: But lets get back to what matters. You mentioned that the cedar is strong
: enough by itself for a kayak. I agree. The problems are impacts and
: abraision. I think that it would be very interesting to compare the damage
: created by different lay-ups under impact. Minimizing delamination between
: the wood and glass is the key.

I agree that if you get everything else "perfect" most failures will be somehow related to delamination. While a few of the test samples showed sharp, distinct breaks in the fabric and wood, most showed some signs of delamination that probably happened before final "failure".

With this in mind we need to think about how to maximize the inter-lamination strength. Seems you want a strong bond to the wood, and tight spacing between the cloth and wood.

A strong bond requires good absorbtion of the resin into the wood to maximize the adhearing surface area and mechanical grip and the resin having good adheasive properties. Epoxy is a good adheasive and this is one reason why it is prefered over polyester resin. Not using too fine a sandpaper will promote good absorbtion and make a rougher surface for a better mechanical bond, but it may also lift the cloth away from the wood more than if the wood was smoother. Also feeding the wood resin until it stops absorbing will maximize the absorbtion. But, greater absorbtion will increase weight.

I generally recommend a seal coat on the wood before glassing, the downside of this is it limits how much resin is absorbed (good for weight, bad for strength), it makes it so some of the epoxy-to-epoxy bonding is mechanical not chemical, and it will tend to build up a layer of epoxy that lifts the cloth off the wood. The problem with skipping the seal coat is it is ha26tm to control, as the wood keeps absorbing resin so the cloth may end up starved which will produce air bubbles and visible cloth.

I would also speculate that Mike's idea of using hardwood may result in a weaker epoxy-to-wood bond because the hardwood will not absorb the resin as readily. But then again, the may just mean that you don't need to worry about doing a seal coat at all.

I'm sure that if someone really wanted to get involved with the material science of wood-glass-epoxy composites that there would be a lot of factors that would have to be considered to make the "ideal/optimum" layup. What I am not so sure about is if the "optimum" layup would be a large improvement over a well done "standard" layup. I'm sure the standard can be improved upon, but when you take into account factors like ease of building, time, cost etc, the standard (6 oz glass on 1/4" cedar) works pretty well.