I once overheard a colleague of mine describe the process of deteriorating mortar as “romantic decay”, I guess all the years of his travels throughout Europe and the Scandinavian countries he had seen his share of crumbing bricks and mortar and had become un-alarmed about the condition. Interestingly enough, it seems the opposite is true here in the United States. We tend to get all worked up about crumbling mortar, especially the condition when the material turns to sand in your hand when you rub on it vigorously between the brick.
But according to the Preservation Briefs 2, “Repointing Mortar Joints in Historic Masonry Buildings” describe a different view of a good working replacement mortar. In fact, the mortar could be called a “romantic decaying mud” depending on how you look at it.
Here is what Brief 2 has to say about repointing mortar. “In creating a repointing mortar that is compatible with the masonry units, the objective is to achieve one that matches the historic mortar as closely as possible, so that the new material can coexist with the old in a sympathetic, supportive and, if necessary sacrificial capacity.” We have mortar all over this country trying to sacrifice itself for the good of the masonry units by falling apart in historic masonry walls!
But unfortunately, we also have many engineers and architects, building owners and contractors doing their best to prevent the process from occurring. When the romantic decay is identified the sure tell remedy is usually a stronger mix design one that contains a large amount of portland cement to go back in with during the repairs. A new mortar without the romance and certainly no sacrifice.
As we continue our work on important historic masonry structures lets – let the mortar help us to identify the real problems – usually the water infiltration somewhere, somehow. Blame the water not the historic romantic mud!