: Has anyone tried different adhesives for the tape in stich and glue? I am
: curious how polyester resin would work. I know the strength would be less,
: but would it be enough?

: Thanks- Kristopher

The people who originated stitch and glue techniques did so with polyester resins. Epoxy is a relative late comer to the scene. Is polyester strong enough? Yes. Absolutely.

There is an older method of building boats with plywood panels which uses chines, or long pieces of wood, at each panel joint. You would make a frame ( or a series of frames) to hold the chines in place at all the "corners" or seam lines. At this point the thing would look like the frame for a skin on frame kayak, and if the chines were strong enough, you could probably cover the thing with canvas and paddle it. Instead of flexible canvas, though, people used solid panels of wood or plywood.

The layout of the chines gave you guidelines for cutting the panels to size. Then the panels of plywood would be applied and glued and screwed to the chines. Since the panels came together at varying angles along the length of the boat, the big trick with this method of construction was to make the edge bevel of those chines meet the panels. A lot of the old plans I've seen call for using strips of cloth (cotton, not glass) soaked in glue to ensure a good, tight, waterproof seal along the length of these seams.

Stitch and glue techniques basically throw away the frame and chines from this old process. As long as the panel are accurately cut -- and we can do that by using either full size patterns, accurate offsets, or computer-assisted manufacturing techniques -- the parts should go together properly without the frame. The seam sealing, and minimal strength that the chines provided is now supplied by a thick composite of resin and glass fiber that size for size is far stronger than wood. This material is applied dierectly to the seam, so it fits perfectly, too. In effect, the panels serve as a mold for casting a glass-reinforced plastic chine directly in place. Once the resin hardens, that "chine" is in there to stay. Covering the outside of the seam with a layer of glass cloth or tape provides another reinforced barrier against water leaking in through the seams. Consider the actual shape of just the glass tape that covers the outside of the seam. It folds over the seam and forms an "L" shape, which is a pretty strong shape, whether you are looking at fiberglass, or angle iron.

It is a toss up as to which resin to use. There is no clear winner, but the trend it toward epoxy and away from polyester. Polyester does not work well with red cedar (the wood is too oily) so it is generally not used for cedar strip canoes or kayaks, unless the wood is sealed before the glass and resin are applied -- but it works fine with white cedar and pine. Gil Gilpatrick's first book on strip canoe building, and David Hazens book, both dealt with uisng polyester. The newer editions of Gilpatrick's book have changed to recommending epoxy. Polyester resin has the advantage over most epoxies in that it is more resistant to UV light, and you can buy it for as little as $13 a gallon. As a result, it might last longer than epoxy. A lot depends on the care that is taken with the boat. Epoxy needs to be protected from UV, usually by a coat of varnish, and usually you have to redo this every year or two. Polyester doesn't soak into the wood to protect the wood from moisture -- epoxy does. If you have a big boat that is kept in the water all year, then after sometime you mght have problems. This is less common with canoes and kayaks, though, as these small boats are usually stored out of the water. If you are building a prototype, lauan plywood and polyester resin is a great combination as the price is so low, the resin sets up fast enough that you can put on 2 coats (or more) in a day, and since the polyester resin won't comepletely cure in the presence of air, you don't have to sand between coats. The first coat stays tacky for some time, and finally cures after the second coat is applied. (The last coat has wax or styrene plastic dissolved in it, which rises to the surface to provide an air barrier so the resin will cure)

Hope this helps.

Paul G. Jacobson