Brain Food: Crumbling Gargoyles
One of Flagstaff’s oldest and most beautiful churches is the Gothic Nativity of the Blessed Virgin Mary Chapel.
It was built in 1929 in the city’s downtown area and is known for its many decorative gargoyles. But those features are falling apart, not because of the church’s age, but because of chemicals in the volcanic material that was mixed into the concrete. Carolyn Searls is a civil engineer.
“The most noticeable deterioration on the chapel is cracking and crumbling of the pre-cast concrete. Many of the gargoyle’s heads are missing. The worst damage is at the top of the tower where approximately 75 percent of the blocks are cracked. At least one piece has fallen from the tower to the street,” she says.
Searls says the microcrystalline silica in the locally mined volcanic rhyolite and dacite is reacting to the concrete’s alkalinity. She and her masonry restoration team are using a laser scan of the outside façade to produce drawings and design repairs. Some features, like the gargoyles, will have to be replaced.
“An important consideration is that the shape and texture of the new pieces matches the original. This is done by making molds of the most intact remaining pieces. A model is then cast from the mold,” she says.
The Nativity of the Blessed Virgin Mary Chapel is listed on the National Register of Historic Places for its architectural significance. The restoration project is expected to take a couple of years and more than $2 million to complete.