Because a Rocket Stove pushes gas along the exhaust flue, there will be pressure inside trying to squeeze gas out through any cracks. During combustion there may be Carbon Monoxide and Nitrogen Monoxide present in the fumes. Both gasses are toxic so any exposed metal pipe inside the building should be thoroughly sealed to make sure no gas can escape. In the bench above the whole flue is sealed with cob (sand, clay and straw). Follow the picture back to www.naturalhomes.org to find out more.