Finishing the Build...

 ... in early preparation for the October 13th bloomery iron smelt at Wareham

The standard furnace build here by DARC uses a mix of rough thirds of powdered clay (EPK), course sand, and dried, hand shredded, horse manure (last year's droppings). This last adds short pieces of softened grass that act to bind and leave spaces for steam to escape to limit cracking.

 

When done, the exterior is wound with rope to help prevent external sagging (seen at the bottom of the image. The furnace body was 20 cm tall at that point.

The interior is filled with a dry mix of half sand, half wood ash (from the wood stove). This acts to both stabilize the structure, but also pull moisture from the wet clay. This image taken roughly 20 hours after the lower portion had been finished. The darker ring in the packing next to the walls shows absorbed moisture.

 

In high 20's C clear Ontario weather, the soft clay had already dried to 'leather hard, when work resumed the next day'. Because I had some concern about the relative moisture between this layer and the next one to be added, I had incorporated a 'Beardsley Break'. A depression is made on the top edge with your thumb, creating a U shaped channel. In this way if the expected crack develops between the two additions of clay, the channel will both lock the new upper section in place, but also serve to limit / prevent any working gas seepage at that band.

Finished clay build. Furnace is actually straight!

The bulge at about 40 cm is because the section of previous furnace had thicker walls than the fresh clay build below. The internal diameters match. This is the first time I have attempted to directly re-use a section of an earlier fired furnace.

Total shaft height at 62 - 65 cm.

 

I am expecting some cracking problems with the mating of fresh (shrinking) and old (stable) clay sections. Once the furnace has air dried and then gently heated, it will be bound with fencing wire to brace any cracks Iike the loop seen on the re-used section. (The rope is removed when leather hard)

I intend to mount four pieces of angle iron into the inner corners of the block plinth to ensure stability. All in aid of being able to re-use this furnace several times, hopefully.