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The kiln has been really inconsistent the last two firings, so I spent a little time on prep and maintenance, before I started glazing.
Mostly this involved hitting it with a hammer.
Brick expands with the kind of heat we subject it to, and contracts again as it cools. Potters are cheap, always planning to reuse materials when the day comes that we have to tear down and start over, so all our kilns are dry-laid. No mortar.
So the bricks can move independently, but, because friction, not necessarily mean they move back to their original location as they cool. With enough repeated expansion/contraction cycles, you can develop fairly large gaps between bricks, particularly where they're not contained, like in the chimney.
Where they are contained by steel, in the walls, they can start bulging out.
So I took a hammer and two-by-four and banged my way around the chimney, making the gaps go away. I also pushed the bulges back in on the back and rear side walls. I bopped on the door sills, pushed the door bricks tight (this also makes it much easier to open and close the kiln). I poked my phone into the chimney and took a picture, to be sure the flue was clear. (This took a frustrating ten minutes before I realized, via flash photo, that the damper was still closed. Once I opened it up, all was okay.) I even unscrewed the burner venturis and banged them on the floor, to know out any loose scale and brick crumbs.
I must have done something right. For the first time since January, it fired evenly top and bottom, though it still stalled a little at the very end. Cone 9 was down at 5 pm, but cone 10 didn't drop until after 7. Still, even firing, reasonable amount of gas--66 units. I'll find out tomorrow how the actual pots look.
Mostly this involved hitting it with a hammer.
Brick expands with the kind of heat we subject it to, and contracts again as it cools. Potters are cheap, always planning to reuse materials when the day comes that we have to tear down and start over, so all our kilns are dry-laid. No mortar.
So the bricks can move independently, but, because friction, not necessarily mean they move back to their original location as they cool. With enough repeated expansion/contraction cycles, you can develop fairly large gaps between bricks, particularly where they're not contained, like in the chimney.
Where they are contained by steel, in the walls, they can start bulging out.
So I took a hammer and two-by-four and banged my way around the chimney, making the gaps go away. I also pushed the bulges back in on the back and rear side walls. I bopped on the door sills, pushed the door bricks tight (this also makes it much easier to open and close the kiln). I poked my phone into the chimney and took a picture, to be sure the flue was clear. (This took a frustrating ten minutes before I realized, via flash photo, that the damper was still closed. Once I opened it up, all was okay.) I even unscrewed the burner venturis and banged them on the floor, to know out any loose scale and brick crumbs.
I must have done something right. For the first time since January, it fired evenly top and bottom, though it still stalled a little at the very end. Cone 9 was down at 5 pm, but cone 10 didn't drop until after 7. Still, even firing, reasonable amount of gas--66 units. I'll find out tomorrow how the actual pots look.