Chimney repointing is the process of removing degraded mortar from the joints of a masonry chimney and replacing it with new mortar. If done well, the chimney’s structure will be strengthened and its lifetime extended. If done incorrectly, the chimney’s structure will be compromised and its appearance will be marred.
When a chimney’s mortar is cracking, missing, or deteriorating, chimney repointing will need to be done. If neglected, water from the outside will penetrate the chimney’s wall. As the water undergoes freeze-thaw cycles over an extended period, it expands and contracts, leading to the deterioration of the masonry. The water can also facilitate the process of efflorescence in which salts are crystallized and cause the masonry to degrade as a consequence. If the salts crystallize beneath the chimney masonry’s surface, the process is called sub-efflorescence or crypto-florescence.
Chimney repointing will need to be performed as well if the masonry has been repointed incorrectly in the past. The mortar in the repointed area may not match, it may be too hard, or it may not allow water vapor to escape, which is causing the masonry to crumble, etc.
It is critical that the correct mortar mix is used as most chimneys need a specific custom mix that is designed for their masonry units. This mix should be designed and customized by a licensed, insured, knowledgeable, and experienced chimney mason.
To ensure that the chimney repointing project is properly performed, the mortar joints to be repaired must first be prepared to accept the new mortar. When the appropriate mortar recipe has been selected for the chimney, it must be mixed properly. The process will depend on the recipe. Suction, or the transfer of water from the wet mortar into the masonry, must be controlled as the new mortar is applied. The correct tools and procedures must be observed to ensure the mortar is firmly compacted into the mortar joints. Curing conditions for the mortar like sunlight, temperature, humidity, and wind must be controlled as much as possible after the mortar has been applied. Lastly, the more complicated the project, the more likely a trained and experienced mason will need to be hired.
Chimney repointing is critical to maintaining a chimney. Without it, a chimney will degrade and break down before its time.
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