Ferro Cement Hulls ?

[Alan Wheeler]

I can quote you some info from Colin Brookes book, or I suggest you order it. It is still available and not expensive. It covers over a life time of FC building and the one huge advantage of being able to look back and see what worked and what didn't over that time. It goes into great detail an all aspects of the construction, including what is required and how to set up the site and equipment for plastering day.
A couple of key points. The use of Bird netting, NOT chicken wire. The bird netting has a smaller hexagonal shaped hole. Chicken wire is much to large. NOT welded mesh.
The welded truss method is far stronger. A little more time consuming, but very strong.
If you or anyone has a particular question, just ask and I will quote from his text. But I do suggest you get the book, it is tremendousely worth it.

[Capall Ban]

I have Colin Brookes book and have read it back to front (and the other way around) several times ,but I've also researched other reputable sources which favour weld mesh
although I'm sure that netting would be much easier to fair.Iwill be building with trussed frames and trussed stern/keel/stem.I have to say that I'm leaning towards weld mesh at the moment.

[Boracay]

I built a Hartley RORC 32' some years ago so if I can be of assistance please ask.
I could probably give better answers if I knew the design and where you are building and the condition of the building site.
I am not aware of any long term difference between using weld mash and hex wire mesh. I used galvanised hex wire mesh. The weld mesh probably gives a greater density of steel, but the wire mesh would be easier to work with and give more zinc on the wire.
I used hard drawn steel rod for the stringers. I don't know if the book still recomends it. I felt that it gave a much fairer hull.
Other key questions that you need to answer at this stage are about the ballast, the waterproofing of the cement, the sand and the cement itself.
I queeried Richard Hartley about using modern waterproofing when I was about to plaster and his reply was that you don't polute your lungs with smoke and you don't use modern waterproofing. He recomended the use of pozzolan, which I think is the same material the Romans used in their cement. I found an internet reference here :- http://www.westernpozzolan.com/
As you watch your hull cure you will see the an interesting interplay between the components, particularly with regard to the microcracking that occurs with cement. I believe that pozzolan is a key part of that interplay, and that the interplay will continue for the life of the boat.
I used a mixture of boiler punchings and cement as ballast. This was the worst mistake I made with the boat although it was common practice at the time. The boat was stable enough, but when hit by a gust it would develop major weather helm. I cannot recomend strongly enough the use of solid lead ignots, properly isolated with a suitable coating, deep down in the keel, and properly secured.
You will need to use clean fresh cement of the type recomended by the designer. It is essential that the cement be fresh.
The sand must be clean, sharp silica (river?) sand with a particle size recomended by the designer. Some of the reports that I have seen of total disasters have related to use of unclean sand, particularly that contaminated with salt. The use of coral sand may render the hull useless.
I would urge you to reconsider the use of ferro for the hull only. I built a ferro hull and deck and felt that it gave a substantial increase in structural rigidity. Some care is necesary (waterproofed wooden struts to hold up the deck between frames to prevent sagging) to ensure a thin deck but in the end I feel that it is worth the effort.
I would also urge you to reconsider plastering the hull in one shot. It is difficult for even a skilled plasterer to ensure that there are no voids in the hull with single shot plastering. Two shot plastering almost guarantees a solid hull, and the use of clean fresh cement, sand and pozzolan will help to make sure there is a good bond between plasters.
When I did my boat the plasterers used slightly wet cement which pushed through the mesh and protruded slightly on the other side causing knobs all over the inside. I consulted Richard Hartley on this and he advised me to take a "scrutch cone" (stone masons chisel) and to cut them all off. Not a pleasant job but worth it in the end, as I ended up with a three quarter inch hull.
As a side comment here a friend finished off a 34' hull, no deck, that he brought that had been plastered single shot. He sailed the boat to Europe, and along the French canals untill one day he touched a solid wooden post and the side of his boat caved in!
If my memory serves me well it took me about 500 hours of very part time work to get the hull ready for plastering. That does not include head scratching time.
The first shot of my plastering took four skilled plasterers one very long day (from memory). I would strongly urge you to use skilled plasterers. They will give you a much nicer hull.
The second shot took (my memory is hazy) three men less than a day, and the third (to finish off the deck) only a few hours.
This all happened quite a few years ago, alcohol was involved. My memory may not be reliable.
The other thing that you can do that will shorten your building time is to make special plugs for where ever a hole is needed in the hull, for example through hulls, prop shaft, rudder shaft and holes for bulkhead, chainplate and stanchion bolts. The plugs will need to be protected to prevent them from leaching water from the cement during cure. You begin to appreciate just how tough ferro cement is when you have to get inside the hull and drill lots of holes in it.
My final recomendation is that as you build the armature you frequently take the time to step back and check the hull for fairness. If you have a friend with a good eye ask for their opinion.

