This foam can be added to concreate to make.
Diy double wall stove pipe.
A major issue with these is a loss of heat or having it misdirected.
The double wall pipe is used if the gap is less than 18.
The pipe should fit the outlet or exhaust of your wood burning stove.
In this measurement reduce the length at least by two inches as the 90 degree elbow is about 8 inches tall.
The stove pipe is connected to the stove and goes through the ceiling or back of the home to redirect smoke outside of the home.
Darwin invented the foam mate which is a machine that creates a nice thick foam the consistency of shaving cream.
The double wall allows a clearance of 6 from the wall and 8 from the ceiling.
The homemade triple wall chimney pipe you are considering could work for a while in principle but i strongly advise against your trying it.
Your worries about the durability of galvanized steel.
Once the gauge of the pipe is determined next step is to measure the length of the sheet required to make a pipe from the stove s exhaust to the chimney flue.