Tips for building a chimney on a pizza oven - Thermal expansion and expansion joint

Thermal expansion:

Most materials are subject to thermal expansion: a tendency to expand when heated and to contract when cooled.

Most Portuguese manufactures of wood-fired pizza ovens build their chimneys in direct contact with brickwork. We strongly do not recommend this procedure.

The force exerted on a chimney pipe or damper exerts tons of pressure ( stress ) on the steel as temperatures reach up to 1000 F  causing the steel to expand and cause structural cracks to the surrounding brickwork. 

Our ovens have built-in protection against the hazards of thermal expansion known as an expansion joint.

We separate the steel damper completely from the oven and it is loosely fitted over the chimney brick stub leaving space for the hot gases to expand. 

https://www.youtube.com/watch?v=NVkO1Dww1e8