On the basis that the strength of a resin is dramatically increased with the addition of some fibrous support, for the optimum strength of whippings you would need to make sure that the resin deeply penetrates the whipping thread. I stripped off some rings recently where I had applied normal thickness of epoxy resin to the whipping and noticed that the epoxy had hardly penetrated the thread. So on the last couple of rods I've made I diluted the first coat of a slow curing epoxy resin for the whippings with toluene (care, good ventilation) in about 1:1 ratio of toluene to resin (Sensei). This is a much greater dilution than recommended with, eg IPA or actone. This mixture seems to have deeply penetrated the thread and so should be stronger, though I have no actual data to support this. A down side is that it dramatically changed the colour of my thread from a grass green to a dark brown! I doubt if colour fasts would help as they probably, and I'm guessing here, work by preventing the epoxy from penetrating the thread! Diluting, at least this, epoxy with toluene didn't seem to affect the hardness of the resin, as it set hard and I was able to sand down any imperfections. The rest of the layers I built up as normal.