Ferro Cement for Dreamers

[Old fella]

I bet all the negitive comments are from people who have never owned one, and yet they're experts, over yhe years I've owned 2 of them along with boats of most other constructions, give me ferro any day, if it wasn't for idiot uniformed insurance companies I'd have another one. I have to say home built ones I'm not sure about, but here in NZ I like the ones built by Ron Sayers or auckland ferro company

[Simi 60]

Originally Posted by NevilleCat

Ferro cement houses were a bit of a passing fad around the same era. Some quite stunning places built but definitely "outside the box" (think Hobbitown).
As ferrocement gains its strength from the curves then this led to curvey designs. I have seen a doco on a famous place in the hills in California and right down to home built off the grid construction in an isolated area in Asia. Try searching on youtube etc.
Anyway just giving the thread a bump...I know it's a drift, but hoping someone might be able to point you in the direction of books or other resources.

This was fairly close to where I lived as a kid.



https://www.museumofbrisbane.com.au/...es-space-city/

[Nani Kai]

Originally Posted by senormechanico

Might be worth it if you need an artificial reef or floating breakwater.


Concrete Ships: The Powell River Floating Breakwater

For what it's worth, ferro-cement hulls make excellent artificial reefs. We sunk one in Hawaii when I worked for a dive shop there in the '80's. It's now a great lobster spot and provides habitat for all manner of marine flora and fauna. If it's only a hull, with nothing yet added that would create environmental issues, it could be a great dive wreck and artificial reef. Jes' sayin'.

[AmberSands]

I’ve owned a Samson 40 C-Spirit for the last 5 years in the UK. I was wary at first on buying her but I wouldn’t swap her for a grp. Yes you can’t sail in a F3 but when the other yachts are bouncing around and heading for home we’re as stable as anything. We sail in the Irish Sea and it’s more often than not bumpy. We have fully comp insurance for anywhere in our waters.

We bought her thinking it was a cheap investment but new sails on a Ferro cost the same as new sails on a GRP. So don’t think it’s cheaper because it isn’t.

We learned to sail on her in congested waterways with strong tides (Liverpool). For me I’d have a look at the boat as 57’ is a lot of boat.

[AmberSands]

[ATTACH]

[bobnlesley]

I've never owned or sailed a ferro yacht, but I was aboard one for a beer just a few days ago - lovely boat, commercially built in NZ, sadly I can't remember the make, too many beers? - and a comment the owner made that evening would apply very well to the Ad in the OP: "Afloat since 1975".
What the NZ owner said was; "It's much easier/safer to buy a ferro cement boat now than it was twenty years ago, because most of them are 30+ years old, so if they're still afloat now, then they must've been built right in the first place."

[AmberSands]

Yes you’re right. I met a senior construction engineer last year on the marina. He told me they take 50 years to properly set and 50 years to deteriorate.

Ours was built 1972. And she’s been across the Atlantic twice. Great boat. I love her.

[wharfbanger]

Dear All,

I just bought a ferro sail boat in Auckland and hoping for advice on a small weep coming through to the inside of the hull below water line, along the centreline between the chain locker and the keel. It is a small amount of rusty coloured, acidic tasting water. Enough seepage to wet a single square of toilet paper in a couple of hours. Suspect micro cracking or porosity allowing seawater through. Boat was built in 1969 and is otherwise in great shape with no rust stains interior or or exterior.

Any thoughts?

[skipperpete]

Despite the blizzard of negativity you’re probably going to get, I’ll try to answer your question. Yes you can fix but it means a haulout and a lot of crappy hard work. Start at the weep and strip back the cement until you find the armature, my guess is that the ferro has corroded and expanded creating micro cracking and more water intrusion so its important to find the limits of the cracking, replace the baddest of the armature and re plaster with one of the better cement additives. I’ve only been in shipyards where this type of repair has been done on neighbouring boats, not done this myself so perhaps an actual do-er will weigh in with hands on advice. I know for sure it can be done, and don’t be surprised if the removal part extends further than imagined, it will probably be a square foot, maybe more.

