterproofing-products/pond-sealer-colours/

Features & Benefits
Remains permanently elastic to accommodate structural movements
Non-toxic and safe for fish and plants
Suitable for use in collecting or storing drinking water
Safe and easy to apply
Excellent adhesion to substrates
Quick drying
Good crack bridging properties
Easy to repair




Clive

 

[rogerthebodger]

Your lucky out equivalent is only available in black and blue.

https://www.duram.co.za/product/durapond-2/

 

[coopec]

If you worry about drinking water from "industrial type" tanks not meant for potable water this thread could be interesting and informative.

http://forum.woodenboat.com/showthread.php?108058-Food-Grade-Epoxy-for-Water-Tanks

https://www.cruisingworld.com/how/marine-systems-potable-water

https://www.passagemaker.com/technical/potable-water-systems


Apparently Crommelins have agent for their products in South Africa and the UK
http://www.crommelin.com.au/stockists/International-Stockists

 

[coopec]

Your lucky out equivalent is only available in black and blue.

https://www.duram.co.za/product/durapond-2/

I wondered why you said that but the penny dropped: you are in Durban.:sleeping:

(I can't find any color other than the Dalven Black)

 

[coopec]

This 44ft yacht obviously has 8 water tanks. (Looking at "Related images" other yachts have multiple tanks too)

View attachment 70752

 

[paulajayne]

Try putting some food dye into the tank - should help to trace where it is leaking from.