Mortar is the glue that holds bricks, stone, and other masonry units together. Choosing the correct mortar for your historic restoration project can help ensure the long-term success of your build. The correct mortar should closely match the type of mortar used in the original construction of your masonry building. However, other factors must be considered when determining the right mortar type for your restoration project.
Moisture Resistance
Mortar provides moisture resistance, which is crucial to a successful masonry project. Mortar helps keep bricks, stone, and concrete blocks in place as a unified structure by bonding them together. In addition, it prevents the movement of individual masonry units and absorbs and distributes loads and stress. It’s essential to choose the correct mortar for your historic masonry restoration project based on the existing condition of the masonry and the desired repair outcome. Generally, the mortar type should closely match the original and be compatible with masonry materials. When choosing a mortar for your project, look at its durability, bond strength, flexibility, and moisture resistance. Additionally, consider the engineering specifications or design requirements for the project. For example, if your project requires load-bearing walls or structural elements, you must choose a mortar with high compressive strength.
Flexibility
Different masonry projects have varying strength requirements that need to be met. Consult with experts in masonry construction to assess the project needs and guide your mortar choice. The type of masonry units and their porosity must be considered when choosing a mortar type. Highly porous materials may require a mortar with higher moisture resistance and better workability. Compressive strength also needs to be considered. If a mortar is too strong for its installed material, it can crack or be worn away during freeze-thaw cycles. Choosing a mortar with a lower compressive strength than the installed material is best. Mortar can be tinted in various colors to match or contrast with the installed masonry units. This helps to create a more visually appealing result. For example, some masons prefer to tint the mortar they use for real stone veneer to match the natural color of the stones.
Compressive Strength
Mortar is the glue that holds brick, stone, and block units together to function as a unified construction. It also helps to distribute loads, absorb stresses, and protect against environmental factors like weather changes and moisture. Different projects will require varying levels of strength in mortar. Engineering specifications and design criteria can help determine minimum strength requirements for a given project. Regardless of what specific mortar mix you use, choosing a strength level appropriate for the project you are working on would be best. This will prevent premature deterioration and failure of the masonry materials. Typical mortar mixes include Type N, Type O, and Type S. Each mix has a different proportion of cement, sand, and water to provide various results. The lowest strength is Type O, often used in interior masonry or repointing brickwork. Higher strength options are available for load-bearing walls and increased resistance to free-thaw deterioration.
Color
When repairing old masonry, it is often essential to closely match the color of existing mortar. This can be accomplished by examining the existing mortar for color, consistency, and texture. It is also an excellent practice to pre-dampen masonry units consistently throughout a project to control the rate of absorption and moisture, which can significantly impact the final appearance of the repaired masonry structure. Many mason contractors utilize a reference-colored mortar channel kit assembled by a pigment company. While these channels may provide a good approximation of a brick wall’s appearance, they can be misleading as to the actual color of a mortar joint. Mortar makes up between 7% and 20% of a wall’s surface, so selecting a contrasting mortar color can dramatically change the look of your home. Whether you want your masonry to blend in or stand out is a crucial consideration often overlooked.
