While waiting for the chamber steel to arrive I set to work on the firebox. Basically relaying the grate and insulation – in theory. In practice however, once I examined the state of the arch and supporting walls I realised that they needed more maintenance that anticipated. The walls on one side had moved and needed straightening and then additional exterior brick work to brace them and the arch wedges on one side needed replacing, which is a tricky and rather brutal job because the integrity of the arch is at risk.
Once that was completed I laid bricks in the throat zone and then started laying the grate. This grate is designed for burning pine, so the gaps are quite tight, keeping more of the embers on top of the grate rather than having them fall through to the ember beds. Harder woods would require a wider spacing. The central grate is also gapped differently to allow more ember air to rise up close to the stoking port and not deeper into the firebox.
Then the firebox front is closed in and bridged over the main stoking port. The first layer of the adobe is cement stabilised and has vermiculite, crushed old adobe and pumice sand as a way of sealing the cracks and coping with the heat. Then a layer of adobe that is bonded with clay and again has a lot of vermiculite, pumice sand, crushed old adobe, paper and sawdust. There is one more layer to go, which will be a big batch of clay, hay, vermiculite and sand that will cover the chimney, chamber and firebox.