The type of mortar to use on old masonry repairs will depend on the condition of the existing masonry and the desired appearance of the repair. In general, it is best to match the type of mortar used in the original construction as closely as possible. This can usually be determined by examining the color, texture, and composition of the existing mortar.
If the existing mortar is in good condition and you want to match its appearance, you can use a pre-mixed mortar that is formulated to match the color and texture of the original mortar. If the existing mortar is in poor condition and you want to repair it with a different type of mortar, you can use a type N or type S mortar, which are both suitable for general purpose use in masonry construction. It is also important to use a lime-based mortar if the original mortar was lime-based, as this will help to preserve the historical integrity of the masonry.
How can I determine the condition of my mortar?
There are several factors to consider when determining the condition of brick mortar:
- Color: Is the mortar the same color as the bricks, or has it darkened or discolored over time?
- Texture: Is the mortar smooth and consistent, or is it rough and uneven?
- Composition: Is the mortar made from the same materials as the original mortar, or has it been patched with a different type of mortar?
- Cracks: Are there any cracks or gaps in the mortar joints?
- Deterioration: Is the mortar crumbling, flaking, or otherwise deteriorating?
To assess the condition of the mortar, it can be helpful to examine a few representative areas and then make a judgment based on the overall condition of the mortar. It may also be necessary to remove a small sample of the mortar for closer examination or to have it tested by a professional.
Do I need to add any additives?
It is generally not necessary to add additives to mortar when repointing, as long as the mortar mix is properly proportioned and the work is done correctly. However, in some cases, additives may be used to improve the performance or appearance of the mortar.
For example, an air-entraining agent can be added to the mortar to improve its freeze-thaw resistance, making it less prone to damage from repeated cycles of freezing and thawing. A water-repellent agent can also be added to the mortar to help prevent water from seeping into the masonry and causing damage.
If you are considering adding additives to the mortar, it is important to use them according to the manufacturer’s instructions and to consult with a professional mason or building conservator if you have any questions or concerns.