Biggest Mistake When Tuckpointing Older Brick Homes
Older brick homes have withstood many forces of nature. Temperature fluctuations cause the brick to expand and extract. After many years of aging the mortar joints begin to deteriorate. Tuckpointing or repointing when done correctly restores the home’s physical integrity as well as its visual appeal.
Improper mortar mixture is the biggest mistake made when tuckpointing older brick homes. Such a mistake can damage a brick home. Ironically, too strong of a mortar mixture can be harmful. That’s because in old homes (pre-1890) the bricks were weaker and mortar was used not as a glue to hold brick together but as a joint to absorb moisture and allow brick movement. The mortar should be as soft or softer than the original because it will absorb water and act as an expansion joint allowing the wall to give, relieving stress. It is important to get it right to prevent damage. The amount of Portland Cement in a mortar mix can determine its softness or hardness.
Fortunately, a visual inspection by an experienced tuckpointer can provide most of the information needed to use the right mortar mix. He should assess the strength and permeability of the existing mortar. The mortar mix doesn’t have to contain the exact mix as that used in the original. In fact, that would be impossible. The goal is to come close so that old and new mortar co-exist and match closely.
Historically, bricklayers used lime and sand to mix mortar. It is the sand in the mixture that influences color and texture. Vapor permeability is another critical factor. It’s a measure of how much water vapor passes through the mortar. In older brick homes the new mortar should be as vapor permeable and as soft as the old mortar. This prevents damage to the masonry by relieving stresses to the wall. Careful attention to these mortar attributes helps prevent premature cracking of the mortar and spalling brick.
A narrow tuck-pointing trowel may be all that’s needed to scrape the fresh mortar into a joint of an older brick home, but it is an experienced tuckpointer’s observation, along with a spray mister, that keeps the mortar moist and prevents early drying.