Our objective was to do the splice in one session. That requires taping the second side before the first side is dry. And we wanted to do multple splices in one session.
We came up with what is a simple quick method. We laid out two sheets butted together on some benches and wetted out the edges about 2 inches on either side with unthicked epoxy. Next we applied a 6 or 8 ounce cloth cut to 2 inches (approx) wide. We then saturated the cloth, and applied a plastic sheet to cover the joint. Next we rolled out as many wrinkles as possible and screwed on a piece of plywood we started calling "splice scabs".
We had some initial failures because the scabs were too narrow and thin. This allowed the joint to flex when we flipped them over, creating a gap leading to failures. After that we found we need a 12 inch wide splice scab of at least 1/2 inch plywood.
After screwing the scab to the joined plywood we flip the assembly over, and wet out the second side. But before we place the 2 inch glass cloth we add some epoxy thickened with 406 colloidal silica fibers. Then we saturate (again), plastic film, roll out wrinkles, and add a screwed on (second) splice scab as before.
The completed scarfed set becomes the bench for the next pair of sheets. Using other scraps of 1/2 inch plywood to keep the next pair from sagging, you can do multiples of any number.
Fiberglass tape is easier to use, but will not disappear when you roll because of its edges. That is why we cut our own strips from wider cloth. The 406 suspends the epoxy at the joint and prevents a capillary action into the wood that would allow the joint or any space between the sheets to fail. Heavy plastic such as contractors garbage bags roll our flatter and make for easier finishing. And you don't need a press with this technique.
Vince Campbell
September 28, 2007
