Fiberglassing

The next step after installing the plywood hull planking is to cover it in a layer of fiberglass for waterproofing and protection.

Fortunately I have experience with fiberglassing from some cedar strip canoes and paddle boards I built so I was pretty comfortable doing it.  I ordered 6 oz fiberglass cloth (i.e. it weighs 6 oz per square yard) and UV inhibited slow cure epoxy from Raka. I’ve used Raka for all my boats and been very happy with it, so never felt the need to try the more well known (and expensive) brands.  

I covered each of the four plywood panels in a piece of fiberglass cloth so the cloth overlapped where the plywood panels meet to form a double layer for extra strength.

I mixed the fiberglass 2:1 in a plastic cup, poured it out on the cloth, and spread it with a squeegee. The cloth turns transparent when wet so the trick is to make sure there is enough resin to saturate the cloth but not float it or leave dry spots. 

The slow cure epoxy gave me about 20 minutes of working time before it started to thicken up, so I had to mix a few batches for each panel.  I had to wait a day for the epoxy to cure so I could feather the edges with a sander so the seams (hopefully) won’t be visible, which meant I could only install one piece a day. 

Two or three more coats of epoxy are required to fill the weave of the cloth and create a smooth surface.

When the filler coats cure, I will sand them to remove any drips and judiciously add epoxy as needed to fill any low spots. The low spots are very obvious because the sanded epoxy turns milky white while the low spots stay glossy.

The above photo is the hull before sanding. Even though sanding makes the epoxy cloudy, it turns clear again when it is wet (or varnished). I’m going to paint the hull white so it doesn’t matter here, but I got Sapele plywood for the deck which I’m planning to keep natural wood grain to match the frames.  It’s really cool to watch the white cloth and sanded epoxy turn transparent when it is wet.

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