Mary's Grotto is a focal point and a serene place to worship at Benedictine University. Inspired by the Grotto at Notre Dame University, the project combines Old World craftsmanship and New Age technology. Its design mimics the natural grotto and Catholic shrine in Lourdes, France.
To imitate a small, natural cave, the project team used a method called silt casting. Once they poured the footings, with holy water from Lourdes mixed into the concrete, they formed a large dirt dome. The dome and a large wooden form became the stonemasons' guide to building the grotto's outer shell. They covered the dome with more than 40 tons of tumbled limestone, placing each piece by hand.
Before adding mortar, masons poured sand between the stones. The sand fell out once the dirt dome was removed, leaving an open, natural-looking joint. For reinforcement, the team attached steel rods to the back of the stone and added two cages of reinforcing steel around the dome.
When the dirt dome was removed, the stonemasons were finally able to see their craftsmanship in the exposed side of the stone. Mary's Grotto required 58 tons of stone and more than 1600 man-hours to complete.