Rust Suffocation?

[Honey Ryder]

I am wondering about the efficacy of dealing with rust in an unconventional way and wonder if anybody has tried it before?

Looking at basic chemistry, it seems that normal rust can not occur without oxygen.

From Wikipedia: "Rust is a general term for a series of iron oxides. Colloquially, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture."

My buddy and I have stripped out the entire interior of my boat right back to the steel hull, and are now prepping it ready for painting and the re-fit.
We have some surface rust caused by condensation that did not drain away, and some deep pits under two port holes where water got in and couldn't evaporate (insulation) or drain away (lack of limber holes in the steel horizontals - now rectified).

Everybody knows that the best way forward is to shotblast and then prime/paint. For logistic reasons this is not easy, so we are trying to think up an alternative solution...and the subject of suffocation arose.

The idea is this, remove as much rust as possible through multiple applications of phosphoric acid plus grinding/wire brushing. Then apply Vactan/Fertan type tannic acid coating, followed by high zinc primer, followed by...and this is the big question....a thick layer of rubber paint.

Why rubber paint?

There is a rubber paint which can flex 500-700%, which means a 1mm coating can expand 5-7mm, without breaking. Once covered with this paint, any residual rust will do what rust does and use up more healthy steel to make more rust, and it will use up the available oxygen to do so. Eventually, the oxygen under the paint will all be sued up. The rust process should then stop, correct? As the healthy steel rusts a little, it will expand as rust does, but the rubber paint should flex, instead of breaking, as normal paint would do. So, whereas the normal paint would break and let in more oxygen and allow the rusting process to continue unchecked, the rusty steel that is covered with the rubber paint should suffocate because there is no fresh oxygen being delivered to the rust underneat the paint. It is a bit like putting a plastic bag over your head, eventually you will die.

Can anyone see a reason why this wouldn't work?

A friend of mine has a 100 year old iron/steel barge. He says that in the deep recesses of the hull there is ancient coal tar, which is very thick. There is no rust. It seems to have worked well on his boat.

So, can anyone think of a reason why I can't skip the shotblasting and just suffocate all the steel on the inside of the hull with a really think layer of rubber paint, and let the rust underneath die of oxygen starvation?

[David M]

You got it. Starve iron of oxygen and you stop rust. There are hundreds of ways of doing this. Which method is best depends on the application.

Unfortunately applying coatings over iron oxide is not very effective because iron oxide does not provide a very secure base for coatings to physically adhere to. We have all seen how easily rust flakes off. It's analogous to painting a road completely covered with loose rocks.

What I like doing with steel is to knock off all the loose stuff, however it is done, and then apply a few epoxy barrier coats. As long as the epoxy does not get damaged, then you have cut off the supply of oxygen AND the epoxy has a good solid base to stick to.

I really like Interlux 2000 for this. This stuff is tough as nails. I drop metal oceanographic gear, anchors and weights on it on my afterdeck all the time and it holds up extremely well. Something like West System type epoxy is not what I am referring to. This type of epoxy would not hold up as well to UV and the type of abuse I described.

You would want 3 coats at the bare minimum.

[minaret]

x2 on Interlux 2000. We use it for coating steel pretty often and it is really stout. And you know it's providing an excellent moisture barrier. It seems to bond to steel better than just about anything I've come across. It would be perfect for a hull interior as suggested by previous poster. I'd do 4 coats or so. Of course then you can't see any new rust problems developing under it...

[Unicorn Dreams]

I used a coal tar epoxy on Santana, 5 coats each side.
Can't comment on the Interlux 2000..

[Honey Ryder]

when you applied the epoxy directly to the steel, was the steel shotblasted, or just grinded/wire brushed/ acid treated?

i am concerned that the little bit of rust that remains in the pits will cause me problems by expanding by using up what little bit of oxygen remains under the epoxy, and that the expansion will cause the epoxy to break free from the steel and let in more oxygen. or was this not a problem? did the epoxy remain stuck to the steel? did this last or did the rust eventually come through again?

