Beware of Choosing an Incompatible Pointing Mortar for Sandstone (or any stone for that matter)
It’s painful when I see a building with severe stone damage caused by a poor mortar choice. I spotted a prime example while walking past a brownstone property in Manhattan.
As a type of sandstone, brownstone requires a softer pointing mortar that can expand and contract with freeze/thaw cycles. This avoids putting pressure on the surrounding substrate. When you use a mortar with a PSI greater than the substrate, the substrate will fail during freeze/thaw cycles. This damage can be irreversible, with the only option of cutting out the too-hard pointing mortar, patching and resurfacing the substrate, and then repointing with the appropriate pointing mortar. This is essentially a full restoration — a major expense.
A brownstone in Manhattan with severe stone damage caused by a poor mortar choice.
Always select softer mortar that’s compatible with the stone..
To avoid this problem, I always recommend selecting a softer mortar that’s compatible with the stone and color-matching it to the varying shades of the substrate. For the building pictured here, our M110 historic pointing mortar with a sandstone base would be ideal. Like all our mortars, M110 is engineered to be completely compatible with the specific masonry substrate and without any bonding agents (a/k/a polymers, glue, rubber, etc.). And the bonus of having no bonding agents is that you can point in a single lift—no matter the depth.
More questions? Contact me at tech@cathedralstone.com. I’ll answer any questions and help get you a sample to review.
