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Charlotte Grace

BRAND NEW WATER TANK COATING

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Hiya, first post :

 

 i have trawled, oh believe me i have trawled, to find the best way to coat an integral steel water tank for the first time. I was thinking Vactan might be a good shout for any any surface rust (the tank was built about 3 weeks ago) to begin and then blacking over the top. 

 

I figured why not about the coat of vactan first, can do no harm, but then the very kind Andrew at Vactan told me that he can't be sure how well Vactan will bond to new metal as its made, obviously, for rusty metal. 

 

So now I'm confused / concerned, and amongst all the water tank posts out in the ether i cannot actually find a post about a brand new tank?! I saw somewhere to just use blacking straight up, but I'm up for doing this whole vactan thing if i can save hassle in the future. 

 

Can you help?

to clarify i need answers to :

 

a) can/should i do a  vactan coating first?

b) which POTABLE water tank paint would you suggest go over the vactan, or

c) do i even need it post-vactan on new steel? some people even on rusty tanks say they only used vactan and this is new, but i dont want a situ where i used a vactan that didnt bond well to new metal and no blacking and then its all worse.

 

Ta 

 

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Paging @Dr Bob - There'll be a muppet along here shortly. 

 

Don't worry he's a very clever muppet and is our resident / in-house paint expert, I saw him a moment ago so we may have just caught him before his afternoon nap. 

 

 

Edited by Tumshie
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I used an epoxy coating over Vactan which worked really well but the tank was rusty to start with. You could always let it rust for a bit then Vactan it I suppose.

 

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If its a new tank in fairly clean steel then the obvious way is to take any surface rust off and do it in epoxy. However there might be an issue with millscale?

 

Derusting in five years time will be hard work so do the epoxy now! Not sure which epoxy to use though as Reactive Resins have gone bust. Any surface tolerant epoxy primer for the first two coats but then ideally you need a top coat with something that is safe for potable water.

 

Note that Vactan and its like are a very poor second best for cases when its not viable to get back to bare steel, and using it as an "insurance policy" on sound steel is very counter productive.

 

............Dave

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Fill it with cold tea, its tanning like Fertan ,install water heater, then you can have tea on tap. Tank will last for ever.

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23 minutes ago, Tumshie said:

Paging @Dr Bob - There'll be a muppet along here shortly. 

 

Don't worry he's a very clever muppet and is our resident / in-house paint expert, I saw him a moment ago so we may have just caught him before his afternoon nap. 

 

 

Can't a muppet have doze after a nice long lunch drinking lots of Estrellla galicia and a load of tapas?

 

12 minutes ago, dmr said:

If its a new tank in fairly clean steel then the obvious way is to take any surface rust off and do it in epoxy. However there might be an issue with millscale?

 

Derusting in five years time will be hard work so do the epoxy now! Not sure which epoxy to use though as Reactive Resins have gone bust. Any surface tolerant epoxy primer for the first two coats but then ideally you need a top coat with something that is safe for potable water.

 

Note that Vactan and its like are a very poor second best for cases when its not viable to get back to bare steel, and using it as an "insurance policy" on sound steel is very counter productive.

 

............Dave

Yeh, dont even think about vactan. It wont work on new steel.

If it is a new tank, is it steel or stainless steel? If Stainless then you dont need a coating. Go to the pub.

If it is new mild steel, as DMR says, make sure there is no mill scale. If there is it must be removed.

I would apply two coats of 2 pack epoxy. Look at the websites of International Paints or jotun and see if they have a potable water tank 2 pack epoxy. You wont go far wrong with those brands. Other brands are available. Make sure though that the surface is abraided as per paint manufacturers instructions.

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3 minutes ago, Dr Bob said:

Can't a muppet have doze after a nice long lunch drinking lots of Estrellla galicia and a load of tapas?

:DNope

Edited by Tumshie

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If I were you I wouldn't start from where you are. 

 

Get a nice plastic tank made and put it somewhere else. Then use the steel tank to keep junk in and never worry about rusty water again. 

 

Hope that helps.....

 

 

 

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31 minutes ago, Mike the Boilerman said:

If I were you I wouldn't start from where you are. 

 

Get a nice plastic tank made and put it somewhere else. Then use the steel tank to keep junk in and never worry about rusty water again. 

 

Hope that helps.....

