When you choose to conduct chimney repair on your own, there are many details to consider. One of these details, which you will come across during tuckpointing or brick repair, is the exact mix of the mortar used to stick the bricks together. It is often impossible to find the exact brand of mortar mix used during the original construction of your chimney, so you have to take care mixing the new mortar to exact specifications.

What Considerations Should I Make Before Mixing Up a New Batch of Mortar for Brick Repair?

There are several, including:

• Mortar Strength – Mortar made nowadays is not the same as the mortar made in the past. Modern mortar is stronger, more durable, and composed of tighter chemical bonds. When up-to-date mortar is spread in the joints of a chimney that is partly made up of older and weaker mortar, it can throw off the load factors by placing more weight on certain bricks (the ones covered by the old mortar) than others. This can easily cause bricks to deform or even break, an event that will likely lead to a chain reaction, destroying the chimney.
• Mortar Colour – As you can imagine, the exterior appearance of a chimney loses a significant amount of its charming allure if half of the lines of mortar running between its bricks are cream-colored and the other half are pure white. This is why it is of utmost importance to carefully match the color of any new mortar to the exact color of the old mortar. You may have to get creative with masonry coloring to match a mortar that contains unusual tints.
• Mortar Durability – Mortar is traditionally a mix of 1 part cement, 1 part lime (as in limestone), and 6 parts sand. Most mortar does not stick to this formula exactly, however, and even a slight differential in a mortar’s formula, like 1.05 parts lime instead of 1, can make a substantial difference in its durability. And we probably don’t have to spell out for you what will happen if parts of your chimney’s mortar structure corrode at a faster rate than other parts. Hint: it ends in a collapsed chimney.

Mixing mortar to the exact specifications put forth by your old mortar can be a nightmare, but the highly-trained brick repair and tuckpointing experts at the Toronto-based Cummins Restorations are happy to help.