Rusty ferrocement

[Hairyloon]

I've been considering getting a boat. One of the ones I was looking at is an unfinished ferrocement project and in a couple of places I can see the beginnings of rust in the steel rods.

My thinking is that if the water can get to the steel, then the rust will expand and crack off the plaster.

Or it may be just a bit that rusted during construction and is now stable.

 

My experience of ferrocement is almost zero, so any advice anyone?

[carlt]

I've been considering getting a boat. One of the ones I was looking at is an unfinished ferrocement project and in a couple of places I can see the beginnings of rust in the steel rods.

My thinking is that if the water can get to the steel, then the rust will expand and crack off the plaster.

Or it may be just a bit that rusted during construction and is now stable.

 

My experience of ferrocement is almost zero, so any advice anyone?

Steer clear, would be my advice.

 

Your thinking is spot on and there isn't really any way back, once the concrete starts to separate from the reinforcement.

 

I do know someone who forced more cement, into the cracks, but I think he just delayed the inevitabe.

 

Of course, if you can see the rods, then they're exposed to the atmosphere and that bit would corrode anyway, but can you tell whats going on underneath?

[ChrisPy]

Light rust on reinforcing steel is not a problem, in fact it increase the bond between the steel and the concrete. The lime in concrete naturally protects the steel against further corrosion under normal circumstances - that is why it is common practice to apply limewash to the inside of water tanks.

 

If you see a reinforcing steel cage in a building before concreting which is not rusty, it is probably because the steel is covered in dark-grey millscale. Unless the cage has been specially treated this will fall off in a short time, and the steel will rust. Light rust is not considered to be a problem. Rust is not a disease of the steel: if the conditions are not right, then further rusting will not occur. By the same token, non-rusty steel embedded in cement/concrete will soon rust if the conditions allow (eg cracks and sea water).

 

So it is vitally important that there are no surface cracks that would allow water (especially sea water) to migrate to the steel, where the salt content will negate the lime protection and cause accelerated corrosion. Ferrocement boats should be well sealed with appropriate paint coatings to avoid this.

 

In aggressive environments it is common practice to apply cathodic protection to the reinforcing steel - the same should be possible for boats.

 

If you inherit a steel armature ready for 'plastering' you can always gritblast it or wirebrush it to remove heavy rust, but of course the light rust will immediately appear again before you can enclose the steel in plaster.

 

If you need further in-depth advice there are some very good books on the subject. Hartley's of New Zealand is a good source of information and advice.

[badgerburger]

Hi, HairyLoon. How about posting some pictures - especially close-up of the rust?

 

Also, does anyone know how to tell whether ferrocement has surface cracks, or should these be obvious ??

 

BB

[ChrisPy]

Also, does anyone know how to tell whether ferrocement has surface cracks, or should these be obvious ??

I would assume it has (even just micro-cracks) and treat the surface with a very good coating. Google for 'ferrocement surface painting' will give lots of information.

[Malarky]

I think you'll find Ferro-cement unpopular, as the science involved is just not beautifull compared to, say wood, but steel, although not as scary is pretty horrid too, despite all it's beauty. This could make this boat extremely cheep if you tune in to all the bad points with cement boating!

 

To add to Chris's comments, the rust can also act to "grease" any movement due to the diffrence in expansion rates of steel and the cement, which, incidently has the same rate as glass..

 

I,m intrigued, is it a narrowboat? Would be great to see some pic's. Ever thought of building one?

[ChrisPy]

The best ferro boats are 'shapely' - they derive much strength form the spherical 'eggshell' shaped surfaces - which is why it is often used for blue water cruising yachts and fishing boats, where the cost of fabricating a decent shaped steel or timber hull is significant.

 

It is not suited to narrowboat construction, which is all flat surfaces, and where welding steel plates together gives a relatively cheap product that can stand the knocks (because it is resilient) without needing excessive framing. A dent in a steel hull can be tolerated, a dent in a ferro hull has broken the structure and needs extensive repair.

[Malarky]

The best ferro boats are 'shapely' - they derive much strength form the spherical 'eggshell' shaped surfaces - which is why it is often used for blue water cruising yachts and fishing boats, where the cost of fabricating a decent shaped steel or timber hull is significant.

 

It is not suited to narrowboat construction, which is all flat surfaces, and where welding steel plates together gives a relatively cheap product that can stand the knocks (because it is resilient) without needing excessive framing. A dent in a steel hull can be tolerated, a dent in a ferro hull has broken the structure and needs extensive repair.

 

This may help explain why I've never seen one, and after hearing about a fero-cement narrow boat, several years ago, it has been niggleing me as how to sensibly build such a thing! I suppose I was "had" there then!

[Hairyloon]

Thanks for the input.

Since you ask:

I don't have a close up of the areas of concern, I may go back for another look.

I couldn't see any visible cracks, but I didn't look very closely, I'd already got scared by the size of the project and was about to run away.

Have recently been rethinking.

