steel water tank paint

[Crazy Goose]

Hi,

I would like some advice on paint systems for water tanks. The water tanks are part of the steel hull (except for the cover which is part of the wooden floor, and hermetically sealed). In some areas the old paint was flaky. All this has been scraped off and lightly sanded. Most of the bottom coat is firmly attached but several areas require rust treatment (for this I would use Ospho). Question : what coating/paints would you suggest after that?

Thanks,
Phil

[MikeJohns]

Hard to give advice without knowing what your access is like and what sort of rust we are talking about. A photo would help.

Phosphoric acid is a poor way of treating rust and is pretty useless long term.
It is effective only on the top layer of the rust and I'd much rather see you grind and power wire brush the steel. Even a grinding burr on an electric drill or air grinder can be pushed into the pits and clean things up a lot.
What you must do is get rid of the rust, so if you have black areas after grinding, knock them with a centrew punch untill all the scale is loose then wire brush ( even a wire brush in a drill is good) and then epoxy 2 or more coats.

We usually follow up with a potable mastic high build paint which is often made for coating the inside of water pipes it is cheap goes on very thick and does a great job and is easily re-coated.

If the coating is good you don't need anodes in the tank.

Hope this helps
Cheers

[Submarine Tom]

I have no experience with this topic but it would seem glass beading might

be a way to go here to clean and surface treat this tank prior to re-

painting.

Tom

[Crazy Goose]

MikeJohns, thank you for the info.
The rust is rather superficial and I indeed planned on putting the phosphoric acid on only after having brushed almost everything off. Just to make sure to get at the last little bits and get a really deep cleaning.
I have good access since I removed the tops of all the tanks.
I'll try to post a photo in the coming days (have to get to the yard).
Phil

[gonzo]

There is a tank epoxy specifically for that use.

[Frosty]

Surface tolerant Jotamastic 87,---made by Jotun.

As a steel boat owner you should get to know Jotamastic and coat tar epoxy.

[MikeJohns]

Frosty
Coal tar epoxies have been banned in many places and It doesn't count as a potable water tank coating, that's why we use the other mastics.

There are some good surface tolerant epoxies, one we use can be applied 3mm thick per application. A mastic overcoat protects any cracks that may develop in the coating.

Hempel Hempadur 35560 is a solvent free, polyamine cured Epoxy, certified for potable water. That is a international standard tank coating used by the industry.
data sheet
Jotuns Tankguard Zinc is another choice, certified too!

Do NOT use Jotamastic! That is good for decks and cargo holds. DO NOT use ep tar as Mike already mentioned!
Sorry Frosty


Regards
Richard

[Frosty]

No, I agree the coal tar would leave a taste, I did'nt know it was banned but coal tar epoxy is a good bond to steel and is very useful on the hull.

I have used Jotomastic 87 silver on a water tank, it even had a hole in it but the paint is so think it virtually gives it a liner.

[Crazy Goose]

Guys,
thank you for the different product names and discussion.
I also looked into Protectakote, a polyurethane paint. But it might end up being a very costly choice.
I am going to the yard tomorrow and will post a photo shortly.
Phil

[Crazy Goose]

Hi, here some pictures about access to the watertanks and the condition.

[Crazy Goose]

OK, I've tried to add the pictures but they exceed the filesize limit. Have to find a way to reduce their size before trying again.

[Frosty]

Well, just post one pic per post.

[Brent Swain]

Big ships use cement wash . If you have ever tried to get hardened cement off a rusty shovel , you will know how it sticks like **** to a blanket. Being slightly alkali, it is a rust inhibitor. Keeping a bit of water in the tank keeps it wet and thus aids curing of the cement.