> My understanding is a wire frame is coated with stiffer concrete.
> For example a chicken wire canoe is plastered with stucco. Concrete
> is not that strong by itself, it usually needs some sort of reinforcement.
> A male mold could be covered with a loosely woven fabric and coated
> with a runnier mix.

As Nick says, the idea is to make a wire structure and cover it with concrete. Stucco is a compound like concrete, and not particulary suitable for this process. You want a high strength concrete. Since the wire structure is self supporting very early in the process, you don't need male molds, or any kind of molds. If you want, the shape can be made free form, or you can use the frames from a conventional kayak, canoe, rowboat, or sailboat design. I read one book on concrete boats where the author made a form for a rowboat at the beach simply by heaping damp sand in the desired shape.(Kinda like building a sandcastle) Over that he set several layers of wire fence material ( like the kind used for restraining chickens).

Those layers of wire were tied together every few inches with short lengths of wire ( sounds like how stitch and glue boats are held together). By this time the entire boat is a thin metal structure with lots of holes between the wires. from the fencing material.

A THICK, not thin, mix of concrete is applied to the wire form with a squeegee, or similar tool, which forces the mix into the wire fabric. Excess concrete which comes through to the inside is squeegeed off. When you are finished, the hull thick ness is about the same as the thickness of the several layers of wire or fencing material you started with. If you can still see some of the wires showing through then you have it on thin enough. A typical hull for a canoe or kayak might be 1/4 to 3/4 inch thick. They call this stuff ferroconcrete because of the amount of iron in it from the wire reinforcing. If you work with a conventional high-strength sand mix you'll probably get a 17 foot canoe that weighs in the 100 to 200 pound category. While this is high for a canoe, a boat that size has a typical carrying capacity of 900 to 1000 pounds, so there is plenty of capacity for cargo and paddlers. With a shorter boat the hull is not much lighter, but the speed is less, and so is the carrying capacity. With a kayak, if you make a deck out of the same type of concrete the weight of the boat will increase.. Since typical kayaks are narrower than canoes, and have less carrying capacity, you may find some problems in designing one. Colleges that compete in racing concrete canoes insit that they have enough flotation built in so that the boats float even if the capsize and fill with water.

With unconventional concrete mixes -- and these could be anything someone wants to call concrete -- you can vary the strength and the weight a lot. I have read of and heard of mixes of chopped styrene foam, or expanded styrene pellets mixed with portland cement as a possible lightweight concrete for these kinds of projects.

A 19 pound kayak sounds like some engineering student's final term project. At that weight I have no idea how strong it would be. If this story is on the net I would appreciate it if you would give a URL for it. There are many internet references to concrete canoe races. Use any search engine. You'll find many links there that will give more information on this topic.

With the exception of canoes with large amounts of foam, and kayaks with sealed air chambers fore and aft (preferably filled with foam, too) I personally think a lot of the designs I've seen for these things are very dangerous. The method of construction is really best (in my opinion) for larger boats: Sailboats, barges, oceangoing cargo boats, etc. where the relative ease of construction and material costs make them competitive with steel hulled boats. They are reasonably fast to construct, and reasonably inexpensive.

Theoretically you could lash together an ocean liner using many layers of 1/2 inch rebar, baling wire, and a pair of pliers. You could then coat it with concrete, using a scrap of 2 x 6 for a squeegee, making this an ideal process for building navies in out-of-the-way places.

Next time you have your forms set up on your strongback for constructing a stripper, staple several layers of chicken wire over the forms first, and knock out one of these things. ( you pull out the staples when you tie all the layers of wire together)

While we are at it, you could also cover the wires with fiberglass fabric and resin on both sides for another unconventional method of construction. While it is a simple process, which kids can easily do, and I have suggested it as a camp activity for Boy Scouts, the reality is that there are great fears regarding liability and safety if these boats are used by kids.

Hope this helps inform you Paul Jacobson