Chimney lining is the most important piece of the chimney. It is the part that protects the chimney from overheating or catching fire. Popular liner materials are aluminum and stainless-steel. Though metal and stainless-steel liners often last long, over time sulfur and water mix inside the chimney, and the mixture starts to corrode the liner resulting in the liners pulling away from the framing and walls.
Before the 1900’s clay tiles were the quality. Masonry chimneys were tested by the National Bureau of Standards (NBS) throughout the Nineteen Eighties. Before the 1900s chimneys were lined with mortar. It had been determined that any unlined chimney would be extraordinarily unsafe to use.