Posted: 30/10/2012 at 20:03
In the 1970s I was a chimney-sweep, very few about these days as coal fires have gone out of fashion. However, I used to handle lots of soot. A local small nursery used to buy the soot from me at 50p a bag. He claimed soot was the best thing to use for breaking down clay and bought many pounds worth from me. I don't know how available it is to you, but try it if you are able.