[Matt Hager]

I spent 5 months in Mexico in a boatyard working on a FC 120" Ketch. It was built in 1974. After we scraped(with a torch) the paint off and got the hull material. I was suprised to see good of condition the hull was in. We repaired about 5 spots each about 3 feet square. When we got to the rebar and wire mesh they looked like they where new, no rust no corrosion of any type. As the captian said FC bleeds it does not leak (his second FC boat). I was impressed with the strength of the hull and how well it held up. I was showed pictures of 65' FC boat they worked on for some research foundation and the intire port side had been repaired and replaced. that boat had over 300,000 NM on it.

Second story. I had my boat in a boatyard in Ruskin Florida doing a bottom job and buffing out the hull (lots of work) I meet a gent that had a 45' FC ketch rig that had the bow smashed up from being pounded into a concret pier his boat was tied to during on of last years hurricains. He stated that the boat was pounding on that pier for over 15 hours before they could get to it. I supprised how little damage it had for such a pounding.

All I can tell you is that the 2 boats I have seen in the boat yard the material is strong and will take a pounding.

goodluck,

matt

[Capall Ban]

Greg/Chris,
The design is an atkin 34' double ender disp. 21000lbs.It was designed as a gaff ketch but I'll be rigging mine as a pole masted gaff cutter circa 700sqft. working sail.This gives me a main of about 340sqft which I should manage without too much bother alone if the need arises.An aluminium gaff is a possibility I m also contemplating.The stations on the lines plan are 29' apart which is just about right for my truss frames.I know that several of atkins "eric" 32'1" 19500lbs have been successfully built in ferro retaining their designed ballast disp ratio.For ballast I plan on using lead ingots sealed in epoxy and cast in the keel after launch.(a 33' colin archer launched with a 5/8" ferro hull in england several years ago couldn't fit enough ballast below her floors to bring her down to her marks.It is possible to build a ferro hull too lightly).Pozzolan sounds like good tack.I'll be using 5 pro plasterers to finish, 5 semi skilled ahead of them applying muck and 4 skilled labourers mixing with one supervisor.10 serfs will do the hauling of buckets and I'll be floating around the edges having a nervous breakdown.Only the hull will be ferro.The rest will be built as a traditional yacht would be(I'm a carpenter).The building frame will be erected alongside my cottage and covered with poly on hull completion to provide shelter while fitting out.And Matt I share your faith in the strenght of well built ferro.You lads are the first people I've "spoken" to who have built ferro boats.It's nice to hear something positive about my choice of hull material and to finally speak to people with practical experience of it.

[Boracay]

Sounds like you have everthing under control.
One last point. The building frame for a ferro yacht ends up with all sorts of bits sticking out at about eye level.
Please watch out for them, mark and reduce them as necessary and watch out for other hazzards.
Good building.

[Capall Ban]

Yeah...thats the plan ..I can't wait to see what really happens!!!
I'll let ye know when i start..

[Boracay]

Design chosen, building site lined up, partner permission, surely you have already started!
Now, just a little bit every day....


