Getting to the Point
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Getting to the Point

Repointing is the process of renewing mortar joints in masonry construction. Over time, weathering and decay may cause voids in the mortar joints between brick masonry units, allowing the undesirable ingress of water.

Water entering through these voids can cause significant damage through freeze/thaw cycles, and from salt dissolution and deposition.

The Repointing Process

The repointing process begins by removing damaged pointing to a depth equal to or slightly more than the width of the joint, or to the point where sound mortar is reached. Depths greater than 2-1/2″ or 4 cm should be filled in several passes, allowing the mortar to cure for at least 24 hours. The joint profile should be as rectangular as possible, so the new pointing mortar has ample opportunity to bond with the masonry unit. Note that sound mortar usually does not need to be removed from a building during the repointing process, although it is a common practice.

Removal of old mortar between joints is done carefully to avoid damage to masonry units. On timeworn buildings with soft materials, such as under-fired brick, mortar removal by hand is often the most efficient way to prevent damage. Hard Portland cement mortar is usually removed with a grinder or power circular masonry blade, taking care not to damage the masonry units. Mortar removal from vertical joints is typically done by hand or with small power chisels.

Potential Problems

Poor repointing work often raises the level of the mortar joint above the face of the masonry unit, which causes the mortar edge to feather. Such a process is aesthetically undesirable and can cause erosion problems. Also, depending on the nature of the mortar, mortar that rises above the level of the face of the masonry unit can damage the corner of the masonry unit. In these cases, deteriorated mortar is not often removed to a sufficient depth.

Mortar Selection

It is essential that the types of mortar used for repointing have similar characteristics to the original mortar used in a building, including color and texture, permeability, compressive strength, and coefficient of thermal expansion. For example, if a soft lime-based mortar was used during the original building process, the most appropriate repointing material should also contain a large amount of lime. The use of Portland cement mortar for repointing older buildings with soft masonry units can cause significant damage due to physical incompatibilities.

An architectural engineering firm can perform a mortar analysis in order to make recommendations for replacement mortar that is both physically and aesthetically compatible with the building.

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