And yes, I have thought about building one, I don't know how, but I do have potential use of a boathouse, but the only practical way to get to the boathouse is by boat...

Edited February 23, 2008 by Hairyloon

[ChrisPy]

nice shapely hull, but out of place on inland waterways, I think.

[carlt]

This may help explain why I've never seen one, and after hearing about a fero-cement narrow boat, several years ago, it has been niggleing me as how to sensibly build such a thing! I suppose I was "had" there then!

Concoform, at weedon, built them, in the 70s and a chap near Nottingham (who's name escapes me).

 

There are still a few about, there's one in quite good nick at Sutton stop, and one, in not such good nick (I think the wooden top deteriorated and collapsed) which gets dragged around the Oxford by someone who can't bring himself to leave it.

[Hairyloon]

nice shapely hull, but out of place on inland waterways, I think.

'salright, it's on the yard.

[denboy]

there used to be one in excelent condition moored at cranfleet dont know if its still there

[mikeys]

Concoform, at weedon, built them, in the 70s and a chap near Nottingham (who's name escapes me).

 

There are still a few about, there's one in quite good nick at Sutton stop, and one, in not such good nick (I think the wooden top deteriorated and collapsed) which gets dragged around the Oxford by someone who can't bring himself to leave it.

 

carlt

must have been sometime ago you saw my ferro boat at sutton stop its been at rugby for last eight years looking very good fitted out now

reading other comments on ferro mine is forty five foot long and is powerd by lister sr2 engine

[carlt]

I'm in Rugby. I'll wander up and have a nosey, sometime.

[Guest TerryL]

I've been considering getting a boat. One of the ones I was looking at is an unfinished ferrocement project and in a couple of places I can see the beginnings of rust in the steel rods.

My thinking is that if the water can get to the steel, then the rust will expand and crack off the plaster.

Or it may be just a bit that rusted during construction and is now stable.

 

My experience of ferrocement is almost zero, so any advice anyone?

 

I've got a professionally built to Loyds spec ferro motorsailer, I'm very pleased with it. Are the exposed rods inside? If so they just need painting but there shouldn't be any showing outside.

[mikeys]

I'm in Rugby. I'll wander up and have a nosey, sometime.

 

No problem here most of time doing somthing, the boatbuilder you were on about from nottingham was Davidsons they built six in late 60s

of which mine is one of them the hulls all came from Poole and they did fit out they all then went onto the broads as hire boats this according to

a guy that worked for them and saw mine while still at sutton any look forward to seeing you

[pirate paul]

I've been considering getting a boat. One of the ones I was looking at is an unfinished ferrocement project and in a couple of places I can see the beginnings of rust in the steel rods.

My thinking is that if the water can get to the steel, then the rust will expand and crack off the plaster.

Or it may be just a bit that rusted during construction and is now stable.

 

My experience of ferrocement is almost zero, so any advice anyone?

 

 

Hi I am looking for a very cheap ferro boat, if your not interested in this vessil I am... any chance of a contact email or number.

Tar & stuff

[ThePiglet]

It's probably sunk by now

Edited July 24, 2009 by ThePiglet

[nb Innisfree]

No problem here most of time doing somthing, the boatbuilder you were on about from nottingham was Davidsons they built six in late 60s

of which mine is one of them the hulls all came from Poole and they did fit out they all then went onto the broads as hire boats this according to

a guy that worked for them and saw mine while still at sutton any look forward to seeing you

 

 

I think the world's first concrete boat was built at Poole about 1905, quite a big one. Built near to or on the site of Sunseeker if I recall correctly.

[pirate paul]

The best ferro boats are 'shapely' - they derive much strength form the spherical 'eggshell' shaped surfaces - which is why it is often used for blue water cruising yachts and fishing boats, where the cost of fabricating a decent shaped steel or timber hull is significant.

 

It is not suited to narrowboat construction, which is all flat surfaces, and where welding steel plates together gives a relatively cheap product that can stand the knocks (because it is resilient) without needing excessive framing. A dent in a steel hull can be tolerated, a dent in a ferro hull has broken the structure and needs extensive repair.

There was a ferro barge at Portsmouth, opposit the old submarine and ship scrapyard......That was about 4 or 5 years ago. 100ft or so!

[carlt]

I think the world's first concrete boat was built at Poole about 1905, quite a big one. Built near to or on the site of Sunseeker if I recall correctly.

Sorry, but I'm sure it was a French invention, mid 19th century, iirc.

 

 

Edited to say: Yep, Google tells me it was Joseph-Luis Lambot, in 1847.

Edited July 26, 2009 by carlt

[Greybeard]

I'd never really heard of ferro boats before so this is an interesting subject - I think I've actually spotted one under a tarpaulin in a farmers field.

 

I'm going to check it out to find out for sure.

 

As an aside http://www.concretesubmarine.com/ looks interesting.

 

Wouldn't get far up the T&M though!

 

Mike