I have posted a picture at :- http://cruisersforum.com/photopost//...php?photo=1557
so you can see what happens to old boatbuilders.

[glenville]

I have recently acquired a 37' ferrocement endurance that fell over from its stands breaking off
the bowsprit and tip of the bow and causing two large indended areas and a crack (aprox. 1/2 cm diam.
and 3-4ft. long) on the starboard. I've done lots of reading and recently purchased Colin Brookes book. My questions are mainly about materials to use for repair. Brookes book references
fer-a-lite . I've spoken to the people that sell the product and reviewed it in Bingham's textbook.
It seems like a good product and am wondering if anyone has had experience with it and could make any
recommendations.


My repairs are obviously large and from what I understand from Brookes book you would recommend either
epoxy mortar or plaster mix and a bonding agent. If I used west epoxy what are the ratios of cement
and fine silicon sand that I add after the resin and hardner have been mixed? How fine should the silicon sand be?
If I use a plaster mix if I understand the book right I mix two parts portland cement to one part sand plus
water putting white glue on the edge of the old concrete just before appling the new concrete.


thanks for the help

Mark Bennett Nova Scotia, Canda bennettm@cbdha.nshealth.ca

[CaptainK]

Hey glenville.

How's that ferro hull coming along?

I am a fan of ferro's. Yeah there's been a big bashing against ferro-cement boats here in the U.S. .

Eventhough, I did persue that thought when I first joined this forum. And still have certain interests, in ferro-cement boats.

I wish you luck in getting the damage repaired. As soon as possible. Good luck!!


Kevin

[encore]

Mark,

That's a pretty large crack. Does the armature look like it is intact? If the armature is good, from what I have learned on my boat, I would clean out the crack, coat it with epoxy and when it gets tacky, fill it with a mixture of epoxy and portland, about as thick as you can mix it. It bonds well and seem to hold up, although mine hasn't stood "the test of time." You can also add a small amount of fine sand if you wish. If the armature is damaged, you have a structure problem and a completely different issue.

A good bonding agent if you choose to go cement, is acrylic that is sold at home building supplies. You can coat with it first and then mix the agent with the portland instead of water. (Acrylibond)

With that large a crack you should be able to go in and expose the wire and then force the filler in and around it.

Colin Brooks at ferroboats.com is the authority and he responds very quickly to e-mails. His book available from the site and is an excellent guide.

Sam Cowles at ramprasaduk@yahoo.co.uk is also very helpful. He is usually cruising but returns e-mails. He has made many transatlantic crossings in the boat that he rebuilt. It's an interesting read on his web site.

Good luck, Ellis

[encore]

Mark,

There is another excellent bonding agent that is used between old and new concrete. It's called Concresive Liquid LPL and it has been around since the early 80s and is now used in the building industry. It is a long pot life (LPL) epoxy that gives you about six hours to work. My dealer (Brock White) said that you could add sand to the mixture and fill up to about a quarter inch. Information is available at www.DegussaBuildingSystems.com

It comes in gallon mixes and once opened the entire contents must be used in fairly short time. If I remember right it is about $70 a gallon.

Ellis

[glenville]

Thanks for all the input lots of great info.

I had recieved email reponses to questions from the nice fellow at ramprasaduk@yahoo.co.uk . He had used a product called ronocrete to connect old to new concrete. Colin Brookes responded very quickly to emails. He advocates the use of white glue to connect old to new(I just can't quite get
comfortable with the glue idea). He certainly has got lots of examples where its been used with good results.

I guess I'll have to make a decision as to which bonding agent to use.

The bonding agent has raised another concern. I have read some in the ferrocement.net forum about concerns with different material mixes. Specifically if the type of cement and mixture of sand were different than the original manufacturing stuff the new and old cement may have different physical properties. This may cause a
high stress point leading to structural
cracks. I don't know the original mixture. Do I just use standard mixtures? Using the same logic I'm wondering if the white glue is the best as certainly epoxy bonders are of highly different than cement. Anyone have any thoughts. Maybe I'm overthinking it.

