Hi Dan! - The fire bricks used in kilns is very porous material. That is not what causes the uneven temp in this kiln, though. The three burners are located at the bottom of the kiln, and stacking the shelves so the flames make their way back and forth between them is a challenge. If I just stack them evenly, the flames essentially go up the outside of the shelves and the bottom gets very hot, and the top doesn’t get hot enough. The trick is to try to keep the flames from escaping the top too quickly, so heat builds up there as well. The challenge, though, is to not restrict the flames at the exhaust vent, or I’ll cause a reduction, which changes the outcome of the glazes. It’s always a challenge!