Lime Mortar Repointing or Tuckpointing
Mortar is the expendable or sacrificial element in a masonry building. Like tires on a car, mortar is meant to wear away over time. Because it erodes, lime based mortar needs to be replaced (repointed) periodically to retain the soundness of the structure it protects. In buildings built traditionally with lime mortar, this repointing is required about once every 100 years or as needed because of specific damage.
Restoring masonry with a mortar that matches the history of the building is critical in maintaining the health and beauty of the building. Older bricks are softer than bricks made today. If a mortar containing Portland cement is used to repoint, the masonry can be damaged during freeze/thaw cycles. Historically, mortar consisted of lime and sand or sometimes clay, natural materials that were local to the construction site and reasonably durable. These are the materials with which most historic buildings (built before 1940) should be repaired.
Attributes of Lime-Based Mortar:
~It’s vapor permeable, allowing excess moisture to evaporate. This avoids mold generation and ensures that the bricks won’t crack or break during freeze/thaw cycles.
~It has less compressive strength than cement, becoming a buffer between the bricks like cartilage in a human joint. As the bricks move and settle, the mortar shifts to accommodate the changes, keeping the bricks intact.
~It has a higher bond strength than cement. A better bond protects from seepage and erosion.
~It is historically appropriate. When repairing a historic structure, it’s important that the new visually match the old as much as possible.
~It is self-healing. Lime-based mortar can close cracks by dissolving small bit of lime mixed with rain, further protecting the building from water intrusion or more dramatic damage to the mortar.
~Lime-based mortar is a “green” product, made entirely from and by nature.