I never used ashes.
I've done it by reaming pipe carbon out, mixing the carbon with honey, then filling the hole with this cement, letting it dry for a day, then smoking it. Sometimes it takes two treatments.
This is interesting, are you also grinding the carbon into a finer powder?
I don't do my own reaming at all and the few times I've seen it done it seems to come out in chunks that I wouldn't guess would be manageable for mud making.