Casting the flue gallery

[david s]

I hope these pics answer your questions. In my build the gallery is joined to the inner dome with a small (8 to 10 mm) gap between the gallery and the outer decorative arch with the gallery and dome insulated. This works pretty well as the cast gallery is relatively thin and therefore not too much of a heavy thermal mass acting as a heat sink. Brick builders using much thicker bricks for the gallery sometimes leave a gap that they insulate between the dome and gallery because there is an enormous mass in the gallery that acts as a heat sink sucking heat from the dome. I use 5:1 vermicrete packed in between the cage and the pipe, then a 35mm layer of 10:1 vermicrete over the blanket
layers

[frank1985]

david s Amazing... Sorry if this is a silly question, but is the cage strictly just to keep the Vermicrete in place till it dries, or do you render directly over it as well for added reinforcement? In the case of the latter is there a particular type of wire (stainless steel, galvanised wire etc.) that will work best?

[david s]

The cage remains in place. On a tear down of my 8 year old mobile oven that needed replacement there was no sign of corrosion. I was surprised. I use aluminium insect screen surrounded by galvanised bird wire. It does a number of things, being sufficient to contain the mix and hold the base of the pipe in position. as well as allowing moisture to pass through and to provide structure and strength to the outer rendered shell.