[David M]

No worries about that. What tiny amount of oxygen is left will turn to iron oxide and although iron oxide expands, so does the epoxy slightly. There is enough barrier coat where you still have an effective oxygen barrier. Just do as much as you can within your means to get rid of the rust and don't sweat a tiny amount here and there. Just make sure the metal is clean and oil free. An acid wash with phosphoric acid is not really necessary. I would prefer to not have any of its crystals left on there in fact. Bare clean bright steel is best.

[Boracay]

Have you considered using POR 15?

I have tried quite a few paints and coating since I got Boracay and yes, the epoxy should work. In particular I've found that if I pour some generic 5:1 epoxy resin into where water has pooled (totally dry, clean, treat and redry first) then it seems to stick quite well. I overcoated this with a good quality single pack epoxy "metal" enamel. I don't know how long this would last so constant checking is necessary.

However if you look at the POR15 web site you'll see they use a three step process. This is what I used last time Boracay came out of the water. I did a couple of trial runs first, just to check. So far so good...

What I found from the trial runs was that the POR15 needs to go on quite thin, with multiple coats being used. If it goes on too thick it foams (a little like polyurethane glue) and the protection is compromised.

For the 3 step process it uses what feels like a very good quality water soluble degreaser ("Marine Clean") to totally clean first, the "Metal Ready" acts as an etch primer, and the "POR 15" is put on in very thin coats (at least 3). The POR15 needs to be protected with a top coat.

For my trial run I used a Ryobi Rotary tool with a diamond ball bit (came in the kit) to get every scrap of rust out. When Boracay was out of the water the shipwright used a 40 grit flapper disk (I had ordered some el cheapo diamond bits off the internet but they came late) and there did not look to be any rust left.

There is an article in Coastal Passage Magazine that presents the process better than me.

Its a lot more work than a quick scrub and coat of paint.

[Delfin]

When I purchased our boat, it was an empty shell, but primed and painted. To insulate the metal so that condensation could not occur, we applied liquid nails with a notched trowel, then applied 1/4" acoustical cork. My advice would be to apply Corroseal to the hull, which chemically bonds with oxidation and creates a great base for a primer coat. Some rust is necessary for it to work, so having surface rust is a benefit, not a problem. After that, I would prime the metal, then apply Quiet Ship (we used this product) and do what we did - glue cork over all metal surfaces. You will never have condensation, you'll seal the surface with a something similar to your rubber paint, but the cork will make the boat as quiet as a boat can be, or at least that is my experience.

A photo of the cork as applied is below. The gray visible is the Quiet Ship acoustical deadening compound we used. The cork is available from Jelinek.

[cat man do]

Originally Posted by Delfin

The gray visible is the Quiet Ship acoustical deadening compound we used. .

I couldn't find Quiet Ship, but I did find Quiet Car QuietCar 5 Gal.
I imagine it could be cheaper as it does not have "ship" in the name?

Sounds like its along the lines of Silent Running - high performance sound and vibration dampening coating for marine vessels

How did you find it?
I have considered using it in the engine room in favour of the heavy barium impregnated foam

[Delfin]

Originally Posted by cat man do

I couldn't find Quiet Ship, but I did find Quiet Car QuietCar 5 Gal.
I imagine it could be cheaper as it does not have "ship" in the name?

Sounds like its along the lines of Silent Running - high performance sound and vibration dampening coating for marine vessels

How did you find it?
I have considered using it in the engine room in favour of the heavy barium impregnated foam

That's the stuff. The utility is to deaden sound communicated through vibration. It doesn't do much for sound communicated through the air, so won't replace barium foam. However, as part of a comprehensive approach to sound deadening, it is the poop, and also protects the steel. It goes on about 10 mils thick and sticks like crazy.

