Chimney Restoration usually refers to structures built prior to the mid-1900s. It is unusual, prior to that time, to find chimneys that were built with liners or with two layers of masonry.
The mortar of unlined and single wall chimneys dehydrates with repeated use, loosening the bond between brick or stone. This weakening can result in holes between the brick or stone or in their actual collapse into the interior of the chimney. It is not unusual to find the internal divider or wythe walls partially collapsed or missing in chimneys built prior to the use of lining systems or to the addition of Portland to the mortar.
Heat transfer in such structures is also of concern. The heat from chimney fires or overheated furnace systems can actually transfer through a single course of a historic masonry chimney and ignite combustible material adjacent to it. As wood ages, a process called pyrolysis takes place and the combustion point of wood is lowered, making older structures more prone to damage.
A pumped masonry lining system is often the best choice in restoring a chimney to functional usage. The insulated masonry liner bonds with the original materials, providing a fireproof barrier between flue heat and combustible material. The Golden Flue lining system is approved for 0 ” clearance to combustibles, exceeding modern Building Code.
A pumped masonry liner also returns structural integrity to the chimney. Voids are filled, cracks sealed and the bond between brick or stone is reestablished on the inside of the chimney. The final result is often better than original construction.
Some chimney professionals strongly advocate the use of pumped masonry linings in almost all applications. They often guarantee proper draft of a fireplace or appliance, even if the resulting flue size is smaller than original. Insulated, round, smooth flues draw much better than any other configuration.
It is usually possible to restore a chimney without disturbing the exterior. Most chimney restoration in clearing blockages and opening flues is accomplished from the inside. Historical chimney restoration of structures need not look like a patchwork of repairs.
Chimney top dampers often complement the installation of liners. These reliable inventions completely seal the chimney at the top but are fully operational from the fireplace opening. They are usually unseen from the ground and eliminate the need for caps.
Tuckpointing open mortar joints is occasionally required. Frequently used is a ‘soft’ mortar with attention to matching the original color of mortar and brick.
Waterproofing may further extend the life of exposed masonry. A product designed specifically for use on chimneys should be used. Waterproofing repels moisture while allowing the structure to breathe. It is also UV stabilized and leaves the exterior appearance of the chimney largely unchanged in color or texture.
For a complete description of the pumped masonry lining process and for some comparisons of the advantages of choosing pumped masonry over stainless steel, go to Pumped Masonry.