Sealing Stainless Steel Water Tanks

[BigART]

We had been getting rusty water from out stainless steel water tanks, so we have installed some inspection hatches and given them a scrub out. Unfortunately, during this process, we cleaned out the bit of rust that was sealing one of the seams and one promptly started leaking. I have found the leak and don't want to rip them out to replace them. What 'juice' would be suitable for sealing a small leak in a seam, Sikaflex 291, epoxy, some sort of tank paint? Any ideas?

 

[Allanrichard]

I have used Fernox very successfully on our tanks. Applied on the OUTSIDE of the leaks location it looks like a clear thick rubbery solution and cures on contact with water. Comes in a yellow tube from Homebase, B&Q, plumbers etc.

Our leaks have been ok for three seasons now after the application.

 

[Nauti Fox]

Brilliant tip Allan, ours is leaking somewhere and while I'm trying to get at the tank I've stuck a Vetus soft tank in. Was wondering what to try and seal our tank with and that sounds ideal(as long as I can get to the leak as I think they've built the boat round it).

 

[penultimate]

Would be very interested to hear of long term experiences of using Fernox to seal leaks. My 30 year old boat started developing leaks along the edge welds of the stainless steel water tank some 10 years ago, as did owners of similar vessels.
The welds crack, and then crevice corrosion sets in, I believe because of flexing of the panels. Some of the other owners resorted to an angle grinder to remove the tank completely and replace it with flexible. My solution, almost as drastic, was to cut access ports to enable me to glass in wood stiffeners to the sides and underneath of the tank. I then encapsulated the sides and bottom edges with glass mat and epoxy.

 

[Evadne]

Re: fernox

I'd forgotten about that stuff, we have an intermittent leak that I've tried lots of things on over the years, I should get some if it starts up again. The last stuff I put on was Marine mastic (or something like that), a white, non-setting mastic that comes from chandleries in a little tube with a big price tag. It seems to have been working for two years now, though.
re. Fernox, when I was renting a big house with some friends the (pre-war?) hot water cylinder in the basement started to leak, so the landlord kept slapping fernox onto it until it stopped. It looked like it had grown a big orange carbuncle, but eventually it worked. It must be cheap, he wouldn't have used it otherwise.

 

[PaulJ]

From the above replies it would seem that Fernox would be a good place to start because it is easy, though I have never used it myself. For what it's worth, I had a stubborn seepage from a mild steel diesel tank which defied several attempts to seal it. On the umpteenth attempt I have finally been successful by using a fairly runny epoxy (West system) with some fine chopped strand glass matting on the inside of the tank. It seems to have worked with diesel so I think it should also seal a water tank. Whatever you do, I think the final result will depend on extremely thorough cleaning and also abrasion to give the sealant something to key to.

Paul

 

[WayneS]

As others have mentioned, Fernox should do the trick. Even though the instructions say that it can be used on wet surfaces, my experience is that it rarely works unless the surfaces are dry before application. Once it is semi dried you can apply water to it to speed up the curing.

If you can get to the leaking area easily, why not try re braising the weld. This can be done with an off-the-shelf blow torch and pre fluxed braising rods from your local hardware. That's what I did when I was adding some more outlets to my tank.

W

 

[alahol2]

I have a stainless diesel tank with a breather pipe. The weld/braze/solder (?) joint had cracked. I flooded the area with ordinary solder using a small gas blowtorch. The joint is now as good as new again. I didn't think it was possible to solder stainless but this seemed to work OK. It may be a solution. Does anybody know if it is possible to solder stainless?

 

[VicMallows]

When I fitted new stainless tanks, I tested them first and found a very small leak on one seam. Rather than cart it back to the manufacturer, I injected a tiny bit of epoxy glue and it's been fine for 15 years.

Vic