I bought it from Hamilton Marine when it was first developed for X class attack boats, which are made of aluminum. At 50 knots, the vibration was so intense the crew was bleeding through their eyeballs after a few miles. The Quietship deadened this vibration and makes the boats tolerable for humans.

[psneeld]

Have read that ANY amount of rust has enough O2 in it to keep rust going indefinitely...not sure who said it...but it seems to be true...never have heard of rust suffocation before and I'm sure it would be a hot topic in the marine world if it worked.

[Delfin]

Originally Posted by psneeld

Have read that ANY amount of rust has enough O2 in it to keep rust going indefinitely...not sure who said it...but it seems to be true...never have heard of rust suffocation before and I'm sure it would be a hot topic in the marine world if it worked.

That is what Corroseal negates. It chemically reacts with the rust, creating a base for an appropriate and long lasting solution.

[cat man do]

Originally Posted by Delfin

That's the stuff. The utility is to deaden sound communicated through vibration. It doesn't do much for sound communicated through the air, so won't replace barium foam. However, as part of a comprehensive approach to sound deadening, it is the poop, .

I could see how it works on metal. The video they have here

YouTube - ‪A Simple Demonstration of How QuietCoat's Core Technology Works‬‏

is the same sort of test I was shown in Oz with the "Silent Running"
But I was not convinced that a Timber or foam cored vessel would ring like a metal drum
And no one could point me to a vessel that actually had it on so as I could see for myself

It was always "This guy with a Bertram says its fantastic, go see it..", but I could never get to meet him as he was always up the reef or down in Sydney or perhaps an imaginary client?

Its a shame as I really am interested, but probably not enough to experiment with my own money just yet

Probably should start a new thread if this discussion continues and leave this to the oxygen starved rust

[psneeld]

Originally Posted by Delfin

That is what Corroseal negates. It chemically reacts with the rust, creating a base for an appropriate and long lasting solution.

I've been using corroseal for over 30 years..it works sometimes and most of the time not...the prep is crucial and seems to be hit or miss because if you miss even a microscopic bit of rust...it's starts all over..and I'm not alone because the company I work for uses it by the 55 gallon container.

I say there are other just as effective methods..which a lot of others use/try...

What I'm saying is that you can't "smother" rust...you either eliminate it or convert it...but if there's even a tiny bit of "rust" left....it returns with vengence.

[GordMay]

Originally Posted by psneeld

... What I'm saying is that you can't "smother" rust...you either eliminate it or convert it...but if there's even a tiny bit of "rust" left....it returns with vengence.

As noted, you want to convert rust to black oxide, and protect that coating.

Rust is really Fe2O3, a reddish form of iron oxide. Iron has another oxide, Fe3O4, which is sometimes called “black oxide”, “black rust” or “hammerscale”.

Black oxide is a good protection for steel. Like aluminum oxide, black oxide molecules are the same size as iron molecules, so black oxide doesn’t grow or flake. Black oxide is true gun bluing, and the oxide found on some drill bits. Black oxide is also seen on iron and steel that has been hot-worked.

You can coat steel with black oxide by a careful regimen of rusting the right amount and boiling the rusted metal in water to convert it. This is how non-caustic gun bluing is done, and although it is tedious, it produces very attractive and durable results after several treatments.

When iron or steel starts to rust, it will puff up and expose clean metal to the open air, allowing rust to continue to the depths of the metal. There are a few products on the market which fall into the category of organic rust converters. These products contain phosphoric acid to convert rust to black oxide and polymers which bond to rust.

A unique advantage of phosphoric acid is that it leaves a fine coating of iron phosphate behind. Iron phosphate prevents rust. However, the iron phosphate coating is not very thick and not durable. Some additional protection is still required.

Auto body shops treat metal with acid metal wash, a solution of phosphoric acid, and alcohol before painting. Acid etching using phosphoric acid involves:
- Getting rid of waxes and oils on the metal surface
- Removing slight amounts of rust that form between sand blasting and painting
- Leaving a thin protective coat of iron phosphate