They're a bit tatty on the edges, but I can live with that. I'll be cutting them to make a nice circle anyhow, so I'll just stick the best ones in the middle and put the grotty ones round the edges. I have no idea what type of firebrick they are - yellow, with some red in them, heavy, and bigger than regular commons. And a big letter D stamped on them - wonder what that means?
I felt I should do some real work too, so I mixed three barrows of concrete, bent up some rebar into right angles, and filled the cores of my support blocks, using a couple of bars in each.It all looks pretty ugly inside at the moment. The rebar will tie the cores to the hearth slab, which will be the next thing to be poured. First I need to figure out the best way to hold the concrete in over those very uneven stones.