Building a concrete canoe is a long and complex process. I’ve broken it down into six overly-simplified steps and illustrated it with impressively bad drawings.
- Design a buoyant concrete: Concrete is made of water, cement, and sand/gravel. To get your concrete to be less dense than water, you must remove the heavy sand/gravel and replace those with lightweight glass spheres. This final mix design is generally found using trial and error, so it can take a lot of time (and a lot of frustration) to design a buoyant concrete mix.
- Design the hull: The hull shape is very important to the overall performance of the canoe. The canoe’s length will affect the top speed, and the shape can affect whether or not the canoe takes on water when fully loaded.
- Build a mold: There are indefinite ways to build a mold. It depends on the materials you have available and the final construction technique you plan to use. The mold can be male or female and should be designed so that removal is simple.
- Build the canoe: Similar to the mold construction, the canoe can be built in numerous ways. If this is your first time, make it as simple as possible. Quality control is difficult to manage with such a large object, so a practice pour could be helpful.
- Properly cure the concrete: Concrete need to hydrate to gain all of its strength, which means that it’s important to water the canoe appropriately. The first seven days are the most critical because that’s when the concrete gains most of its strength.
- Remove the mold: This sounds like an easy step but can cause a lot of problems if you didn’t put a lot of thought into item (3). Sometimes it means you have to completely destroy your mold to ensure the canoe doesn’t break into pieces upon removal.
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