Over the years, I've tried dope and talc (or corn flour) as a filler. Invariably, months after the model is flying, the grain is as obvious as ever. GMA once commented that you need to use low shrink or no shrink dope, which fits with my experience. Here in Oz, the only dopes available are really aggressive - one brand I bought could warp sheet steel. We don't have all your fancy dope products (radio fliers don't need them) such as reducers, etc, all we have is common or garden variety dope.
Can I add something to high shrink dope to make is suitable for filling? I've heard of adding castor oil but can't remember why. And how much should I add (we get the stuff in 1 litre cans).
Cheers
Richard