Masonry, Repointing & Repairs
Re-pointing is the term used for repair of deteriorated mortar joints. This is done by removing any old, deteriorated mortar and replacing it with new. Re-pointing can be important to the continued sound physical condition of a building and has the potential to affect the appearance of historic masonry. The removal of deteriorated mortar should be undertaken only where absolutely necessary, where mortar is eroded or crumbling. Work should be performed using handheld, non-power tools, since power tools such as masonry saws have the potential to damage masonry units.
Complete re-pointing is seldom necessary, nor is it a good preservation treatment. New mortar should match the historic in strength, composition, color, texture and all other qualities. Prepackaged "masonry cements" generally contain large amounts of Portland cement, and produce a very strong mortar that can be damaging to softer historic bricks. If mortar analysis is no undertaken to determine the composition of the original mortar, the following soft, lime-rich mortar mix is appropriate for use on most historic masonry: 1 part white Portland cement, 3 parts Type S hydrated lime, 6 parts sand with no admixtures.
A color match should be achieved by using and appropriate colored sand to the greatest extent possible, since modern mortar pigments can weaken masonry if used in large quantities. Equally important is the appearance of the new mortar joints. New joints should match the historic in width, tooling, texture and profile. Special character-defining joints such as ?ruled? or ?grapevine? should be repaired or reproduced carefully.
Masonry materials may require repair as well as re-pointing. Appropriate techniques will vary according to the specific material. Damaged brick units are difficult to repair. If replacement is necessary, new units should match the existing in size, color, texture, and all other qualities. This can be done by using new or salvaged brick. Historic stone materials that are damaged should be treated carefully.
In keeping with the preservation Standards , the best approach is repair. Replacement should only be considered if the material is deteriorated beyond repair. Where cracked, spalled, or exfoliated, limestone, sandstone, marble, terra cotta, cast stone or concrete materials should be repaired to prevent further damage. The type of stone and the type and extent of damage should be determined before the repair method is chosen and the repair should be carefully executed to match the damaged material. Our office can provide information on appropriate specific treatments for historic masonry materials.