When it comes to repairing old masonry, the choice of mortar is critical and should be based on the existing masonry’s condition and the desired repair outcome. Ideally, you’ll want to closely match the type of mortar originally used in the construction. This can typically be determined by scrutinizing the color, texture, and composition of the existing mortar.

1. Assess the Existing Mortar

Before diving into your masonry repair project, you need to evaluate the condition of your existing mortar. Here are some key factors to consider:

a. Color:

Is the mortar still the same color as the bricks, or has it darkened or discolored over time?

b. Texture:

Is the mortar smooth and consistent, or does it appear rough and uneven?

c. Composition:

Is the mortar made from the same materials as the original mortar, or has it been patched with a different type?

d. Cracks:

Are there any noticeable cracks or gaps in the mortar joints?

e. Deterioration:

Is the mortar crumbling, flaking, or displaying signs of overall deterioration?

By examining these aspects across a few representative areas, you can form a judgment about the mortar’s overall condition. In some cases, it might be necessary to remove a small sample for closer examination or professional testing.

2. Choosing the Right Mortar

Depending on your assessment, you’ll have different options for mortar selection:

a. Matching Existing Mortar:

If your existing mortar is in good condition, and you want to maintain the original appearance, consider using a pre-mixed mortar specifically formulated to match the color and texture of the original mortar.

b. Repairing with Different Mortar:

If the existing mortar is in poor condition and you’re opting for a different type of mortar, options like type N or type S mortar, suitable for general-purpose masonry construction, can be used. It’s essential to switch to a lime-based mortar if that was the original type, as it preserves the historical integrity of the masonry.

3. Consider Additives

While it’s generally not necessary to include additives in mortar for repointing, there are instances where they can enhance performance or appearance:

a. Air-Entraining Agent:

Adding an air-entraining agent can improve freeze-thaw resistance, making the mortar less susceptible to damage from freezing and thawing cycles.

b. Water-Repellent Agent:

To prevent water from infiltrating the masonry and causing harm, you can add a water-repellent agent to the mortar mix.

Should you decide to use additives, it’s crucial to follow the manufacturer’s instructions meticulously. If you have any doubts or concerns, consulting a professional mason or building conservator is advisable.

In conclusion, the success of your old masonry repair project hinges on thoughtful mortar selection based on the existing conditions and your restoration goals. By carefully assessing the mortar and making informed choices, you can preserve the integrity and beauty of your historic masonry for years to come.