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Treating black rust on the inside of a heavily pitted bilge.


DHutch

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What a lovely job!

 

Why didn't the paint stick?

 

Attached are some images of our bilge, which we have previously prep'd about as well as we can; scrapping, needle scaling, angle grinding off the highest points, mechanically wire brushing with a grinder, and all that sort of good thing. 

Then we got it and clean and dry as we could, treated it with Vactan, let that dry well, and then have it two coats of high quality 2pack epoxy aluminium. Only to find two years later when we came to give it another coat, significant amount of it are coming of in sheets. 

 

Some of the less pitted and or dryer bits are well adhered still, some bits are less and ideally adhered, but remain coherent, just about stuck, and dry underneath. But most worryingly, some area have individual 'mushrooms' of corrosion at each pit when the coating had clearly failed and it's damp under the paint. Arse. 

 

What do we do next, giveb doing at all again seems slightly foolhardy?

 

Grit blasting or even shot blasting back to bright would be ideal, due to the fact it's inside the boat and not many places offer the service anyway, that's perhaps not practical.

 

So what do we do? 

 

Is there an alternative rust conversion routine? A different paint alternative?

 

Some might just out down half a gallon of old engine oil, but that's awful messy and a bit of a one way ticket.

 

Thoughts very much welcome!20210922_120119.jpg

 

Daniel

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It's possible that the latex primer element of the Vactan is failing. Yes.

 

However Vactan can be used with, according to their literature, anything other than cellulose. With their example being a 2pack polyurethane acrylic paint, which is what we then out over the Ali primer. 

We have used Vactan with good success with this paint system elsewhere. If not under standing water.

 

Hence I mildly lean towards the issue being we haven't removed enough of the black ferrosoferric rust from the base of the pits for it to get good treatment and or adherence. But I don't know how to remove more and or better.

 

Get putting the ali epoxy direct onto bright steel would be lovely, but that isn't what we have and I don't have a good way to get it back to bright.

The ali epoxy in question specifically mentions it is a brushing epoxy, for use with manually prepared surfaces, and claims to be toleratant of slightly damp substrates. 

 

 

Daniel

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I like Owatrol.  I know some are sceptical but I've used it in situations like this where it's just not possible to do anything more than remove the loose rust and it works for me.  Ever since the demise of Trustan I don't think there's ever been an effective rust converter.

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That's odd. That's around the engine where usually you would expect it to be a bit oily. That might suggest that the steel was in fact a bit oily when you applied the paint despite your considerable efforts. Is that under a cruiser deck and therefore a bit dampish? I have found that some very good paints really do not like being permanently wet or under puddles, they just do not stick. Actually, looking at the last picture there seems to be a bit of a tideline that suggests water has collected there. If that is the case I think the answer is to keep it dry and that could be a challenge. You might even find that water tank paint is a solution. 

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The corrosion mushrooms round the pits tell you what the main problem is: ongoing corrosion cells at the base of the pits.   Can you pressure wash the pits before Vactan  or, better because it can be diluted to help get it into the base of the pits, Fertan?  If not, inhibited Phosphoric acid treatment , worked well into the pits should help.  You could alternatively try Spirits of Salts (HCl). Available for toilet descaling.  Very effective on rust but  likely to make any bare steel nearby go rusty very quickly.

 

What was the water temperature when you painted? If the boat is in the water it is quite common for the water temp to be near enough to the dew point to get a  fine layer of damp on the steel.  Not many paints will stick well to steel near the local dew point.

 

N

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4 minutes ago, BEngo said:

The corrosion mushrooms round the pits tell you what the main problem is: ongoing corrosion cells at the base of the pits.   Can you pressure wash the pits before Vactan  or, better because it can be diluted to help get it into the base of the pits, Fertan?  If not, inhibited Phosphoric acid treatment , worked well into the pits should help.  You could alternatively try Spirits of Salts (HCl). Available for toilet descaling.  Very effective on rust but  likely to make any bare steel nearby go rusty very quickly.

 

What was the water temperature when you painted? If the boat is in the water it is quite common for the water temp to be near enough to the dew point to get a  fine layer of damp on the steel.  Not many paints will stick well to steel near the local dew point.

 

N

The thought that it was painted whilst in the water occurred to me too.  Your breath alone will cause condensation on the steel as you paint. I find the only way to do water tanks whilst the boat is in the water is to use a fan heater inside the tank for a hour or so before any paint goes on.

 

If its "black rust" it would suggest to me that is is really iron that has been converted by the tannin in Vactan or Fertan that has grown due to damp trapped under the paint layer.

