For homeowners

Types of brick: which repointing mortar suits each one?

Choose Hard-cored brick for mortar O, N or S, for sheltered, moderate or severe exposure (NPS, 1998); Molded brick for mortar K, O or N, for sheltered, moderate or severe exposure (NPS, 1998); Soft hand-made brick for mortar "L", K or O, for sheltered, moderate or severe exposure (NPS, 1998).

The right choice depends on how durable the brick is: hard-cored, molded or soft hand-made and how exposed the wall is to weather: sheltered, moderate or severe.

How we know: By InstaBids editorial team with AI research agents. · Sources read: 22 October 2026 · Updated 27 October 2026

Repointing is the process of removing deteriorated mortar from the joints of a masonry wall and replacing it with new mortar (NPS, 1998). The mortar letters come from the table of suggested mortar types for different exposures in the National Park Service brief Repointing Mortar Joints in Historic Masonry Buildings.
Type	Best for	Main advantages	Main drawbacks
Hard-cored brick	mortar O, N or S, for sheltered, moderate or severe exposure (NPS, 1998)	the National Park Service classes hard-cored brick with granite as very durable masonry (NPS, 1998)	no official source names one
Molded brick	mortar K, O or N, for sheltered, moderate or severe exposure (NPS, 1998)	the National Park Service classes molded brick with limestone and durable stone as moderately durable masonry (NPS, 1998)	no official source names one
Soft hand-made brick	mortar "L", K or O, for sheltered, moderate or severe exposure (NPS, 1998)	no official source names one	the National Park Service classes soft hand-made brick as minimally durable masonry (NPS, 1998); soft brick with a relatively high permeability needs a soft, high lime mortar (NPS, 1998); power tools used by unskilled masons can be disastrous for soft brick (NPS, 1998); soft, incompletely fired brick from the 18th and early 19th centuries may have become so porous that it needs paint or some type of coating (NPS, 2000); in one wall the brief shows, a mortar less permeable than the soft bricks caused severe damage (NPS, 1998)

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Sources for the facts on this page

U.S. National Park Service, Technical Preservation Services, Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings (October 1998), government, read 22 October 2026.
U.S. National Park Service, Technical Preservation Services, Preservation Brief 1: Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings (November 2000), government, read 22 October 2026.