Restoring the Royal Heritage
Article reprinted with permission from Stone World magazine

Renovation & Restoration

Restoring the royal heritage

by Jennifer L. Sanicki

While the preservation and longevity of a historical landmark allows new generations to experience its beauty, the Windsor Castle almost lost out on that chance. In November of 1992, a fire broke out at the castle, causing sections of the tower to fracture, with a possibility of collapsing.

With the decision to repair the damage, the architects at Donald Install Associates of London, England, sought to make the castle every bit as functional as it was in the past. "The overall design goal was the preservation of this medieval castle for continued use, not just as a museum, but for State functions, as a family home and for royal household attendant usage," said Alan Frost of Donald Install Associates.

The make-up of Windsor Castle embodies various types of stones, according to Frost. The general framework consists of Bagshot Heath, recycled Bagshot Heath and Kentish Rag stone. To repair the charred rubble, a variety of preservation techniques were initiated.

At the castle's Brunswick Tower, where completely rebuilding the structure was an undesirable option, crews employed a detailed anchoring system. Through the use of the CINTEC  anchor system, a design was implemented that restored the structure of the tower without disrupting the unstable stonework.

First, diamond drilling techniques created a system of holes within the stone at the tower. A hollow stainless steel section was then inserted into the holes on either side of the cavity. Then, grout was inserted under pressure in order to inflate the surrounding sock throughout. Milk grout passes through the expanded sock to provide a chemical and mechanical bond to all of the materials. According to CINTEC, the installed anchors create a reinforced ring within the stonework to retain the original look of the tower.

The anchors were arranged as a "corset" around the Brunswick Tower.

An ultrasound device -- which is non-destructive to the stone -- checked for deep cracks in stone caused by the peat heat of the fire as well as thermal expansion. Using a "Balvac" system by Balfour-Beatty, consolidation of shattered internal faces of stone were done using vacuum resin impregnation. Salts were removed from water-saturated stone by lime-poultice, which also protected the framework from damage while the stone was drying. Reconstruction was done to badly damaged or structurally dangerous areas using new matching stone as well as strengthening of fire-damaged vaulting. "We had used nearly all of these techniques before and employed them for their appropriateness to the differing requirements, always conserving historic material as undisturbed as possible," Frost said.

Various types of new Bath stone -- chosen to match existing stone -- were used for the ashlar work. "We used Stoke Ground Bath stone for the new ashlar," said Frost. Reigate, chalk and Portland stone were also implemented into the castle's design.

"Achievement [of the design goal] needed considerable skill, both in craftsmanship and in negotiating to satisfy client requirements -- the Royal Household -- and current conservation opinion -- through English Heritage," said Frost. According to Frost, the firm's experience as a conservation architectural practice in the U.K. helped in the success of the project. "The work the firm does involves very old structures that are often in current use," he said.

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