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HomeContentMAPEI mortar brings life to National Shrine’s mosaic dome in Washington, D.C.

MAPEI mortar brings life to National Shrine’s mosaic dome in Washington, D.C.

MAPEI’s Kerabond/Keralastic System was used to install 14 million pieces of specialized Venetian glass tile 

The Basilica of the National Shrine of the Immaculate Conception in Washington, D.C., is the largest Roman Catholic church in the United States, and the second largest church in North America. As one of the 10 largest churches in the world, the Basilica features over 80 chapels/oratories as well as extravagant domes with detailed mosaics in the Romanesque-Byzantine architectural style. 

As the national Catholic Church of the United States, the shrine has experienced several papal visits including Pope John Paul II, Pope Benedict XVI and, most recently, Pope Francis in 2015. During his first visit to the United States, Pope Francis visited the Basilica of the National Shrine of the Immaculate Conception to canonize 18th century Spanish Franciscan missionary Saint Junípero Serra, who founded 21 missions in California. The canonization of this “Californian” saint at the church was heavily covered in the media, including the New York Times, the front cover of Newsweek, USA Today and C-SPAN.

The “crowning jewel” of the shrine is the Trinity Dome. It depicts the Holy Trinity, the Virgin Mary and a procession of saints who have an association with the United States and the National Shrine. In celebration of the Basilica’s 100th anniversary, MAPEI provided products to complete the delicate installation of more than 18,300 sq. ft. (1,700 m2) of Venetian glass tile.  

Installation challenge at a height of 159 feet

The Trinity Dome is one of the most visually striking and physically extraordinary mosaics in the world, echoing those from the ancient world. The installation process – which featured MAPEI products – also employed age-old techniques, turning the installers into high-climbing artisans. 

Having previously installed mosaics on three smaller domes within the Basilica, when the crew from Rugo Stone won the bid for the tile installation of the mosaic in the main dome, they immediately began working with the archdiocese, the architects and MAPEI on a plan to install the soaring artwork in the most unobtrusive manner possible. 

Being a sacred place of worship, as well as the National Basilica, the church had to remain open during the installation. Further, nothing could fall from the jobsite. At that height, even the smallest tile could be deadly if dropped. So, an elaborate safety system was devised. The mosaic fabrication and installation processes were completed using a unique scaffolding system anchored into the structure of the Basilica itself. The deck/base of the enclosed compartment was six floors above the central aisle (known as the nave) and featured eight floors of scaffolding rising above the deck in the enclosed compartment to the dome’s apex, where the oculus marks 159 feet (48.5 m) above the nave. The worksite also included an air exchanger and ceiling cover to hide the installation crew from the worshippers below and to avoid interruption of regularly scheduled services. 

MAPEI products on the jobsite

All of the work was completed using MAPEI’s ANSI A118.15E-compliant Kerabond/Keralastic System. An installation of this kind required a tile mortar with a high-performance bond. This two-part system provided exceptional bond strength, flexibility and elongation. A flexible yet strong mortar was imperative, as failure was not an option. The specified mosaic embellishment consisted of 14 million pieces of specialized Venetian glass, totaling 24 short tons (21.8 metric tons) of tile across 18,300 square feet (1,700 m2) of the dome.

First, the Rugo Stone team completely removed all of the old plaster. Then, working in a manner reminiscent of their artistic forebearers in Ravenna, they hand-set the handmade Venetian glass tiles throughout the project. Given the delicate nature of the tiles – and of the setting – through their work, the Rugo crew returned to the classic past.

To complete the complex design of gold and glass tile, installers laid on their backs to individually place each tiny tile. Only a handful of contractors in the United States are capable of completing such a project – especially given the fact that the Trinity Dome project is one of the largest mosaics of its kind in the world – and the tile had to be hand-set. But the crew from Rugo Stone knew the enormity of the task. They had previously completed mosaics in three other smaller domes on the property. And now, thanks to these craftsmen in conjunction with MAPEI, the basilica’s dome is a golden, glittering heaven in celebration of the National Shrine’s 100th anniversary.


The Basilica of the National Shrine of the Immaculate Conception – Washington, D.C., USA

Period of construction: 2015

Period of intervention: 2017

Where MAPEI products were used: MAPEI’s Kerabond/Keralastic System was used to install Venetian glass tile on the ceiling of the Basilica’s Trinity Dome.

Project owner: Roman Catholic Archdiocese of Washington

Charles Donagh Maginnis

Installer: Rugo Stone LLC

MAPEI distributor: Morris Tile

MAPEI coordinators: Gary Waldron, Allen Janofsky,
Vince Linton

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