 

Phosphoric acid is easier to get to soak into the rust remaining but then you have to be careful what you overpaint with.

 

I have had poor results with Danbolin in bilges with the same result that you have discovered.

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Have had exactly the same in our hold.

At the back where it can get water lying.

3 years ago i ground off, with wire wheel in grinder derusted, double primed, top coated in gloss and then waxoiled.


lifted shuts this week and failures everywhere.

chipped it off, fertanned it, and waxoiled on top. Cant be any worse.

 

the next bay i had treated 2 years ago but instead of paint and primer i just waxoiled. This looks intact.

 

so maybe the answer.

Admittedly im dealing with a 20 year old bottom, that until the cabin extension went on was in the middle of the boat under bulk diesel tanks, but i honestly think you cant stop it, however fancy the products.

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2 hours ago, Bee said:

That's odd. That's around the engine where usually you would expect it to be a bit oily. ...... Is that under a cruiser deck and therefore a bit dampish? 

The boat has an engine room, so although it's the location most boats would have their engine, their is no oil or engine in sight.

 

Even more unusually, space is under the wheelhouse. So it is much dryer than a cruiser stern might be, especially now we tape up the back deck access hatch behind the wheelhouse which stops most rain getting in. However it is a bildge, we do sometimes boat in the rain with the wheelhouse down for bridge clearance, and it's not uncommon for their to been a bit in the corners! Which is properly almost worse than being properly wet all time. 

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2 hours ago, BEngo said:

The corrosion mushrooms round the pits tell you what the main problem is: ongoing corrosion cells at the base of the pits....

 

....What was the water temperature when you painted? If the boat is in the water it is quite common for the water temp to be near enough to the dew point to get a  fine layer of damp on the steel.  Not many paints will stick well to steel near the local dew point.

Canal temperature. During mid autumn if we do it tomorrow, sunny and dry. We have in the past done it while on dryock, but they are dam places too!

 

We have used a fan heater in there several times before. She's not been cleaned out in 30 years and we usually dry dock in September. 

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2 hours ago, BEngo said:

The corrosion mushrooms round the pits tell you what the main problem is: ongoing corrosion cells at the base of the pits. 

 

  Can you pressure wash the pits before Vactan  or, better because it can be diluted to help get it into the base of the pits, Fertan? 

 

If not, inhibited Phosphoric acid treatment , worked well into the pits should help.  You could alternatively try Spirits of Salts (HCl). Available for toilet descaling.  Very effective on rust but  likely to make any bare steel nearby go rusty very quickly.

 

We proberbly just about could pressure wash it if we had to, having first sheeted up the alternator, solar controller, and the back of the plywood bulkhead to the boat. I am not sure how much that would get off that the needle scaller wouldn't, even if it's better and deep pits I don't know if it would have the bite to get through to the black rust. 

 

We've not used Fertan, mainly because of the faff of having to rinse it off again, but I'll try most things atleast once and atleast it would remove the possibility of it being the Vactan primer that's failing?

 

Phosphoric acid is another option, presumably also needing rinsing. Ditto Hydrochloric acid.

 

 

 

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Epoxy is good stuff, its weakness appears to be that it does not stick too well to some surfaces and tends to lift off in sheets. I suspect the Vactan is at least part of the problem, its a second best fix when you can't do a proper job and probably not a brilliant primer.

 

If you can get almost to bare metal (and a needle gun should do that) then apply a surface tolerant epoxy primer direct to steel, after suitable cleaning. Otherwise I have used Red Owatrol and then a couple of coats of bilge paint (Danboline or similar) and that has been good for 7 or 8 years so far. The red Owatrol took several days to dry.

 

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27 minutes ago, roland elsdon said:

Have had exactly the same in our hold.

At the back where it can get water lying.

3 years ago i ground off, with wire wheel in grinder derusted, double primed, top coated in gloss and then waxoiled.

 

I did Ryan's Southern Cross over the summer, at the back against the cabin it was very bad, spent 2 days with a needle gun working my way up to the diesel tank. We have used Aquasteel as the coating below the deck boards, nothing else, and will see how effective it is in 2 years....when we get the pleasure of doing the front end..

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5 minutes ago, dmr said:

Epoxy is good stuff, its weakness appears to be that it does not stick too well to some surfaces and tends to lift off in sheets. I suspect the Vactan is at least part of the problem, its a second best fix when you can't do a proper job and probably not a brilliant primer.

