Silly question about rusty ballast

Rivers & creeks

Rivers & creeks

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We have some rusty concrete encapsulated ballast - a grounding some years ago must have left a small leak and an area about the size of a shoe box has obviously been wet. This is a dumb question, but as iron rust it expands - does that mean it will swell the keel area and cause structural problems? But having said that, there is about 5 tonnes of iron punchings, lathe scrappings and stone, all of that will surely be rusty anyway since it hardly went into the hull in 0% humidity and concrete is full of water. The iron ballast at the bottom of the keel however may not be encased in concrete - can't be 100% sure.
BTW there is no deformation to the hull and no other signs of problems.
 
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The Lazy Kipper said:
We have some rusty encapsulated ballast - a grounding some years ago must have left a small leak and an area about the size of a shoe box has obviously been wet. This is a dumb question, but as iron rust it expands - does that mean it will swell the keel area and cause structural problems? But having said that, there is about 5 tonnes of iron punchings, lathe scrappings and stone, all of that will surely be rusty anyway since it hardly went into the hull in 0% humidity!
Silly question - not sure but there is no deformation to the hull and no other signs of problems.
Click to expand...

ask Ralph ;)
 
Yes rust can cause serious damage if the metal is encapsulated. It doesn't rust because the conditions for rust to form are not present in an encapsulated keel. If water is introduced then the conditions may exist for rust to form. After all steel rusts away under water.

There are plenty of examples where the laminate has been damaged by the expansion of rust, but also examples where it all just ends up a big mess with no damage. Either way it needs to be investigated and repaired as appropriate.
 
BlowingOldBoots said:
Yes rust can cause serious damage if the metal is encapsulated. It doesn't rust because the conditions for rust to form are not present in an encapsulated keel. If water is introduced then the conditions may exist for rust to form. After all steel rusts away under water.

There are plenty of examples where the laminate has been damaged by the expansion of rust, but also examples where it all just ends up a big mess with no damage. Either way it needs to be investigated and repaired as appropriate.
Click to expand...

to form rust one needs
water & air so how much air is in the keel
 
The Lazy Kipper said:
BTW there is no deformation to the hull and no other signs of problems.
Click to expand...

I'd say you just need to keep an eye on it. If the keel encapsulation is not distorted, then I can't see there's a problem (or indeed anything you can fix). Ensure that the exterior of the keel, and the bottom of the bilge, is waterproof, so that a problem is not generated in the future.
 
Thomas Colvin is a steel man, and he says that where steel is in contact with concrete, there isn't too much to worry about - something to do with the alkalinity of the cement.

You only need to look at builder's wheelbarrows and cement mixers to know he's right. The steel rusts away everywhere - everywhere that is, except where the steel is protected by a layer of cement.

I also believe there are one or two boats around made from ferro-cement - rumour has it that those cement hulls actually get wet from seawater from time to time ... and yet their steel reinforcing doesn't rust/ expand etc. Maybe there's a reason ?
 
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What about the parts that aren't near the cement? But thinking about it I suspect this delamination as a result of rusty balast is an urban myth - in 40 years of sailing I've only ever heard about it here on the forum, never seen it, or heard of it in a yard, and neither have the guys working at the yard we are in and they are the busiest boatyard on the East Coast.
 
The Lazy Kipper said:
What about the parts that aren't near the cement? But thinking about it I suspect this delamination as a result of rusty balast is an urban myth - in 40 years of sailing I've only ever heard about it here on the forum, never seen it, or heard of it in a yard, and neither have the guys working at the yard we are in and they are the busiest boatyard on the East Coast.
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Not an urban myth - but rare. My Seawych that I built in 1977 had its steel punching ballast encapsulted in the hollow keels with resin. My back remembers it well! Boats like that often dry out on their moorings, so sacrificial keels are added to protect the bottom of the keel moulding. sold the boat in 1980 and did not see it again until 4 years ago, sat in somebody's front garden - with the starboard keel broken open. The sacrificial shoe had worn away, then the bottom of the moulding, letting water in. Bingo - exactly as predicted the steel punchings rusted, expanded and split the keel open.

The owner got the boat for next to nothing, removed all the rusty ballast with a drill, moulded a new keel (he was a GRP laminator in a local boatyard) and reballasted using the drawings and instructions I had saved from when I built the boat.

So, it is not delamination that causes the problem, but damage or wear to the GRP that lets water in and then leads to failure of the moulding.

Solution simple. Ensure the keel moulding is intact and if you dry out regularly on abrasive ground, fit a sacrificial shoe (often used on bilge keel boats).
 
electrosys said:
Thomas Colvin is a steel man, and he says that where steel is in contact with concrete, there isn't too much to worry about - something to do with the alkalinity of the cement.
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mmmmm. Not correct. Corrosion of steel reinforcement in reinforced concrete structures is a well-known problem.
I worked for a civil engineering company that made millions of pounds from treating such problems.
The corrosion condition creates an expansion of the re-bar which causes the concrete covering it to break away, a condition known as spalling.
The treatment consists of breaking out the affected areas, treating the steel and and coating with an epoxy/cement repair medium. Usually a Sika product. Tower blocks, water towers, dam structures, silos, anything built of the wonder material, reinforced concrete, is susceptible.
 
Now that the leak has been found and the area dried, what will happen to the rest of the ballast? Will the rusting process spread through the ballast? I'm really sceptical because surely the punchings etc went into the original hull at least damp - this must be true of all encapsulated ballast?
 
The Lazy Kipper said:
Now that the leak has been found and the area dried, what will happen to the rest of the ballast? Will the rusting process spread through the ballast? I'm really sceptical because surely the punchings etc went into the original hull at least damp - this must be true of all encapsulated ballast?
Click to expand...

The reaction can only go on for so long for a fixed time if there is a fixed amount of chemicals for the reaction to occur. Once the oxidisation process has converted the steel to a stable form and there is no more chemicals to use it stops. Later when water is reintroduced it starts again. If the reaction occurs and the steel is confined such that it cannot expand then stresses may be high enough to break the containment. If it can expand it may just fill the spaces and not apply stress to concrete / GRP whatever.

So if there is no water ingress and the ballast is sealed from the surface then rusting has little chance of occurring. If the ballast is dry and no water is present and open at the top of the keel then the rate of rusting will be very slow. For example I still have metal work that was formed when I was at college over 30 years ago, plain steel, stored at home, and its only lightly rusted in a few corners.
 
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The Lazy Kipper said:
We have some rusty concrete encapsulated ballast - a grounding some years ago must have left a small leak and an area about the size of a shoe box has obviously been wet. This is a dumb question, but as iron rust it expands - does that mean it will swell the keel area and cause structural problems? But having said that, there is about 5 tonnes of iron punchings, lathe scrappings and stone, all of that will surely be rusty anyway since it hardly went into the hull in 0% humidity and concrete is full of water. The iron ballast at the bottom of the keel however may not be encased in concrete - can't be 100% sure.
BTW there is no deformation to the hull and no other signs of problems.
Click to expand...

Its quite capable of splitting the grp encapsulation but it all depends on how good the concrete fill was. But you must have seen examples of rebar exploding the surrounding concrete in various marinas.

Its a problem that needs dealing with.
 
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