I don't know if it's just me but I am finding it very hard to get builders to progress to Master level. I have one, but the second one I am working on seems to be stuck on the adept level. I had him help on building the dam and the sewing hut, plus he build an ordinary hut all by himself. Since then I've had him almost constantly working on fixing the huts and yet he never seems to progress. Unfortunately I made the mistake of not having him work on cutting back the thorn bush, because I assumed he would advance to Master level without that. Is there anyway I can speed up his progress except forcing my population to grow so they will need a third hut?