 

If you can get almost to bare metal (and a needle gun should do that) then apply a surface tolerant epoxy primer direct to steel, after suitable cleaning. Otherwise I have used Red Owatrol and then a couple of coats of bilge paint (Danboline or similar) and that has been good for 7 or 8 years so far. The red Owatrol took several days to dry.

 

When you say Red Owatrol, which Owatrol product is it exactly please?

 

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2 minutes ago, Ryeland said:

When you say Red Owatrol, which Owatrol product is it exactly please?

 

 

I think its called Owatrol CIP (corrosion inhibiting primer?). I did my back bilge in it (and bilge paint) about 8 years ago just as a stop gap and its only just starting to fail now.

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@roland elsdon I insist waxoyl is the wrong stuff to use in a boat.  It's great for underneath vehicles, but it's designed to let any trapped water seep through it eventually.  You want this on a chassis and floorpan, but you certainly don't want this inside a bilge as any standing water will end up between the baseplate and the waxoyl layer.

 

@DHutch owatrol is good stuff.  If you get the pure oil you can mix it with most paints (rtfm though!) or as @dmr says they do a range of premixed paints/primers.

 

My engine room floor gets done in Aldi's Direct to rust metal paint at about three year intervals, but this time I did it while in the dry dock and it seems better than doing in the water like last time. 

 

It's basically a hard-wearing gloss paint with something like owatrol mixed in, but it's a fiver a litre so I generously coat it whenever it looks too tatty.  At that price you could nearly tip it in and slosh it around a bit ...

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51 minutes ago, dmr said:

Epoxy is good stuff, its weakness appears to be that it does not stick too well to some surfaces and tends to lift off in sheets. I suspect the Vactan is at least part of the problem, its a second best fix when you can't do a proper job and probably not a brilliant primer.

 

If you can get almost to bare metal (and a needle gun should do that) then apply a surface tolerant epoxy primer direct to steel, after suitable cleaning. Otherwise I have used Red Owatrol and then a couple of coats of bilge paint (Danboline or similar) and that has been good for 7 or 8 years so far. The red Owatrol took several days to dry.

 

 

I'm convinced that those who reckon Owatrol doesn't work do not follow the instructions, and/or lose patience with it as it can take some time to cure.  

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You prepared the surface as well as possible, and then applied Vactan?

 

If so, that's the problem. Vactan does not bond well to very clean steel. It is designed to bond to well adhered rust, converting it in the process. If there is no rust for it to convert it does not bond so that is the interface which fails. The interface between the Vactan and the epoxy does not fail as it is stronger.

 

Three approaches to consider:

 

1. Clean back to bare, clean metal with all rust removed and paint with an epoxy primer and polyurethane topcoat. If the surface is clean enough, this will bond very well and form a long-lasting barrier.

2. Clean back anything loose and convert the surface - depends how good that cleaning is but Vactan/Fertan will work well so long as there is a layer of well bonded rust whereas phosphoric acid based treatments will work if the surface is mostly clean but with some rust down the pits on the surface. I prefer phosphoric acid with zinc phosphate added as it is very protective for a long time (I have left bare steel treated with this in a damp shed for 2yrs and it hasn't corroded). Then paint over this with a good single pack primer and topcoat. It can't be expected to last as long as 1 but will still last a good few years and is much easier to renew.

3. Clean back to bare metal and apply a metal-loaded paint, usually with aluminium or zinc (metal, not phosphate). The sacrificial metal will provide protection to the steel just like an anode, or galvanising. The paints are generally more expensive and softer so will not withstand knocks and bumps so well. They can be overcoated with a decent topcoat which will protect them for longer, but the weak bond tends to be within the metal loaded paint so they do chip more easily. If you go down this route, do not put anything on the steel before the paint - you need an electrical connection which won't work through a conversion layer or other paint.

 

Hope this helps

 

Alec

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5 hours ago, cuthound said:

I'm not a paint expert but 2 pack paints usually go straight onto bare metal or a suitable 2 pack primer.

 

Could it be that the primer part of the  Vactan is failing?

 

That would be my thought too.

 

Why would you put an epoxy on top of what's essentially a water based primer?

 

There's nothing wrong with the tannic acid element of vactan in converting rust. What's much more suspect in my experience is the longevity of the water based polymer matrix.

Edited by blackrose
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50 minutes ago, agg221 said:

You prepared the surface as well as possible, and then applied Vactan?

 

If so, that's the problem. Vactan does not bond well to very clean steel.

While prep'ed about as well as we could, given the initial conditions, there was very little bright steel. And the best and least pitted areas where maybe only 50% bright steel, and are the area the paint had stuck best! So while under the concert, it wasn't what was happening here. 