 

 

 

Funny you should say that Mike, but I reckon plastic is the biss for water tanks, far better than stainless or built in tanks, which for me are stupid with a capital S! I now wait for the incoming fire from everybody with a rusty built in tank who thinks they are great

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7 hours ago, peterboat said:

Funny you should say that Mike, but I reckon plastic is the biss for water tanks, far better than stainless or built in tanks, which for me are stupid with a capital S! I now wait for the incoming fire from everybody with a rusty built in tank who thinks they are great

I have a built in Schrodinger's Water Tank... The water tastes fine and I don't get any rusty bits so it must be perfect - unless some idiot takes the lid off to find out. ;)

 

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9 hours ago, Mike the Boilerman said:

If I were you I wouldn't start from where you are. 

 

Get a nice plastic tank made and put it somewhere else. Then use the steel tank to keep junk in and never worry about rusty water again. 

 

Hope that helps.....

 

 

 

 

8 hours ago, peterboat said:

Funny you should say that Mike, but I reckon plastic is the biss for water tanks, far better than stainless or built in tanks, which for me are stupid with a capital S! I now wait for the incoming fire from everybody with a rusty built in tank who thinks they are great

I couldn't agree more. I've spent years in high performance coatings and more recently in plastics, specifically testing HDPE as tank materials. High density polyethylene is the best material for a potable water tank on a narrowboat. If you are short of room, put the PE tank inside the steel one. If you want to paint it, see my previous response. I didn't realize in my first post we could be innovative. Well done Mike.

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Dr Bob. I have heard it said from a supplier of plastic boat water tanks that pores in the plastic can absorb sterilising fluid and then taint the tank for some time afterwards. Personally I am also very interested in how plastic tanks cope with/react to sterilising fluid, especially the common ones based on bleach when the concentration is too high or it is left in the tank for too long.

 

Thanks.

Edited by Tony Brooks

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6 minutes ago, Tony Brooks said:

Dr Bob. I have heard it said from a supplier of plastic boat water tanks that pores in the plastic can absorb sterilising fluid and then taint the tank for some time afterwards. Personally I am also very interested in how plastic tanks cope with/react to sterilising fluid, especially the common ones based on bleach when the concentration is too high or it is left in the tank for too long.

 

Thanks.

Tony,

the failure mode for HDPE tanks is called 'environmental stress cracking'. The polyethylene used for tanks is therefore designed to have a high environmental stress crack resistance or ESCR. This failure mode sees microcracks form in the polymer due to chain scission and localalised brittleness. For HDPE's with very low ESCR (ie milk bottles, they dont have to last long!), a stress crack like this would grow very fast and crack the tank. For high ESCR HDPE, if a micro crack appeared then the resistance to crack growth due to the polyethylene structure will high and the crack will not grow. If therefore the tank is made out of decent HDPE with high ESCR then there is little problem. I think the 'pores' you talk about will be these cracks etc. It really isnt a problem if the right polymer is used. In BP, we used to make 50 different grades of HDPE - from milk bottles which are formulated for high flex modulus so they are stiff for very thin sections (ie cheap and low weight) but no UV stabiliser and poor ESCR.....but they only have to last a few weeks....to pipe grade HDPE which is formulated to have extreme ESCR allowing them to last 50 years for water and gas use.

Bottom line, if you go to a reputable tank maker, he will be using the right grade of HDPE. The cowboys may not and that is where the problem will lie.

We had HDPE tanks on our lumpy water boat (liveaboard) and we had no problems of taint.

That is the 'simple' response!!!!

Now the more complex one.

A number of fluids can enhance the stress cracking. Even simple detergents can reduce the stress crack resistance. Sterilising fluid, bleach and certainly hydrogen peroxide will accelerate stress cracking...but that is where the skill in making a decent ESCR polymer comes into play. In BP we tested all our polymers where ESCR was needed in all sorts of liquids using tests that could predict ultimate lifetime. I am now involved with the test lab that was spun out of BP as an MBO before BP divested its Chemicals interests to Ineos and we spend a large part of our work in testing for ESCR on polyethylene for both the manufacturers of the virgin polymer and the users...ie the big tank manufacturers. The test used for ESCR is an FNCT test (full notch creep test) where over a period of 24 hrs to a month, you can predict lifetime to 50 years. Basically you introduce a defect and apply a low controlled stress and obeserve the performance.

Bottom line....get the tank from a reputable manufacturer and you cant go wrong. Wash bleach or peroxide out as soon as practical and you will be ok. Dont leave it in for months!

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Just to put a balancing view, the integral water tank is rather out of fashion these days but it has huge advantages, especially now that good epoxies are available.

 

They give maximum available capacity for water and access to almost all faces is generally good. There are very few failures as long as minimal maintenance is done and no way that damp can build up around/under them like with a plastic or stainless tank. Why put a plastic/stainless tank in when the boat itself is already a tank?

