The result isn't too bad (sorry it's a bit hard to see in this photo - I really need to work on my photography skills!). I had a couple of hiccups to start with. Firstly making the grey wash too thick and dark and despite immediately watering it down as I hadn't sanded the walls first (another one to remember!) the paint sunk into the ridges and wouldn't dilute!
I then ended up going totally in the opposition direction as I found that if you wet plaster (like with a colour wash) the plaster looks grey and discoloured. When you come back to it after it has dried it looks exactly the same as when you started! I'm not sure if I was doing something wrong but I ended up just kind of slapping it on and hoping for the best when it dried.
I still need to do a bit more 'sooting' up above the fireplace but I think that is more or less it for the walls - if I can ever get the bits of masking tape off that I have managed to plaster to some of the beams (pulling making tape off while the plaster is wet is highly recommended!!!).
Next step - a flagstone floor made from more polyfiller. I'll keep you posted.....