Ok everyone, it's that time of the year again: time to talk about concrete

I am reading this with interest as I am looking into basalt fibers and discovered basalt rod armature for ferrocement.
Rust is a problem and will eventually be a problem before this, and probably could be solve with the use of basalt armature.
I am not sure if it can be vacuum bagged for consistency, if it can be done, I imagine there would be lower labour cost than it used to.

Weight, insulation, noise and comfort are the problems remained to be solve, and I don't think it works for a sailboat which requires lightweight efficientcy, but it is a terrific way to build houseboats.

How about trawler or passagemaker type of motorsailer? Would ferrocement applicable in this case?

Probably there is no gain in cost advantage in just the construction of the hull as pages and pages of argument mentioned, but it is the easiest and viable way other than strip plank to build a one off round bilge hull.
It also didn't suffer from corrosion like steel hull and electrolysis corrosion like aluminum.
Antifouling can be applied without much prior labour and cost intensive prep unlike metal hulls, and more practical and cost effective to build one off.

Is there any examples of recent ferrocement build, successful or not that is build with basalt armature?

 

Years ago, some folks built a sailing raft out of PAPYRUS. They made it almost all the way across the Atlantic! With your "modernized" approach, why not just use some sort of treated paper?

 

Wood fibre can be used as a concrete re-inforcement, but underwater immersion, problems !

 

Nothing beyond concrete canoe competitions, from what I can tell, which is a shame, I think.

As far as I can tell, weight and cost are both significantly overestimated by the peanut gallery compared to prior generation ferroboats and current plywood boats especially. The decent ASCE concrete canoes weigh about what a commercially available aluminum canoe of the same length does. That's not very heavy, and it's a far cry from the 12 lbs/sq ft these guys seem to be remembering from the 70s. And while the hull is perhaps not the majority of the cost, it is still a very significant chunk of it. A 1 inch concrete hull (which I think is likely overkill for most of what's being discussed), equates to 1 or 2 cubic yards of concrete. That's hundreds of dollars, not thousands. Combine with 3 to 4 layers of fiberglass scrim, and you push a few thousand dollars. Just the plywood or the epoxy is easily double the total cost of materials for a concrete hull.

As far as boats which don't need to be terribly light: I'd again stress that a fully planked wooden boat is a far cry heavier than what a concrete boat would be with aluminum mast, etc. not to mention the advantages of a modern hull shape and keel. However, I was thinking the other day that a fishing boat might be an interesting use case.

That said, part of what I actually think the benefit of concrete is the possibility of cheap prototype hull shapes. Have a crazy idea for a hull? Cast it in light weight concrete. You'll sacrifice some payload, but at least you can get an idea of how it works, and then can build another one.

As far as basalt: I'm thinking of going with fiberglass initially just because it's so much cheaper. If I ever did get around to making a larger boat, the basalt might be worth the extra cost.

 

Update: I actually made a series of phone calls the other day. It took me a few before I got a guy who could actually sell me anything, but he was super interested. Lol. He sells scrim as well as GFRC premix, which might do if chasing down all the ingredients is enough of a pain, and it's any cheaper than buying the stuff online. But he also gave me two more phone numbers of guys who could source some of the other stuff. I also asked a friend of mine who works for a construction company if he could get me stuff, and he said he would check, but that the scrim and the microspheres he might not be able to get. If I have to buy microspheres online, it won't be the end of the world.

 

Isn't glass attacked by alkaline concrete ?

 

Largely because the expensive part is the binder (epoxy), not the fiber itself. Fiberglass isn't actually that expensive. But epoxy is. Also, have you worked with epoxy? It's nasty stuff. Concrete's not exactly a picnic either, but I'd rather do concrete than epoxy any day.

 

Modern fiberglass for concrete contains high amounts of zirconia, which apparently doesn't react? The short version is no, but the long version is that I think if you used regular fiberglass that you would use with epoxy, it would be. You need to use fiberglass intended for plaster. Which isn't any more expensive than normal fiberglass that I can tell.

 

I think using the canoe competition as an example would be too optimistic, ships or other boats that goes to sea for example uses more substantial armature and scantlings.

Paper rots, actually I am not too sold on the performance of ferrocement and hull construction cost and speed isn't as much a factor in the bigger picture but the possibility of easier maintanence.

Wood rots; steel corrodes, the process of sandblasting, hot-spraying zinc, epoxy coating and after a few years you have to sandblast, reepoxy and paint the ******* thing; aluminum corrodes as well and you can't paint copper antifouling on it, in ways you didn't suspect it would happen.

