Finding the Right Mortar Match in Denver: Brick Repair Denver's Guide to Successful Repointing

When it comes to preserving historic buildings in Denver, finding an appropriate mortar match is critical. Repointing, the process of renewing the external part of mortar joints in masonry restortion and preservation, must be done with careful attention to the building’s original materials and design. The wrong mortar choice can cause serious damage to the structure by being too strong or too impermeable to moisture. Here’s what you need to know to ensure your repointing work is both physically and visually appropriate for your building.

Do Your Research
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Before starting any repointing work, it’s essential to research and analyze the existing mortar and masonry materials. By examining unweathered portions of the historic mortar, you can determine the appropriate mix for your new mortar. This is important because new mortar must not be stronger or less permeable than the original to avoid damaging the building.
Take time to examine the masonry units themselves—whether brick, stone, or terra cotta—and understand the original construction techniques. A simple, non-technical evaluation of the masonry and mortar can reveal valuable information about the strength and permeability of both. This helps ensure that the new mortar will blend with the original in both function and appearance.

The Role of Mortar Analysis

For masonry buildings of special historical significance, it might be beneficial to have a qualified masonry contractor who can conduct a mortar analysis. While this can help identify the ingredients of the original mortar, it’s not foolproof. Factors such as the original water content, curing rate, and even the weather conditions, especialy in Colorado, during construction can’t be determined by lab results alone. The most helpful information from laboratory mortar analysis is often the identification of the sand used—its gradation and color—which is critical for achieving a good color and texture match in the new mortar.

Matching the Historic Mortar

When creating a repointing mortar, your primary goal should be to match the historic mortar as closely as possible. This ensures that the new material will coexist with the old in a harmonious way. The following criteria should be met for a successful match:

• Color, texture, and tooling: The new mortar must match the historic mortar in all of these visual aspects.
• Sand: Sand is the largest component of mortar and has a significant impact on the color and texture. It’s important to match the sand from the original mortar.
• Vapor permeability and softness: The new mortar should be softer (in terms of compressive strength) than the masonry units and must be as vapor-permeable as, or more permeable than, the historic mortar. This prevents stress from being transferred to the masonry units, which could cause damage like cracking or spalling

Why Mortar Strength Isn’t Always a Good Thing

A common misconception is that stronger mortars are better. In reality, when repointing historic buildings, the mortar should be softer and more permeable than the masonry units. This is because stresses within a wall—caused by expansion, contraction, or moisture migration—need to be relieved by the mortar, not the masonry. A mortar that’s stronger than the masonry will force these stresses onto the masonry units, potentially causing irreversible damage. High lime mortars, though often softer, allow for higher permeability and can accommodate the building’s natural movements over time. So, stop using Type S and high cementitious cement fro repoinitng on historical brick and stone buildings in Denver.

The Components of Mortar: What You Need to Know

The main ingredients of mortar are sand, lime, water, and sometimes Portland cement. Each plays a crucial role in the mortar’s properties.

• Sand: This is the most important ingredient when it comes to matching the original mortar’s color and texture. The sand should be free of impurities and carefully graded to match the original mortar as closely as possible.
• Lime: Historically, lime was the primary binding material in mortars, offering excellent plasticity and permeability. Lime-based mortars are ideal for historic structures because they allow the building to breathe and accommodate natural movements. High calcium lime, used historically, is still a good choice for many repointing projects today.
• Portland Cement: In 20th-century mortars, Portland cement was often added for additional strength. However, excessive Portland cement in a repointing mortar can make it too hard and impermeable, leading to damage in softer historic brick or stone. If used, it should be carefully balanced with lime to ensure the mortar remains compatible with the masonry.

Modern Additives: Use with Caution

While modern chemical additives can be helpful in certain situations, they aren’t always appropriate for historic masonry. For example, air-entraining agents can improve resistance to freeze-thaw cycles, but other additives, such as antifreeze compounds or bonding agents, can introduce new problems like efflorescence or poor bonding to the masonry. It’s best to avoid unnecessary chemicals and instead focus on proper mortar composition and joint preparation.

Conclusion

In repointing historic buildings in Denver, the goal is to create a mortar that works in harmony with the original materials. Whether you’re restoring a century-old home or a landmark building, understanding the composition and role of mortar is key to maintaining the structure’s integrity. With careful research, analysis, and attention to detail, you can ensure that your repointing work not only protects the building but also preserves its historical beauty for generations to come.

If you'd prefer to hire a specialist in masonry restorartion, to ensure your historic building is repointed with the proper mortar, reach out to Brick Repair Denver 720-445-9474