Calcium Silicate Boards are high heat, commercial grade insulating boards. Both the Primo and Mezzo are made from an insulating aggregate, meaning the oven will retain heat for well over 4 hours without adding fuel to the fire. To ‘build your oven in’ or to boost your ovens heat retention to well over 24+ hours, insulate the oven floor with calcium silicate insulation board. Do I need Calcium Silicate Insulation Board? – ask the Stone Bake Team The boards are £50 and are suitable for Primo or Mezzo installation.