Funny you should ask neil 
Last weekend i had 4 failed attempts at just putting the sand in the flasks so never got to switch on the furnace even.
Today i am trying again but with 2 failed this morning again i think i am getting closer and just in the middle of the next one.
The probs i have had have been sand sticking to the former, so not enough wax/talc/release agent which i hope now to have rectified. Not enough CO2 getting through when i tried the silica sand method, that i think actually was due to a poor mix by me.
This one i am waiting for the silica sand to be nice and dry for my final mix and hopefully its a goer, the petrabond one this morning the edges came away with the former so i dont know yet on that one.
Was getting to me a bit but i have keep saying its my first attempt and as long as i keep getting a bit closer i am going the right way
, as you can gather i am spreading the eggs by trying both methods
Bernie