Just curious, I was cleaning out the firebox this morning, and felt considerable resistance with the shovel on the bottom. I was afrait that my firebricks were cracked, and since the stove was cold, I ran my fingers over it and found a rough, hard substance that would not come off easily, did get a small piece that looked like tan gravel. I suspect that the load I purchased from a dealer that was caked with mud baked it either into a glass or a brick-like material and fused it to the firebrick. I am afraid of trying to remove it for fear of damaging the bricks, but it is annoying. Any thoughts?