Choosing Glass and Epoxy
Epoxy choice should not be a random decision nor one based primarily on price if you are looking to build the best boat possible. Think of your resin, glass, and shop environment as a system. The three must complement each other to work effectively. Thick or tightly woven cloth requires runny, slow hardening resins for good results. Open weave cloths are much easier to wet out, but harder to fill. Resin cure times can range from minutes at 90 degrees to days at 50 degrees, so the right resin for your shop temperatures can make a big difference.
Not all epoxy types are equal in heat tolerance and strength, and some popular manufacturers do not provide this info for their products. Have you noticed that most of the best builders use well known and proven brands of epoxy? Since I put a lot of work into my boats, I don't want to experiment with something that took so long to build. I stick with the best products I can find, not the cheapest. Currently I am using System Three Clear Coat and MAS. Both of these work well for me and have good strength and heat tolerance characteristics.
The second major choice is which glass fabric to use. I used the typical plain weave 6 oz. e-glass of my first two boats and that went fine. Then I heard that using multiple layers of thin satin weave cloth will give a better glass to resin ratio resulting in a stronger boat or at least one of the same strength but at less weight. I built a Redfish Silver this way and it came out reasonably light. However this boat gets dings, scratches, and dents easier then my okoume plywood boats. The problem is the soft cedar. Strip built cedar kayaks need a heavier glass laminate to be as tough as okoume plywood. And then the two types will likely end up weighing about the same as well.
The most recent boat, a Redfish King, was built using 6 oz. satin s-glass. Even though it was difficult to work with, this glass has produced a much tougher boat without any weight gain. While the difficulty in wetting out this cloth was expected, I was surprised by other problems. Due to its superior shear strength over e-glass, it sometimes delaminates from the wood core at the edge of saw cuts or drilled holes. It's just so tough it pulls away from the substrate instead of cutting cleanly. I never have this problem cutting e-glass. As a result, one must take more care and use very sharp tools. A little touch up with thin resin fixes any problems. In the long run this boat will accumulate fewer glass whitening dings and end up looking better for it.
Like many things, you must choose how much glass to put on your boat in accordance with how you are going to use it and the conditions in which you paddle. If the best appearance is your goal, you might investigate using 3.75 oz. open weave e-glass cloth. It seems to give the best clarity. I have not used this fabric however. For abrasion resistance and strength, s-glass is clearly superior to most fabrics but not quite as attractive. All that being said, regular 6 oz. e-glass will build a fine boat for most purposes.