A common maintenance task for brick masonry is repair of mortar joints. The longevity of mortar joints will vary with the exposure conditions and the mortar materials used, but a lifespan of more than 25 years is typical. The longevity of brick, however, may well exceed 100 years. Consequently, occasional repair of the mortar joints is expected over the life of the brick masonry. It is our observation that the most common reason for repointing brick masonry is to improve water penetration resistance. Repointing deteriorated mortar joints is one of the most effective and permanent ways of decreasing water entry into brickwork. This is because the most common means of water entry into a brick masonry wall is through debonded, cracked or deteriorated mortar joints.
How to Choose your repointer
An important step toward a successful repointing job is to secure a qualified and experienced repointing craftsman. An individual who is an excellent mason/bricklayer may not be a good repointer. It is suggested that skills be substantiated by prior repointing projects or by prequalifying. One method of evaluating craftsmanship is to designate an inconspicuous section of the brick masonry and permit candidates to place a sample of their work on that section of the masonry. The skills in question are: (1) cutting out the mortar joints to the proper depth and profile with minimal damage to adjacent brick units (2) proper preparation of the mortar for repointing, (3) proper placement of mortar by layering, compacting and tooling, and (4) accurate color matching to adjacent, original mortar joints. Cleanliness of the repointing operation is also important, so that extensive cleaning of the finished wall is not necessary.
What to Repoint
A critical step in the repointing operation is to identify wall areas which require repointing. This step is critical be cause only defective joints require repair, repointing is very labor-intensive work, and original mortar joints in good condition are preferred over repointed mortar joints. Conditions which may require repointing include: (1) mortar erosion more than 6 mm, (2) crumbling mortar, (3) hairline cracks in the mortar, and (4) cracks between the brick and mortar. Visual observation in combination with light scraping with a metal tool can detect cracked, spalled and crumbly mortar joints. This is the most common means of determining areas to be repointed. On older buildings, "cleaning" by low or moderate pressure water wash (not grit or chemical wash) may be required to evaluate the condition of mortar joints. Consult Technical Notes 20 for proper water washing techniques. It must be emphasized that, in this case, the purpose of cleaning is not to get a new looking building.
To avoid irreparable brick damage, the compressive strength of the repointing mortar should be similar to orweaker than the compressive strength of the original mortar. Under load, a stronger repointing mortar will deform less than a weaker original mortar, causing the load to be concentrated on the thin strip of stronger repointing mortar. This stress concentration can lead to spalling of the brick face. The brick masonry is loaded by its self-weight and any externally applied loads present. In addition, the brick masonry is subjected to internal loads due to its thermal expansions and contractions and the shrinkage of the repointing mortar.