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Dave and Anke
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Tuesday, March 12, 2019

Getting Concrete... Sorta

Why concrete and box barges go together?

You say to a brick, 'What do you want, brick?' And brick says to you, 'I like an arch.' And you say to brick, 'Look, I want one, too, but arches are expensive and I can use a concrete lintel.' And then you say: 'What do you think of that, brick?' Brick says: 'I like an arch.'

--Louis Kahn

Getting Concrete... Sorta

In the never-ending search for cheap yet robust materials, concrete keeps popping up.

A boom in ferro-cement boats (concrete hulls built around a steel frame and mesh) left a mixed impression. Poorly made boats crumbled from their first days... water infiltrated the concrete and the steel bits rusted expansively, breaking up more concrete... and repeat. Well made vessels from that time can be told at a glance; they look great, structurally (cosmetics can challenge any vessel!).

But I'm more interested in wood-cement composites... the hull substantially wood, with cement or concrete playing supplementary roles.

Once again, I'm short on personal experience, but here are some evocative stories:
  • One fella wrote that, in the plank-on-frame boats he'd seen with internal concrete for ballast, he noted that the hull never had any rot issues below the concrete level (alkaline environment). Frames would rot right at the surface where bilge water collected and sat. He suggested fairing the concrete up the sides and, over a number of years, had had no more rot problems in that area.
  • Another remarked that in his years working with concrete, wood or tools that had been splashed with cement slurry and not cleaned up were extremely difficult to break free, later. If he did make the effort, the wood was invariably bright and tools invariably shiny under the cement (I can personally attest to this).
  • Samson (a leading ferro-cement design and construction firm) developed a method for planking up a hull as a permanent male mold, to the outside of which ferro mesh was stapled and cement sheathed for a fully composite hull.
  • George Beuhler was an advocate of ferro-concrete keels for us cheapskate builders. He'd up the density with boiler plate punchings, tire leads and spent sand-blasting shot.
  • Greame Kenyon of New Zealand has built and lived aboard small NZ Scows (near-box barges, but with the bottom Veed forward and brought out to a point). He has decades of happy experience sheathing his scows to above the waterline with ferro-cement. His method is a couple of layers of wire mesh affixed to the hull and finished with concrete to from 1/4in to 5/16in (6mm to 9mm-ish). It protects the wood chemically and mechanically, while concentrating its weight low in the hull.
  • Some exciting developments involve fiber reinforced concrete in which a whole array of fibers (in random strands or fabrics) are employed.
  • Phil Bolger suggested an internal ferro-cement slab (faired up the sides as per the first fella) to stiffen the bottom, provide ballast and a well sealed bilge.

Taking all these snippets together, I wonder if one could:

  • Sheath the hull to well above the waterline with ferro- or fiber-cement.
  • Thicken the bottom sheathing at will to provide ballast and grounding protection.
  • 'Paint' as much of the hull as desired with a fibered cement slurry for rot protection, inside and/or out.

Finishing the concrete above the waterline is straightforward sealant plus paint. Below that, I'm guessing a few thick coats of (coal tar?) epoxy (resin) with a compatible antifouling paint over would work as well as any more standard approach.

Me? I'm scratching my head over how to attach copper plate over a fiber- or cupro-cement layer!


  1. Copper plating over cement only with some miracle stickem and no drilled holes would seem prudent. Any kind of abrasive or point loaded grounding would seem the mortal enemy of concrete. Immense utility in casting it as a ballast slab it would seem. If hull sheathing it makes sense to minimize flexing to the max thus internal stringers and frames?

    Concrete, recycled steel plate, local wood strip planking.... all make sense as solutions to increasingly expensive and hard to source GOOD plywood. And pricey epoxy. Totally in tune with the overall thrifty nature of a barge boat build. Exciting in a flat bottomed boat geek kinda way.... oh yeah.

    1. Hi Robert,

      I've thought a lot about it, especially in connection with Dmitry Orlov's QUIDNON project.

      A bit of drilling seems okay, so long as we steer clear of reinforcing metals within. I see it done all the time in bridges.

      So my best thought is to drill oversized holes on the pattern of the plate fasteners, and fill them with structurally thickened resin (many are commercially available, or DIY). Either the fasteners can be set through the plate into wet glue, or each can be pilot holed once set up.

      Point loads at each fastener are very low (divide plate weight by number of fasteners in pattern).

      RE Bottom Flex... If building a slab, rod and mesh should, I think, provide a slab which significantly reduces flex, but can ride what remains with ease.

      If only a thin layer is desired, I'm interested in fabric or fiber reinforcement, which allows for a lot of flex.

      Reinforced concrete is amazingly flexible... Here's a youtube of the Tacoma Narrows Bridge. Note how flexible the concrete is, and how well it stands up to extreme flexing. When it does go, it looks like component linkage failure, to me, rather than component failure.

      All in all, impressive stuff!

      Dave Z

    2. Colvin Bookes' book on ferro cement hulls can be found on the website 'world of ferro cemtnt boats' Very interesting info!

  2. I read a very interesting article about a mixture of latex paint, Portland cement and sand on burlap.
    Might be a good way to strengthen the hull while helping to overcome the challenges of dry rot in wood hulls

    1. Hi,

      I'm guessing it would be a good coating, but not sure about adding strength, as it sounds far more flexible than the underlying wood. I'm certainly interested in the preservative aspect of Portland Cement.

      Meanwhile, a concrete pro told us of various latexy additives to concrete which helped with flexibility and repair bonding. He thought they'd be useful in their own right on wood... possibly with a fabric matrix for sheathing. Might be a cheaper alternative to TBIII?

      Burlap used to be common as a deck sheathing, set in a latexy lagging compound (Arabol, then other products). It lasted about 15 years.

      But a friend commented that he preferred a synthetic cloth (e.g., glass, acrylic, polyester, nylon) as, if water DID get into the material, there would be no rot issue. Since then, we've used synthetics with success.

      Do you have a link for the article?

      Dave Z