Historic Masonry Info

It’s just a few more weeks until winter is over and the outdoor projects begin again. Masonry repointing is on many of our to-do lists. Before you begin a repointing project or hire a professional mason, do your home and your wallet a favor and make sure you’re using the right kind of mortar. I know it sounds trivial, but a simple mistake here can permanently damage brick and stone.

How can mortar damage brick and stone? First, it can be too strong – so strong that under the pressures experienced during normal temperature changes, the surrounding brick or stone will crack while the mortar remains steadfast. Mortar must be soft enough to crack first and act as a sacrificial element in order to preserve the integrity of brick and stone. It’s one thing to repoint a building or foundation, but replacing multitudes of damaged handmade bricks or hand-cut stones is a much bigger issue. The second problem with some mortars is that they are so impermeable that moisture cannot escape from masonry walls. In this case, moisture can push its way through your bricks and cause a kind of damage called “spalling.”

Living in Bethlehem, we’re all very familiar with our locally-mined Portland cement. Portland cement is a fine product with many practical uses, but it may be too hard and/or not permeable enough for repointing historic masonry. Often, a much better alternative is traditional lime mortar. Lime mortar is soft enough to preserve brick and stone yet strong enough to serve as an effective mortar. In addition, lime mortar has self-healing properties. In other words, any small cracks that form will often repair themselves as water transports and deposits lime in compromised areas. And, if using environmentally-friendly materials is important to you, lime mortar has a much lower carbon footprint than some other alternatives.

If a masonry project is on your to-do list, I encourage you learn more about lime mortar. One word of caution: the internet is full of misinformation about mortars for historic structures. A reliable, local source of information, and retailer of lime needed to make lime mortar, is deGruchy’s Limeworks in Quakertown, PA, www.limeworks.us.

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