Right … so I stripped the form work off of the footing for the rocket mass heater. The footing looks good; the perlite gives the footing a rough look, almost like having rice krispies in it.  We did not do much to smooth the surface of the concrete pour, working the concrete makes it more dense which reduces its insulating ability.

After the form came off the footing we started  moving the fire bricks into the earthship.  As we moved the bricks we scraped off any old mortar and cleaned the bricks so they would stack nicely as we built the core of the heater.

Next we placed a 6″ diameter straight section of single wall chimney pipe in the space we left in the footing for the ash clean out under the feed tube.  This 6″ long piece was then embedded in concrete (same mix as before) to hold it in place.  I drilled two small diameter holes in the end of this pipe that was to be embedded in the concrete and before placing it put screws in the drilled holes.  The ends of the screws stick into the concrete used to embed it in place, and will act to hold the pipe in place.  Finally, I put a cap on the pipe.  (In order to get a 6″ length of chimney pipe I cut down a 1′ length that we bought.)

We then placed the base layer of brick down for the core of the mass heater.  Before placing these bricks we put a 1/2″ layer of concrete (same mix as before) on top of the footing.  The goal here is that the bricks will be set and leveled in this topping layer.  I am not sure how effective this step will be in the long run … worst case this topping will crack, but I do not think it will affect the integrity of the heater.

I then mixed the refractory mortar that I bought in Kamloops with water (fairly runny). I placed the bricks for the next layer of the core … and it was tough. Turns out the mortar I purchased was for repairing cracked fire bricks, and the aggregate was coarse (up to a 1/4″). I used what I could and finished placing this layer of bricks. On Tuesday we are back into Kamloops and I will hopefully track down a more suitable mortar. Ironically, I had originally intended to make my own mortar as we have lots of clay, and access to clean, sharp sand. I did not want to make this job too complicated, so I bought mortar. The job already seemed hard enough!

The core of the stove is shorter than the unmortared version that I built. I will remove 2 bricks from the ceiling of the burn tunnel.