[billgewater]

re repairs on ferro-cement boats.. Yes. Some were badly built - particularly some of the Samson vessels. Corrosion of the steel armature can be very local or it can spread. It depends on a number of factors. Internal rust bleeding usually is a sign that at least, locally, the reinforcing has had its day and the area needs to be broken out. Whatever the area, you should break out material until you have found good mesh and reinforcing.
The repair process can involve basically two methods Both use epoxies mainly because using cement requires long (30 day) curing cycles then drying before painting - all which costs a small fortune in most boat yards.
The first method requires that you rebuild all the mesh and reinforcing, ensuring good overlap and joining of the main rods (welding). I have seen main rods being replaced with high tensile threaded bar. This gives greater surface area for improved adhesion to the bulk material. You then use an epoxy which can be pushed all the way through. If you do this use something like the 5:1 resins with a slow hardener. You can add sand for bulking (only if it has been dried - important) and you can also add thixotropic agents that reduce the fluid/runny nature of the resin mix (Q cells works). Sand may assist in moving the thermal expansion properties of the repair closer to that of the original cement matrix but this probably is not an issue except for large areas. You may also need some "formwork" to prevent the resin mix from running out. At the junction of the resin mix to the old concrete it pays to wet out the join area with neat resin mix on a brush. This may require that the surface mesh layers be able to be folded back adjacent to the join area. Using a slow hardener should allow time to reset the surface mesh in place.
Make sure that the new mesh does not protrude past the original level. You need resin cover over the mesh to protect it against further rust.
A good trick is to finally paint or trowel on a thixotropic layer of about 3 to 5 mm of resin mix without sand, which allows easy sanding and fairing and adhesion of an epoxy primer paint prior to antifouling etc.
The second method is to consider using glass fibre and epoxy. Do not use anything but pure laminating epoxies. Never use polyester resins. Polyester adhesion is extremely poor.
This second method requires some chamfering or bevelling of the old material at the edges to allow a reasonable length (5 to 10 cm) for the joining of resin wetted glass to the old ferro. Some serious angle grinding here.
This method does require some "formwork" and here is what I have done at least once. The plan was to apply the resin and cloth from the inside, so I made a cardboard outer mould and used tape to stick it in place on the hull outside. Prior to sticking it on, I screeded about 3 mm of resin and Q cells onto it as a sand-able surface later. Then I laid fibre glass tape from the inside. I used a combination of tape and random directional glass. Beware that if it is done too quickly, it can get very hot. Slow set resins have time to allow the heat to leave steadily. Fast set resins less so.
Make sure you ensure all resin mixes are done accurately and that you wear proper protective gloves etc.
Both methods can work well. What you do will largely depend on the gradient of the repair area and its size.
I assisted with a rather large area (over 1 m square) that rose up vertically from the keel and then curved overhead. We used the first method with sand and Q cells but our mix was initially not thixotropic (stiff) enough and kept creeping down and out, so we scrapped off the mix until it stopped coming out, added more Q cells and repeated the process over the same area. After the resin started to go off we attacked the whole area from the inside with the resin/sand and Q cell mix.
Ferro repairs can be done and in some cases is cheaper and easier than for steel boats. I have seen fibre glass boats suffer from osmosis to the extent that the boat was a complete write off. Ferro repairs just require a bit more thought and planning.
The most dramatic ferro "repair" job I saw was on a boat that showed some blistering and it was sand blasted to clean cement and then Dynel covered. Dynel is a flexible cloth that adopts to compound shapes and uses laminating epoxy resin. An expensive process as it uses a lot of resin, but from what I heard, that boat is still around.

[skipperpete]

Originally Posted by billgewater

I understand that that the oldest floating boat is a ferro cement boat built around 1837 by George Lambot in France. It is a material that if built properly (and that's the issue often), does not rust nor does it burn.

I have seen a ferro boat that had a major gas started fire on board and it completely gutted the boat. The hull survived without any issues and the vessel was re furnished.
Try that with a glass or metal boat.

We make bridges and multi story buildings from steel reinforced cement don't we?

I’ve also seen a ferrocement boat (here in Australia) that had a fire on board that would have completely destroyed a grp or timber boat, he rebuilt the interior.... and she was still the most beautiful schooner I’ve ever seen, totally impossible to see that she was ferrocement and sailed beautifully...... Alden design.

[Mickeyrouse]

I recall when I was first getting my toes wet in sailing that there was a lot of buzz in the sailing press about ferro. The mirage-like attraction of low cost lured a lotta guys in that direction. But the pencil-pushers got to pushing pencils and determined that the cost of materials for the hull of a finished boat was something like 6-8% in the forty-foot range, and the percentage decreased with the increased hull length. And as I recall- I’ve never sailed in one- the handling, motion, etc. didn’t start to get reasonable until about 35 feet or so. There seemed to be kinda narrow range of suitable size.
I have seen a couple ferro boats over the years that seemed to have been constructed with skill. But I’ve seen too many ferro boats that were bleeding rust streaks. Cosmetic? Structural? Who will ever know except the hard way?
In the end, it took just as much skill to build a good one as it did a good plank-on-frame wooden boat. But with much less enduring appeal.
There used to an old warehouse or something north of Morro Bay in California just off the highway that had a yard full of abandoned double-ender ferro projects. Reminded me of an elephant graveyard.

