Our canoe’s concrete mix is designed to be less dense than water, in order to ensure that it will float (although other factors also influence whether our canoe floats). This year’s mix is less dense than water, but only just. So as an added precaution, we add foam and air pockets (encased in concrete) to the canoe in the bulkheads (at the bow and stern). This way we have some added flotation factor just in case something goes wrong with our mix design!
Asides
Endless hours of canoe-pour prep…
It actually takes more time to get the canoe ready for pour day than it does to pour it. Excluding the mix design (which obviously takes a lot of effort), preparing the mold is our biggest pre-pour task this year. Once we cut the rough shape from styrofoam blocks, we need to sand them into the more accurate shape, then glue most of the mold pieces together, tape the rest together, and do some final sanding.