So, yesterday I got some real charcoal. Or as they call it "Natural Lump Charcoal". "Cowboy brand". It gets much hotter :)
I redid the brick layout to make it more of a "front and back" layout. As it was, I could only stick the tips in from the top, and couldn't heat any part more then 4 inches from the end. So, I kept the base but for the top layer I put two bricks on the side, and put one at the other end laying down, just to help keep the coals from falling out. Finally I put the extra brick on the top(and I really have *no* idea if that helped at all).
I got the fire going, but couldn't get it nearly up to heat. The problem was I still had a lot of ash from the last try clogging the air holes, with that removed it got very, very hot. I couldn't get the iron whitehot, but with only a little rearrangement that could be possible. I noticed that the concrete bricks were glowing at places, so I stopped working on it.
I put water on it to put it out; in fact, I left the hose running on it for a half an hour, and the bricks were still warm.
Here are the pics: http://flickr.com/photos/30415033@N00/sets/
go ahead and invest in some firebrick - will be a lot more heat-resistant than concrete block and will insulate better.
Also, you -do- want to insulate the firebox - I'd be willing to bet that's whats cutting back on a lot of your heat - forges can be run with wood under the right conditions
btw - have you decided if you're coming up for stones? you better, or danny's going to beat you with a badly tuned piano :)