Since the 1970s, which seems to have been the heyday of ferrocement yachts for the leisure boat industry, concrete technology has made some significant advances. Specifically, glass fibers and superplasticizers have improved the workability and strength of concrete.
Glass fibers provide more anchor points for the cement, much as rebar does but on a more localized scale. Superplasticizers have been described as the equivalent of a dryer sheet for cement. It breaks the electrostatic bond of cement molecules which lets the concrete spread much more evenly and consistently.
This makes me wonder if it's time to look at the ferrocement yacht again, at least for the DIY boat builder?
First, what is a ferrocement boat? Short version, ferrocement boats are wood (or whatever, I guess) framed boats covered in wire mesh on which a cement mixture is placed. Done right, weight was about the same as a steel boat.
Superplasticizers application could improve ferrocement boat building in three ways: 1, the cement mix spreads much more evenly, leaving less voids for the sea to get in; 2, it increases the compressive strength significantly; 3, it can remove the need for a "steam hut" used to cure the mixture on the boat hull. (Concrete cures stronger when it's water evaporation is slowed while curing.)
New glass fibre technology, although it doesn't add much normal (compressive) strength, does address two of concrete's "weaknesses:" 1, it's normally weak(er) in tension than other materials, and more importantly to our discussion; 2, it's brittle. The glass fibres of today address that and a lower brittleness of a hull could be of high interest to someone with the misfortune to run aground.
How to Build a Boat Out of Ferrocement - DIY - MOTHER EARTH NEWS