 

As per the 'Misuse of rust converters' thread I have yet to find this mystic 'easy to remove rust' as most rust is in the hard to reach spaces of the world (for obvious reasons) and even if access is good, grinding anything back to bright takes an age!

 

https://www.canalworld.net/forums/index.php?/topic/104614-the-misuse-of-rust-converters-the-vactan-myth/page/2/

 

So having ruled out 1.  (Which also includes a metal loaded epoxy) we're onto option 2.

 

50 minutes ago, agg221 said:

2. Clean back anything loose and convert the surface - depends how good that cleaning is but Vactan/Fertan will work well so long as there is a layer of well bonded rust whereas phosphoric acid based treatments will work if the surface is mostly clean but with some rust down the pits on the surface. I prefer phosphoric acid with zinc phosphate added as it is very protective for a long time (I have left bare steel treated with this in a damp shed for 2yrs and it hasn't corroded). Then paint over this with a good single pack primer and topcoat. It can't be expected to last as long as 1 but will still last a good few years and is much easier to renew.

 

 

I'm warming to the idea of phosphoric acid and zinc phosphate as an option. What are we looking at here, in terms of a process, and required materials. Aka, where do we get the stuff and what to do we with it?

 

 

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41 minutes ago, agg221 said:

You prepared the surface as well as possible, and then applied Vactan?

 

If so, that's the problem. Vactan does not bond well to very clean steel. It is designed to bond to well adhered rust, converting it in the process. If there is no rust for it to convert it does not bond so that is the interface which fails. The interface between the Vactan and the epoxy does not fail as it is stronger.

 

Three approaches to consider:

 

1. Clean back to bare, clean metal with all rust removed and paint with an epoxy primer and polyurethane topcoat. If the surface is clean enough, this will bond very well and form a long-lasting barrier.

2. Clean back anything loose and convert the surface - depends how good that cleaning is but Vactan/Fertan will work well so long as there is a layer of well bonded rust whereas phosphoric acid based treatments will work if the surface is mostly clean but with some rust down the pits on the surface. I prefer phosphoric acid with zinc phosphate added as it is very protective for a long time (I have left bare steel treated with this in a damp shed for 2yrs and it hasn't corroded). Then paint over this with a good single pack primer and topcoat. It can't be expected to last as long as 1 but will still last a good few years and is much easier to renew.

3. Clean back to bare metal and apply a metal-loaded paint, usually with aluminium or zinc (metal, not phosphate). The sacrificial metal will provide protection to the steel just like an anode, or galvanising. The paints are generally more expensive and softer so will not withstand knocks and bumps so well. They can be overcoated with a decent topcoat which will protect them for longer, but the weak bond tends to be within the metal loaded paint so they do chip more easily. If you go down this route, do not put anything on the steel before the paint - you need an electrical connection which won't work through a conversion layer or other paint.

 

Hope this helps

 

Alec

 

Sounds like you know about this stuff, so a few comments/questions?

 

1 If its inside the boat I don't think the epoxy needs a single pack topcoat, and leaving the epoxy uncoated makes it easier to repair/recoat in the future.

 

2 Is there a "ready made" phosporic acid-zinc phosphate "paint" available?

 

3 Are you talking about the likes of Zinga/Galvafroid here? Lots of people rave about ZingA stuff but I had not heard that it chips easily. I need to do my baseplate soon, should I go for epoxy or Zinga + epoxy?

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8 minutes ago, blackrose said:

 

That would be my thought too.

 

Why would you put an epoxy on top of what's essentially a water based primer?

 

There's nothing wrong with the tannic acid element of vactan in converting rust. What's much more suspect in my experience is the longevity of the water based polymer matrix.

 

Because we can't get the prep good enough for direct epoxy application. We know that, because we have done that in this area too! Which was in drydock as well.

 

Often we get good success with Vactan+epoxy ali. Just not here. 

 

Maybe we should be using a rust converter without a primer element, and I am open to recommendations.

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2 hours ago, harrybsmith said:

Did you get the mix right on the 2k in the first place? Too much hardener can lead to a brittle coating 

The epoxy ali we use is harder, and more brittle than some, certain compaired to dacrylate which appears to remain reasonable soft even 24-48hour in when I assume it's reached effectively full cure.

 

However, we understand the importance of a good mix, and mixed all our two part paints (epoxy and the acrylic urethane topcoat) carefully and accurately using a microbalance and the manufacturers guidelines, including running out of the two parts at about the same time which is always a good indication!

 

Daniel

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