 

...............Dave

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26 minutes ago, dmr said:

Just to put a balancing view, the integral water tank is rather out of fashion these days but it has huge advantages, especially now that good epoxies are available.

 

They give maximum available capacity for water and access to almost all faces is generally good. There are very few failures as long as minimal maintenance is done and no way that damp can build up around/under them like with a plastic or stainless tank. Why put a plastic/stainless tank in when the boat itself is already a tank?

 

...............Dave

 

Because there are no longer any coatings for integrated steel tanks that are 'food grade', IIRC. 

 

There was a long long thread about this a year or three ago. A bit of searching might turn it up.

 

I had an integrated tank in my first NB. I painted it with black 'water tank paint', bolted the hatch down an d proceeded to worry about the state of the inside of it for the next five years. When I finally took the hatch off to see what sort of rusty mess was sloshing about I was amazed to find it immaculately clean and looking as though I'd painted yesterday.

 

The 'water tank paint' was actually indistinguishable from hull blacking IIRC. 

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Maybe doctor Bob can help, but I assume that once epoxy is fully set that it is inactive and so safe, so any epoxy should be ok??? I suspect the "safe for potable water" is as much a paperwork exercise as a real chemical difference.

 

My only real worry about epoxy is that it might delaminate where the front of the boat gets a good bang. I really should have a look inside mine quite soon to see how it is doing, it was done quite a few years ago now. I might get one of those little USB camera things but I doubt they would show delamination unless the epoxy had also cracked.

 

Our friends up here have no mains water so are plumbed directly in to a spring. They test the water from time to time in case a dead sheep has fallen in upstream, so maybe we worry too much about water. I was surprised that their water tastes much much better than typical tap water, so we must already drink all sorts of stuff in our "clean" tap water.

 

..............Dave

there have been a fair few threads on this forum about rust coloured water from integral tanks but like you when I first looked inside my tank I was surprised how clean it was. I suspect the reputation for rust comes from a small number of older boats that have had zero maintenance. Its a bit like saying ALL Springers are crap and need overplating.

 

..............Dave

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The reason we had rusty water from an integral tank appeared to be that the pipe coming out of the tank was made of mild steel.  While the tank itself was regularly repainted with water tank black, it was impossible to treat the inside of the pipe.  We do not regret our decision to have a 'plastic' tank installed inside the integral one over 20 years ago.  We don't use tank cleaning chemicals and, as holiday boaters, simply give it a good flush through every Spring and the water tastes fine.  For boat visits or trips during the winter, we fill a water carrier for drinking purposes.

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On 17/04/2019 at 14:52, dmr said:

If its a new tank in fairly clean steel then the obvious way is to take any surface rust off and do it in epoxy. However there might be an issue with millscale?

 

Derusting in five years time will be hard work so do the epoxy now! Not sure which epoxy to use though as Reactive Resins have gone bust. Any surface tolerant epoxy primer for the first two coats but then ideally you need a top coat with something that is safe for potable water.

 

Note that Vactan and its like are a very poor second best for cases when its not viable to get back to bare steel, and using it as an "insurance policy" on sound steel is very counter productive.

 

............Dave

 

Agreed. If you can find a water potable epoxy supplied in small quantities then that's the way to go. It's better to remove any rust properly rather than use Vactan.

36 minutes ago, dmr said:

Maybe doctor Bob can help, but I assume that once epoxy is fully set that it is inactive and so safe, so any epoxy should be ok??? I suspect the "safe for potable water" is as much a paperwork exercise as a real chemical difference.

 

 

 

No, an ordinary epoxy will contain benzene or xylene and will taint the water. It must be water-potable. You can use an ordinary epoxy as a base coat and overcoat it with a compatible water potable grade.

Edited by blackrose

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36 minutes ago, dmr said:

Maybe doctor Bob can help, but I assume that once epoxy is fully set that it is inactive and so safe, so any epoxy should be ok??? I suspect the "safe for potable water" is as much a paperwork exercise as a real chemical difference.

In practise you are right. If properly cured, then epoxy will be inactive and all 'nasties' tied into the 3d thermoset network. The problem is caused when the paint company uses 'special' curing agents/accelerators or puts in surface active agents that dont react in ...or if it isnt cured properly. You are also right that most companies now are just pulling the 'potable water' status as it is too expensive to test or provide the paperwork required. I think coal tar containing paints will always be a problem as coal tar does contain carcinogens which may not all react in.

