Mortar and Longevity: Will Our Buildings Stand the Test of Time?
Did you ever look closely at the exterior of brick or stone home, and see hairline cracks running up the wall? Or sometimes the mortar joints have lots of cracks running across them, so that the mortar looks like it could fall out in 3-inch sections. Even an old (or not so old) concrete block building, like a garage, can have joints cracking out all over the place.
Natural Hydraulic Lime Mortar
Whether your a homeowner, or someone in the building trades, you may have noticed mortar joint failure, and maybe you had a thought like, "What is going on here? I thought masonry was the best exterior-supposed to last forever!!!"
Isn't a stone home supposed to last forever?
What about the castles in Scotland and the palaces in Prussia??
We are stonemason's, and these are questions we have started to ask also. For us, our livelihood depends on the answers because we can already see cracked mortar joints in work we did 5 years ago! Could the mortar that we were trained to mix and use be flawed?
Why do patios and sidewalks crack so quickly-often in less than 10 years? Why does almost every stone, brick, or block building show cracks in just a few years after it's built? That's not the longevity we expect from using such historic and time-tested materials!
Materials scientists have been asking these same questions. After studying those castles in Scotland and masonry buildings all over the pre-modern world, the answers are starting to come out. Turns out the mortar we use today is not at all historic. Time has tested it, and it is failing the test.
A little construction history might help at this point. For at least 7,500 years, man had been using (roughly) the same process to make mortar: burn high-calcium limestone by layering wood and stones inside of a really fat chimney (kiln) and then lighting it on fire. The resulting burnt stones are then crushed and mixed with sand and water to make mortar. The burnt lime reacts with the water, causing it to get sticky and then harden, lasting for centuries or longer in between the stones in a wall.
This lime is called hydraulic lime because it hardens without the presence of air. Getting hard is a chemical reaction that is different from just drying out. It will get hard under water.
Now don't confuse hydraulic lime with hydrated lime. Hydrated lime is a different process, a different material altogether. Hydrated lime can't be used as the binder in mortar because it never gets hard. Hydraulic lime does.
Now, jump forward in the history of mortar to the late 1800's when various inventors began experimenting with new processes and materials for making cement. Portland cement, the almost exclusive binder and hardener in today's mortar, concrete and stucco. It got its name from the Isle of Portland in the English Channel where limestone had been quarried for centuries and admired for its building qualities. By 1878, the British government had issued a standard for Portland cement, and in 1907, production began in the United States. It came to be the main ingredient in mortar and concrete throughout the country by the end of World War II.
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