I guess nobody has heard of feralite.

In Nova Scotia theres not much weather to be working on the sailboat. Currently I'm trying to get axles under the craddle to move the boat into the barn. I hope to have the boat moved within a couple of months and hope to plaster sometime in the summer.

Again thanks for all of the input. Any further comments are much appreciated.

Mark

[Alan Wheeler]

Firstly, you can trust Colins advice. He is THE authority in FC.
Secondly, don't think of the PVA as a glue in this matter. In fact, it's why I am a little nervouse when anyone starts suggesting epoxies and other adhesives. You ARE NOT glueing the concrete together. It could never work, it simply wouldn't be strong enough. PVA becomes a chemical bonding agent of two dissimilar concretes. The cement becomes part of the PVA, becuase the PVA is also water based. PVA Glue is no different to the commercial bonding agents you would buy in a hardware store for that purpose. I imagine products like Ronocrete are the same stuff, different recipe. PVA has been used under many different names for many years. You just pay an aweful lot more for the stuff with the fancy name on it.
As for the difference in cement and aggregate. Don't get too hung up on that either. Just as long as you use the right stuff and in the right mix ratio. You just have to assume that the original builder used materials to spec as well.
And finally, yes epoxy expands and contracts at a different rate than Concrete. So it is best to use Epoxy to a minimum. It is fine for small repairs and fills, but nothing major and NEVER glue anything down to the deck or hull with epoxy. It will eventually break a Chunk of cement right out or the surface, but remain thoroughly stuck to the item you stuck down.

[Boracay]

My concern with your repair would be to ensure that the hull had sufficient structural integrity both before and after the repair.
Have you checked for damage prior to the accident? I would expect that there must be some pre existing damage, if only because of the age of the boat.
Ferro Cement design is by its nature a less than exact science so there may be design issues that could be addressed when doing a large repair. By the same token if you look carefully you will probably find areas where the construction was less than perfect. Look all over for fine cracks, particularly in areas that are stress risers.
If the bowsprit broke off this may suggest that it was not properly attached initially and this may need to be an issue to be addressed.
The large indented areas are what I would have expected if a heavy ferro boat fell onto its side. My understanding would be that these would need to have all damaged cement "gently" removed, the mesh and reinforcing rods refaired and repaired as necessary, and then the whole area replastered. I believe that it would be wise to check this with Colin Brookes.
My main concern would be with a 0.5 cm wide and 3-4 ft long crack. A crack of this size may indicate that the underlying reinforcement has stretched, or that the cement has come away from the reinforcement. It could also suggest that the may be underlying construction and/or design issues that should be checked. It may be wise to consult with Colin Brookes about the possibility of checking this.
The other point that I would like to make is that cement is, of course, very weak in tension, the tension loads being taken by the reinforcing. I think that those who have suggested the use of a cement sand mix have made a valid point. To that I would add that pozzolan (or if you can determine what waterproofing material was added to the cement then that material could be used) could be added to the mix in the recomended manner, and that the resultant repair could be kept wet for the recomended time, as would have been done with the original boat.
If you do the repair with sand/cement/waterproofing agent then it may be wise to recoat the whole area with a matching epoxy after the cement has cured.
My memory has grown hazy with age but I seem to remember that fer-a-lite was a form of light weight cement. If your boat was not built with fer-a-lite originally then it may not be wise to use two different materials in the repair.
Before replastering it may be wise to check that here is no powdery residue on the original intact cement.
I have assumed in my comments that your boat was built in the conventional manner, that is a suitable sand cement plaster with waterproofing agent was forced through a wire armature in the single shot or two shot method. After curing it may have been coated with some sort of epoxy paint or resin. If your boat was not built in this way then my comments have little value.
As the repair that you are undertaking is major I would, of course, suggest that it be carefully tested over an extended period of time.