Stan, I've also used the West System epoxy and agree that the viscosity of the unthinned product would be too thick to penetrate very deep into dense end grain. It would also build up on the surface which could interfere with fit of sidelocks and other furniture. But as Bill Schodlatz has pointed out, epoxy can be thinned with solvents. The viscosity of epoxy can also be reduced by heat. Warming the wood is best because warming the epoxy will reduce pot life and cure time, but you can warm the epoxy just prior to brushing it into the wood. There are always trade-offs when you thin epoxy or any glue with a solvent, and this includes cyanoacrylates. For epoxy, acetone or lacquer thinner is better than denatured alcohol because it is more volatile and less likely to get trapped within the cured product.
One of the trade-offs of thinning is a reduction in strength and an increase in porosity. There are no magic bullets and no product is going to make punky or rotted wood as strong as it was originally. Even thicker layers of epoxy as is sometimes used in glass bedding is flexible. And the rotted motor mount stringers in your sons boat would not be as strong as original wood unless you added layers of fiberglass cloth to reinforce the repair. And this all takes us back to the recent thread on solvent soaks to remove old accumulations of oil. We are fooling ourselves if we think we can soak walnut in harsh organic solvents without affecting the strength of our gunstocks. We may be able to stabilize the depleted wood with cyanoacrylate glue or epoxy. But it will never be as good as new sound wood.