For me, I wouldnt get too worked up about it. A well cured epoxy should be fine. If it did have any nasties left in it after cure, it wont be much and soon washed out. I would avoid a coal tar epoxy but I would be happy with the rest.

I would be far more worried about all the bacteria in our hose pipe that could give us all sorts of diseases.....after the end keep falling in......but then we dont really worry about that and still drink the tank water without a thought. We havent died......yet. The duck is still alive.

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21 minutes ago, blackrose said:

 

No, an ordinary epoxy will contain benzene or xylene and will taint the water. It must be water-potable. You can use an ordinary epoxy as a base coat and overcoat it with a compatible water potable grade.

I was assuming it was well cured so the majority of the solvents will come out during cure. A little bit of benzene or xylene will not kill you. I would be happy using a 'typical' epoxy well cured.

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Many thanks Dr B for very informed input on a specialist subject thatw eoften find difficult to get difainative answers.

 

Cheers

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There are a couple of substances (plutonium?) where I believe a single atom/molecule in the wrong place can be fatal, but otherwise its just a case of diluting things down to a safe dose (unless you believe in homeopathy :)). When we wash our hands in a bowl of water all we are doing is diluting the dirt to a safe dose. Surgeons scrub up by washing their hands under Running water for a long time.

 

Tap water has been used many times and contains all sorts of stuff, but hopefully at a very low concentration.

 

Always run some water through your hose before filing the tank, and when the end drops in the cut then rinse it under the running tap.

 

.................Dave

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2 hours ago, dmr said:

Maybe doctor Bob can help, but I assume that once epoxy is fully set that it is inactive and so safe, so any epoxy should be ok??? I suspect the "safe for potable water" is as much a paperwork exercise as a real chemical difference.

 

My only real worry about epoxy is that it might delaminate where the front of the boat gets a good bang. I really should have a look inside mine quite soon to see how it is doing, it was done quite a few years ago now. I might get one of those little USB camera things but I doubt they would show delamination unless the epoxy had also cracked.

 

Our friends up here have no mains water so are plumbed directly in to a spring. They test the water from time to time in case a dead sheep has fallen in upstream, so maybe we worry too much about water. I was surprised that their water tastes much much better than typical tap water, so we must already drink all sorts of stuff in our "clean" tap water.

 

..............Dave

there have been a fair few threads on this forum about rust coloured water from integral tanks but like you when I first looked inside my tank I was surprised how clean it was. I suspect the reputation for rust comes from a small number of older boats that have had zero maintenance. Its a bit like saying ALL Springers are crap and need overplating.

 

..............Dave

We had tanks blasted and epoxy coated for potable water when I worked Offshore, but they were big enough to get into with a blast gun and airless spray

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2 hours ago, Dr Bob said:

I was assuming it was well cured so the majority of the solvents will come out during cure. A little bit of benzene or xylene will not kill you. I would be happy using a 'typical' epoxy well cured.

Ok I didn't say it would kill you but I think some of the solvents will remain and taint the water. I've never actually tried it myself, but when I asked Jotun's technical manager he told me not to do it for that reason.

 

Why wouldn't you use a potable water compatible epoxy that's designed for the job rather than one that isn't?

Edited by blackrose

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3 hours ago, Mike the Boilerman said:

 

Because there are no longer any coatings for integrated steel tanks that are 'food grade', IIRC. 

 

There was a long long thread about this a year or three ago. A bit of searching might turn it up.

 

I had an integrated tank in my first NB. I painted it with black 'water tank paint', bolted the hatch down an d proceeded to worry about the state of the inside of it for the next five years. When I finally took the hatch off to see what sort of rusty mess was sloshing about I was amazed to find it immaculately clean and looking as though I'd painted yesterday.

 

The 'water tank paint' was actually indistinguishable from hull blacking IIRC. 

 

I'm not sure about "food grade" but there are plenty of potable water paints both bitumen based and epoxy:

 

https://www.international-marine.com/type/potable-water-tank-coatings

 

https://www.jotun.com/zw/en/b2b/paintsandcoatings/products/tankguard-dw.aspx

 

https://www.thompsonsweatherproofing.co.uk/media/1343/j4016-thompsons_bitumen-paint-data-sheets_st2.pdf

 

Also I'm not really sure how you'd get a big rigid plastic tank into an integral tank when a typical access hatch is only about 18" square? Unless you're going to cut the deck out! You could have lots of smaller linked tanks I suppose but you'd lose a lot of the volume and the hoses between might freeze in winter.

 

 

 

Edited by blackrose

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