Building a Chimney Flue 2

Click on the photos for a larger view

Vermiculite is a very lightweight, high temperature insulant. It is mixed with cement in a ratio of 6:1 to fill the void between the flue liners and walls. Use very little water to make the cement mix. Alternately, use Perlite - 10:1 with cement	The liners are built up - but don't go too far before filling the cavity with Vermiculite cement.
Eventually the structure emerges from the roof line.	The photos below show the start of a flue formed from concrete liners. These are larger than clay liners and are square in section.
The first concrete liner is bedded onto concrete lintels that are spanning the chimney breast.	In this build the liners were not surrounded by vermiculite cement - no need.
The concrete liners are stacked one upon another. The end result is the same - a gas tight flue.