[Bowdrie]

Originally Posted by Mickeyrouse

I have seen a couple ferro boats over the years that seemed to have been constructed with skill. But I’ve seen too many ferro boats that were bleeding rust streaks.

Same here, seen a few good ones, (a couple of really good ones,) and a bunch of, shall we say, inferior ones.
There was a learning curve that's for sure.
It was important to use a well-blended mix of grain sizes for the sand, and it needed to be a very clean/washed product.
It was found that the lime reaction would form microscopic gas bubbles around the galvanizing on the mesh, this precluded the intimate contact needed for the best bonding and over time would lead to rust.
The answer was simple, a relatively small amount of Pozzolan added to the cement stopped the reaction and tightened the bond, and this also prevented much of the rust forming that works to start the minute surface cracks that show as rust bleeds, (the armature is close under the surface).
As might be expected the best quality of Portland hydraulic cement mixed quite rich gave good results, that and clean/pure water without chlorine.

[longjonsilver]

i built a ferrocement boat back in the 70's. i got the idea from a yard of do it yourselfers building Samson designs right between Hopkins Marine Station and the "new" Monterey Bay Aquarium (was an abandoned cannery then). The use of Pozzolan clay is a good idea. The square welded mesh is superior to chicken wire or expanded metal. Spring steel rods are a good idea. Anyone saying you need 2" (50mm) of cement cover doesn't understand ferrocememt. This is not ready mix you get out of a truck. (i have poured 1000's of yards of ready mix in industrial buildings for slabs, tilt ups and footings) The mix for a boat has to be carefully designed and mixed accurately to get a good boat. The mix uses LOTS of cement, and if not reinforced minutely like in a ferro boat, wud crack all up. Like stated before the sand must be clean and properly sorted for size. i used Monterey sand from the old sand plant in Pebble Beach - now a resort hotel. It is true that the larger the boat the better for ferro, altho i have seen canoes made of ferro, they looked WAY overweight. A fat short boat like Colin Archers "Eric" is about the minimum size imho. Benford designed some real pretty retro looking boats in ferro. He also wrote a book about ferro that might still be available. i bet you can buy ferro books on Amazon.

[MicHughV]

As pointed out above, rust can be insidious. Finding it inside your hull is only the " tell tale" of a likely bigger problem.

I'm speaking as a structural engineer here.
Steel, when it rusts, also expands, and as it expands it will cause sufficient pressure to pop concrete apart.

Seeing rust in one spot does not mean the rust originated there, it could have wicked along a strand of rebar from elsewhere.
Then we come to concrete. Concrete can made from a variety of different formula's, mixes and additives and getting it delivered on time from the batch plant is critical. This applies generally to large quantities.
It won't do to run down to your local hardware store to pick up a bag of cement and make your own unless you really know what you are doing.

Finally, providing sufficient "cover" is important for two big reasons.
1) Reinforced concrete is steel and cement working in tandem with each other. Steel providing tensile strength and concrete providing compressive strength. This is an exact science and it's use is well documented and understood.
2) "cover" is the "distance" between the steel and the outer edge of the concrete. On a ferro cement hull this means both sides of the hull. Here again, this is a precise science. "cover" also provides protection, ie, a barrier over the steel, preventing water from getting near the steel to promote rust. Within constraints here, ie, weight, thicker is always better.

Finally, "patching" concrete means adding new concrete to existing concrete, which comes with it's own set of requirements as the two parts need to be " glued together" so to speak.

Then one must ask how did this occurrence happen in the first place.
Was it an impact with something ? Bad design ? Poor workmanship?? etc, etc.

Having thus explained some stuff. It is possible these days to purchase cement in " pre-mixed" bags depending on the purpose it is used for.
Besides the "bag" option it can also come in a standard "caulking" gun type of application, where the product is simply pumped out without having to do much thinking.

Here is where I'd recommend spending some time on the internet to learn what is the best likely product to use for your particular problem. There are several excellent products available for just such a need.

So, yes, a haulout is in your future here. The problem you have discovered is only going to get worse without attention

Before you start hacking away at your hull, get more informed and then be well prepared when you do.

Wishing you the best.