Why Compatible Mortar is Crucial For Historic Masonry Restoration
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Why Compatible Mortar is Crucial For Historic Masonry Restoration

As part of the exterior restoration of the African Meeting House in Boston's Beacon Hill section, Abbot formulated special mortar compounds to match the composition and color of the original mortar to meet historic guidelines.

As part of the exterior restoration of the African Meeting House in Boston’s Beacon Hill section, Abbot formulated special mortar compounds to match the composition and color of the original mortar to meet historic guidelines.

When it comes to historic masonry restoration, selecting the appropriate mortar for the type and strength of a building’s brick is crucial to the durability and longevity of the structure. Here are several reasons you’ll want to be sure the most compatible mortar is used before you are left with an even bigger and more expensive problem on your hands.

Brick Strength

The strength of brick masonry is an important factor when choosing an appropriate mortar for an historic restoration project. Historic brick is much softer than modern varieties, and can break and deteriorate if a much stronger mortar is applied. Modern brick is much stronger due to the use of high temperature firing processes that were not available in earlier times, and should be considered for any historic masonry restoration project.

Portland vs Lime Mortars

Aside from the brick strength, the type of mortar itself can play a big part in the success of an historic restoration project. Portland cement mortar was not introduced until 1871, and is one of the most common mortar types used today. However, while portland mortar is quick-setting, strong, and inexpensive, it is also more rigid and less permeable than previously used lime mortar. If portland cement mortar is used on historic brick, it can cause unwanted damage and deterioration to the brick structure, resulting in additional repairs, restorations, and costs.

Water Permeability

Last, but not least, is the difference in water permeability between portland and lime mortars. Lime mortars are designed to absorb and release water between joints. Portland mortars, on the other hand, are designed to create a waterproof seal. If used inappropriately, portland mortar can cause water to become trapped and forced to escape through the brick masonry. This can lead to brick protrusion, and ultimately damage and deterioration.

For further information regarding historic masonry restoration, contact Abbot Building Restoration at 617-445-0274.

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