I am attempting to make some Terra Preta by adding ground charcoal to compost for the garden. I've been putting some chunks into a can and grinding it with a worchestershire sauce bottle. It's not stupendously effective. Beating on it with a sledge on concrete is sloppy and wasteful.

So, does anyone have any clever, easy, simple, non-messy (mostly) ideas on how to grind up about a cup of charcoal at a time? I have a mortar but no pestle, and haven't been able to find a suitable rock.

Thank you for any ideas.

Sue