Over the last few days I've been fiberglassing the hull exterior. The layup is one layer of 6 oz E-glass on the hull, reinforced with a second layer below the waterline and 2 more layers along the bow and stern stems. The area where the stern piece joins the hull also gets a reinforcing strip. The epoxy is MAS with slow hardener -- "non-blushing" and one can recoat in 24-36 hours without sanding. It cures slowly so I have plenty of time to scrape the epoxy out of the glass and smooth it out with a roller. It provides a totally transparent layup.
Now that Christmas is over I can get back into kayak building!
Today I sanded the hull down in preparation for the epoxy "seal coat". I used 80 grit sandpaper mounted on a fairing board, which is made from 1/4 in plywood and a couple of wood handles glued and screwed on. The fairing board is supposed to be flexible enough to bend around the turn of the bilge, but either it wasn't flexible enough or I just didn't know how to use it properly and it ground down the hull surface pretty quickly. One is supposed to sand along the grain with the board. Later on I switched back to a foam block with 80 grit sandpaper, then 120 grit to get rid of the deep scratches. The hull felt a lot smoother after that.
Applying the seal coat commits me to a few days of work without a long break, because each subsequent layer of epoxy needs to be applied while the previous layer is still "green" (within 24-36 hours) for the epoxy layers to bond to each other.
In preparation for the seal coat I cleaned up and vacuumed the shop and turned the heat on with the kerosene heater and an electric heater to get the shop temperature as high as possible. Then I waited and watched the Newfound Woodworks DVD on fiberglass and epoxy application yet one more time. The wood temperature needs to be falling when the epoxy is applied. Since wood is so porous, if the shop temperature is rising when the epoxy is applied any air trapped in the wood will "out gas" and form bubbles in the epoxy. A hot shop and warm resin reduces the viscosity of the epoxy and makes it easier to apply. The designer of the kayak Rob Macks recommends a shop temperature starting at 85-90 degrees but there is no way I'll be able to achieve that this time of year. After a hour or so I only got it to about 70 degrees and then I turned the heat off so the temperature would fall.
I applied the epoxy using a spreader, brush, and roller. I sawed a 9 in roller in half to get two 4.5 in rollers and unfortunately little fibers from the rough edge came off got trapped in the epoxy, so I ended up spending a lot of time brushing out all the little fibers. On the Newfound Woodworks DVD they recommend brushes "made in the USA" because the imported ones tend to defoliate when exposed to epoxy. Interestingly, the ones they sent me in the kit say "made in Indonesia"! (I'll have to ask them about that). The kit uses MAS epoxy with slow hardener, so it cures slowly and there is plenty of time to spread it and brush it without having it kick off and trap a lot of bubbles. The end result is a very thin layer of epoxy which brings out the color of the wood and which will help prevent bubbles from "outgassing" and "starvation" of the fiberglass when the fiberglass is applied and "wet out" with the next layer of epoxy.