Thanks for your comments Arne. An extremely thin-shell cement boat reinforced with basalt using random fibres and/or mesh would probably require a female mound, or, as you say, be deployed as a sheath over an existing hull. However I would not discount the possibility of a more conventional layup over a cheap system of temporary frames and stringers – or permanent truss frames as per the Hartley boats, which were popular in New Zealand but by no means universal.

Regarding ferrocement, you and Graham are both right in pointing out that cheapness can no longer be a valid reason for choosing ferrocement (it never really was) and as the method has now lost its popularity the following remarks may be of little interest:

• ·        The “one shot” plastering method you describe is standard fare, but in fact in New Zealand, this method went out of favour very early, to be replaced by what Hartley publicised as the Sayers 2-shot method (Sayers was a Whangarei plasterer who designed and built an impressive number of ferrocement boats, many of which are still around.) Nearly all ferrocement boats in New Zealand were professionally plastered on the outside, to a depth of about 2/3 through the hull, the DIY owner usually doing the inside (the second shot) in stages at his/her leisure. The results were considered to be better and the risk of voids reduced. There is more to be said about how this should be done, but probably of no interest these days.
• ·        I think you are right that ferrocement should be coated with an impervious coating (epoxy usually) though I am not certain. I would not dare to try without. However it would be very interesting to see if a basalt fibre reinforced hull could be built without this expensive coating. I have doubts about your suggestion of adding glass cloth to the epoxy, I have seen an epoxy sheath delaminate and fall off a ferrocement hull, and anyway it serves no purpose as far as I can see.
• ·        You are absolutely correct in pointing out the need for an epoxy coating under the engine and in the bilge sump (though I would not use epoxy anywhere else on the inside). Oil is bad for ferrocement and spilled diesel fuel is death.

Since you have raised the subject of ferrocement, I wonder if many junkies realise that by far the greatest number of ferrocement boats built were built in China, around the tumultuous periods around the time of the  "Cultural Revolution" a period in recent history which I find is not spoken of much these days by Chinese people, and about which we in the West know very little. In my travels in China I was never able to see much evidence of the boats, I presume it was a passing phase and possibly the material proved to be a disappointment (like other “innovations” at that time). Still, ferrocement boats and sampans were being built on an industrial scale and it is possible there may even have been junk rigged ferrocement boats in China at that time. I wish I could find out more about that and would love to hear from anyone who knows more. (They were being built in Cuba too - I have met some Cubans in the 1970s who were involved in State-run ferrocement boatbuilding yards.)

Stay safe.

Hi Graham, thanks for your reply post.

Basalt fibre is a lot lighter than steel, but to make a fibre/cement boat lighter than ferro would require a way of rendering the mortar which resulted in a thinner shell, as most of the weight is in the cement. The obvious way is to do a gunnite layup inside a female mould and lay the fibres into the cement, rather than plastering over a mesh matrix. Fibersteel in the US built at least one ferrocement boat in this way. This would not suit amateur one-off construction. I’m like you, too little time left now for too much more of this sort of fooling around. Also, you are right – ferrocement is no longer a cheap way of building (if it ever really was, since, as you say, most of the cost is not in the hull anyway.)

Chop strand mat and epoxy is probably a more rational way to go, but again, not ideal for the one-off amateur. I agree fully with your last paragraph. Something like Annie’s boat would be the most rational choice these days I think.

If you google “basalt epoxy resin boat” you will get plenty of hits. Here’s a promotional video (in a good strine accent) https://www.youtube.com/watch?v=FE7c20jjxrE and here’s a high tech ocean racer in basalt fibre/resin https://newatlas.com/volcanic-composite-fipofix-sailboat/36242/

Stay safe, Graham

PS I like your avatar. Is this your new sail?

I am throwing this out as a distraction from the current crisis.

I recently came across information about basalt fibre as a possible replacement for steel as a reinforcing matrix in concrete – and as a possible replacement for glass in GRP, and carbon in carbon fibre.

Evidently basalt fibres have already been used in boat building – as a replacement for fibreglass in GRP. It is said to have the strength of carbon fibre, but costs about the same as glass fibre. It won’t wick water, so no osmosis either. Anyone had practical experience of basalt-fibre reinforced plastic?

With portland cement, it is being used in road-making and as a reinforcing material in building construction. This is of particular interest for buildings such as wharfs and anything to do with the marine environment as it is non rusting.

It can be obtained in the form of reinforcing rod, mesh, chop strand mat and random fibre.

It is non-conducting so galvanic corrosion or electrolysis are also not an issue. Being three times the strength of steel, it should be possible to use it as a matrix for thin shell structures such as the hull of a ferrocement boat (without the ferro.) I am currently building a ferrocement-sheathed scow and cursing that I have already meshed up with steel and missed an opportunity to try this material, which I think would have allowed a thinner sheath than the 8mm I am aiming for with 18 gauge steel mesh.

I ordered a supply of this material in order to make some test panels as a little project during the coronavirus crisis, but NZ went into a form of lockdown soon after and the materials are now held up in transit. However, I had some samples in the workshop, and a bag of refractory cement. Havoc’s woodstove has a burnt out top, broken oven damper frame and broken grate. This is a challenge because parts are no longer available, iron foundries are scarce in NZ these days and the skill of a free-pattern moulder is now a thing of the past. Marcus wants the stove this winter for heating (and making bread, he says).

Basalt fibres can withstand temperatures up to 1500 degrees centigrade. Could parts be made in basalt-fibre reinforced refractory mortar, using similar techniques to ferrocement? 

I have now made the parts this way and I think the material is not difficult to use. The mesh can be cut with scissors and is a lot more pleasant to use than steel mesh. The chop strand mat looks not as “itchy” as glass, but I haven’t done a lot with glass so not sure if it is easier to use there.  With cement it should have a myriad of applications in the marine environment, provided people are aware of the strengths and weaknesses of reinforced portland cement.  A photo-documentary of what I have done so far may be found on my website at       https://kenyonz.com/page-17    You can ignore the family history stuff, and the general mess. The above link will take you to the unfinished Havoc page and if you scroll right to the bottom you can click on “Repairing Havoc’s Woodstove”.

What I hope for is some feed-back in the way of further information or comments from anyone who has had hands-on experience using basalt fibre.

(PS If you want to fill in time and be distracted further, you might like to look at https://kenyonz.com/page-20. I hurriedly added a button there for a little photo documentary of recent progress in a junk rigged scow project.)