Real progress

There was a lot of progress made on the kiln today. I've been preparing many pieces and parts, and it was gratifying to see them go up smoothly.

First the angle iron went up. Howard drilled holes into the concrete through flaps on the bottom of each vertical post. The posts are then bolted onto the ground. Stainless steel tie rods were added at the top of each angle iron to stabilize the tops as well as the bottoms. We added valve springs onto the tie rods on top to absorb the expansion of the arch when the kiln is at its hottest.

As we erected the vertical irons, sheet metal with kaowool insulation adhered to it, was slipped into postion. The kaowool is spun alumina, a space-age insulation product that works best when it is not compressed. I had the sheet metal edges folded in a z-shape, so the sides would fit under the angle iron, and the center pooch out to give space for the insulation.

The first photo is the front of the kiln where you can see the wooden arch support above the sheet metal. A close examination shows 8 rows of bricks on each side of the arch support. There are another 11 rows of bricks to be added in the middle/top of the arch. When all the bricks are on the arch support, it is carefully lowered just a fraction of an inch to make sure nothing falls. There is no mortar on the arch bricks or skewbacks, they are held in position by the shape of the arch. Angle iron & tie rods keep the arch bricks from spreading or falling. When we are confident the arch is holding (of course, it will!) the wooden support will be removed from the kiln.

On the left side of the kiln front you can see the white kaowool insulation through holes in the sheet metal. The upper hole will be cut out to reveal the opening where wood can be stoked, and the lower hole will be for a propane burner. There are similar holes in the sheet metal on the back wall. You can see them on the second (right side) photo. The back of the kiln can be seen on the left and the firebox side is on the right of the photo on the right side above. Holes on the far side of the back wall are peep holes, which when opened will allow me to check the heat rise during a firing. The holes on the bottom of the firebox side walls are called "mouse" holes. When these are opened during a firing, they will allow fresh air (more oxygen) to enter the firebox. This would be to encourage a hotter wood fire, when that is the fuel being used.

After the arch bricks are set, I get to go back to mortaring bricks on the front & back walls. My supply of good hot-face bricks is getting very low. I'm trying to use the better looking (newer, less chips or gouges) bricks in the main kiln, where it will get hottest. The chimney can take any left over, old, cracked, chipped or otherwise compromised bricks, and it will not affect the way the kiln fires. I have a number of old soft bricks that I'm planning on using to insulate the chimney until I run out of them. We'll see how much of the chimney will get insulated this way.

next to last row

Today I mortared hard bricks for the 23rd row, and mocked up the soft bricks.
Lots of measuring - and trying to use the odds & ends of soft bricks remaining.
I'm trying to save the last really good back-up bricks for when they will be needed soon.

I can see my stock of really good hard bricks is going down fast.
There are a couple of stacks of hard bricks still to have the old mortar ground off, approximately 40 more bricks. Then there are about another 40 bricks that have a whole lot of junk ground off, that may or may not get done. Last resort bricks they will be called. Only to be used in desperate measures like for the top of the chimney, if a few more bricks are needed.

The arch will lie on the 24th row. The right & left sides of the kiln will have the bricks laid in soldier courses. This means the hard brick will lie from in to outside of the kiln wall. This will facilitate the angle iron that will hold the bricks in tight - and keep the arch from falling.

I will mortar the 24th row of bricks on the back wall, but not the front wall. I think it will leave it easier to handle the arch support from the front.

Before the arch support is laid, I have to cut skewback bricks to help support the arch.
The photo shows the arrangement of bricks in the arch. There will be 5 rows of bricks laid in the exact same way from front to back of the kiln. Howard & I decided to lay the arch without cutting any bricks. He has made kilns in this manner and assures me they work just fine.

I have finished reading Daniel Rhodes Kilns: Design, Construction, and Operation which was first published in 1968 and updated in 1981. It is amazing to me how much of the info is still current - 99%. He has some great kiln designs in the back, and my kiln is just a variation of a couple of his designs.
I seriously considered a catenary arch kiln, but it would have had 2 fireboxes on opposite sides of the kiln, with 2 stokers needed. I really want a kiln that could be fired by one person, with the option of 2 persons if desired.