I have been thinking ahead about ballast. Thinking that ready-mix concrete might be the answer I started a thread about concrete as ballast on CWF and the resulting discussion I think I might have found the perfect ballast material. Seems concrete might not be a good idea. I say might as there seems to be no clear feeling about it accept in France boats built after 1997 are not permitted to use it. DBA article
So then I thought Granite. I rang my brother (he owns a stone workshop) and asked what he did with his scrap, i.e. the bits he cuts out for cookers, sinks and other wastage. He puts it in the skip he told me, about 3 tons a month! 30mm thick is 90kg sq/m its non porous, its lose and for me best of all its free.
These are typical off-cuts and I can use it in 3 layers if need be. Each one of my bays is .8sq/m so I could get over 200kg in each.