water tanks

[zeehond]

I opened up the water tanks on my steel yacht and have found some rust. What is the best way of treating this and what is a suitable paint to recoat the steel once the rust has been dealt with? All advice will be appreciated.

 

[tugboat]

In that environment, unless you can get rid of every trace of rust, you're going to get it returning whatever paint you use. The best coating is what we used in the MN. Get a bag of ordinary Portland cement and mix up a slurry in a bucket and paint it on with a big longhaired brush. This kind of coating can produce flakes from time to time so, given that our water pipes are somewhat smaller bore than merchant ships use, I'd suggest a filter close to the tank outlet.

 

[Ships_Cat]

You say some rust - if only minor patches and assuming the intention is to paint then just grind them off as preparation. In our own tanks which have only just needed minor attention after 10 years I was able to do that with a Dremel. If it is more than some rust then the ideal, if the equipmet can be got in is to sand/grit blast them clean - for that use an operator and many (here anyway) have small guns of the type used for small components etc that will get into small spaces.

For paint, the only sensible choice is to go with a good epoxy paint that is certified for use in water tanks. But if the existing coatings in the tank are not two pot epoxy then you will have to blast the tanks clean back to steel. In other threads on this subject peeps have said that it is not possible to do this and that it is too messy, etc, etc and moan, moan. I can assure you it can be done providing the hatches into the tank are big enough. If the tanks are already painted the chances are they have been blasted when new. Our own tanks were blasted when the boat was built and that was done through the inspection hatches - the tanks are only around 200 - 350mm deep, depending on where measured, as they are built into the bottom of the boat under the sole.

A good manufacturer of specialist epoxies for industrial and food industry use will make a recommendation suitable for potable water tanks (I don't think the likes of International or Jotun do them) - I cannot make a recommendation for you as I am in New Zealand, but here Altex Coatings are a respected supplier of such paints but they only operate here and in Australia. A google will find them and you may care to look at their site to get ideas of the different paint types available so that you are better armed to make your own enquiries..

You may find that there are two or three recomendations as certification of the paint or the recommendation may be limited by the tank capacity. For example a paint may be suitable for large tanks with alot of water per surface area of the painted surface but not for smaller tanks. But that same paint may be suitable for spot repair in smaller tanks if you see what I mean. Similalrly there may be a reommendation of a paint suitable for all tank sizes.

Often (but not here in NZ) you can only get these paints in minimum quantities of maybe as much as 4 litres but the cost is small compared to the effort of the whole job and the life from them. However, you will only need one type of paint ie don't need seperate coats of primer and undercoat as the epoxy paint which may be described as a primer/undercoat or just as an undercoat will go straight onto the steel.

If you have a nice boat which you and others would be proud of then avoid old fashioned recipes such as cement, etc. You will end up with problems you cannot see and ultimately with a disaster and plate chopping out episodes. Once epoxied check the tanks once a year until you get an idea of how often minor repairs are needed.

John

 

[zeehond]

Thanks for the help! I was hoping somebody might know of a UK product and supplier of a suitable paint system so I'll keep on asking!

 

[Ships_Cat]

A brief google came up with a number. Not being in the UK I could not comment on them but Leighs looked interesting.

Have you looked at the British Coatings Federation internet site at http://www.coatings.org.uk they have links to a whole pile of paint manufacturers? They also have a product finder - go to that and look under "Tanks" and give the companies that come up a call. I have invariably found the paint manufacturers extremely helpful in a number of countries even when they know they are only going to sell a few litres of paint for the application - I assume that would be so in the UK as well.

Have you tried phoning the engineers in some food processing plant or abbatoir to see what manufacturer they use for food grade coatings? Or a yard that builds or maintains steel vessels, for example?

John