I understand ferrocement wasn't ideal, with all the jokes and comments aside I believe its potential is vastly underestimated and over-villified.
The point of basalt armature won't rust alone would be worth considering, you won't be worried about rusting and surveying with X-rays wouldn't be an issue, this alone would be viable in some application even without exotic fibers and additives.
I am curious if the houseboats have started to use this approach in replace of steel armature and if it is even more maintenance free than the ferrocement they are using now.

It is environment friendly, not poisonous to the workers, from the surviving examples proven to be long-lasting, not too difficult to construct despite labour intensive, different shape possible, UV resistant unlike epoxy and polyurethane, fire-resistant.
I have seen pictures of examples that it can be made to look like wood and look good too.

Besides Jay Benford, is there anyone who have design successfully for ferrocement?

 

Actually, the most successful ferro design (in my opinion) was Helsal I designed by Joe Adams and Bob Miller. But the big difference was they engaged a bridge engineer named Peter Ellen who had them post-stress the concrete with cables, allowing for a much lighter design. It won the Sydney Hobart race and was about the same weight as the boats it raced against (40 tons vs. 36 and 39 tons).

As far as the comparison with the canoes: I think it would be worth your time to read through a few of the design papers. The canoes are, to put it mildly, over-engineered. I agree that you would want to modify the structure, and possibly the hull thickness if building a bigger boat, but in terms of the mix and reinforcement, I wouldn't foresee much difference, as concrete best practices are concrete best practices. I also would say that a lot of this really needs to be evaluated experimentally. You can crunch numbers and armchair engineer all day long, but you learn a lot more from doing than speculating (I say as I continue to speculate).

 

The Helsal I I read is a 70 feet yacht, and feom the work and and post-stress involved would be much too complicated boat for us to build and use.

On Benford's board there are plans range from a 12' dinghy to a 62' trawler, of those the 35' motorsailer would be on a degree of interest and practicality, the Hartley designs and plans would look quite dated and impractical to build to me, unless there are people who have experience with any particular model they offered.

Voids can be avoided with vacuum bagging, and rusts can be avoided with basalt armature, but you still need a mold to build, unless you can form tye armature to a desired shape, some form of covering on one side and having it done and the other like how they build geodesic dome.
How do they build in ferrocement in the past?
Is mold practically a necessity?

Fishing boats are still commonly build in cement in Vietnam, but these are usually use and ditch boats with little regard to comfort and longevity, they are rough looking and left unpainted on the outside.

 

I agree about the stressed concrete

I agree, for the most part, that stressed concrete is probably more trouble than it's worth except a) most of the canoe teams use prestressed and b) there's actually a lot of expertise (and equipment) available to do it, so it might not be as bad as it seems, though again, I'd guess this would be a better thing to figure out by actually doing it and comparing.

I also agree that most of us aren't really looking to do a 73 ft mega yacht, but as far as I know, it's the only one that involved an engineer familiar with concrete in the build, and the end product was appreciably better as a result.

As far as molds go, I think the old ferro boats just used the armature instead of a mold. The canoe teams seem to pretty universally favor male molds, but I don't know if that's a limitation of the rules (I think it's mostly convenience).

For my money, I'm thinking a polystyrene mold would be nice. It's cheap, can be cut with a hot wire, and if you're in a pinch, you can actually get them pre cut by a shop that does cancelled, apparently for pretty cheap (though I don't actually know how cheap is "cheap")

 

The argument that there wasn't that much a reduction in cost is valid.
But all other materials, be it wood, steel, aluminum is difficult to maintain or have their own problems. Maybe maintainence wise ferrocement make sense with today's technoligy, and the plus side of able to be build in different shapes, cheaper for one offs.

If mold are required, it just make better sense to just build in GRP since the cost isn't that significant in the bigger picture with the benefits it bring.

 

Based on what? Have you priced materials for plywood vs. glass/epoxy? If you spend $10000 on 2 cubic yards of concrete (about what you'd need for a 1 inch, 40 ft hull), you're doin' it wrong. Look at the prices for marine plywood. Not even remotely in the same ballpark. The place you potentially don't save is in time.

 

You would use masonite on your form , bends well . Pre stress is great until it unstresses . I would use carbon rebar in my stringers , and carbon tape . We had to beef up a large footer once and , carbon tape with epoxy was the fix .