The Importance of Evaluating and Maintaining Stained Glass Windows – Part 2
By: Jimmy Monahan
Last month’s newsletter article focused on addressing stained-glass windows as a part of building envelope surveys and inspections. Here we will outline what is involved in stained-glass window restoration.
The first step is to have several stained-glass window specialists visit the site and provide proposals to restore the windows. Since there are far fewer stained-glass window specialists than facade contractors and window installers, this is not as simple as it sounds. Stained-glass window restoration is a unique blend of artistry and fine craftsmanship, so it’s imperative that specialists are thoroughly vetted. They should be affiliated with the Stained-Glass Window Association of America and should provide references. The stained-glass specialists should detail their means and methods – explaining and clarifying their schedules, plans for installing temporary protection, estimates for how long windows will be out of service, and any reinstallation delays they foresee. How a specialist will be accessing the windows must also be considered. Do they have their own equipment to access both the interior and exterior of the building? Will they be accessing the windows from supported scaffolding that’s currently in place for a facade project in progress? If so, who will be coordinating access with the specialist and the façade contractor? Having this information leads to the most accurate cost estimates and minimizes the issues that arise during the course of the project.
Once the stained-glass window specialist has been retained, the restoration project must be scheduled, and access provided. Typically, a two to four-person crew will remove the stained-glass windows by accessing them from both the interior and exterior of the building. Mechanical grinders and other hand tools will be utilized to remove the sealant between the lead joints and perimeter trim and the individual glass pieces from the perimeter window trim.
Once the stained-glass is removed, the window specialist will mark the window and location to ensure it goes back to its original location after it’s restored. The glass is transported to the contractor’s shop where craftsmen place tracing paper over the stained-glass and stencil the window pattern and sections. This tracing will be the guide to put the puzzle back together.
Existing pieces of stained-glass are then soaked in water for at least 48 hours to loosen residual lead, putty, and other debris so that it’s easier to remove lead joints from the stained-glass pieces. Additional hand cleaning with a wet cloth or use of a razor blade may be necessary to remove putty or lead from the edges of the glass.
After the glass is cleaned and dried, craftsmen will start at the corner of the window stencil and work their way outward piece-by-piece, joint-by-joint. In order to piece the windows back together, all of the cleaned stained-glass pieces must be placed onto the original stencil. This helps to identify where each piece belongs and provides the profile of the lead joints to be replicated. New lead joints are shaped by placing the glass piece into the joint and pressing along the edge by hand or with a glazing knife. Once the lead joint has been formed, the craftsman uses scissors to cut the lead joints to size.
Wood blocks and nails are used to secure the outer edges of the window frame so that the glass pieces can be tapped into place for a snug fit. In order to fit each glass piece into its corresponding lead joint, a glazing knife is used to shape the flanges of the joints to accommodate the insertion of the glass. Once a piece is set into place, the craftsman presses the knife over the edges of the lead flange to secure the stained glass; sometimes a small hammer and wood block will be used for this task. The craftsman will place a wood block over the joint and tap the block to reshape the lead joint flange to the stained glass. Nails are also utilized to temporarily secure the stained-glass pieces and joints in place while working outward.
Once the newly leaded stained-glass is assembled, oil is brushed onto the ends of the lead joints wherever they intersect. The oil acts as a catalyst for fusing the joints together during the soldering process. Again, starting at a corner and working outward, craftsmen solder the lead joints together piece-by-piece. This involves pressing an iron over an additional piece of lead placed between the ends of the lead joints. The soldering iron melts the lead into a liquid form that is painted over the joints. The soldering process fuses the ends of the lead joints together, from top to bottom, until all of the stained-glass pieces are secured in place. This process requires great adeptness since both the melting and cooling of the lead occur within seconds of its application.
After the new lead joints are soldered and the glass is secured, the contractor will begin the dry-fitting process. A brush is used to apply cement putty between the lead joints and the stained-glass. Then, a series of tools are used to insert and compact the putty into the lead joints, creating a waterproofing system. After the putty has been applied to all of the lead joints, fine tools are utilized to remove latent or excess putty that cannot fit into the joints. The stained-glass and lead joints are then cleaned with a brush.
Next, reinforcement is installed on the stained-glass to provide structural stability. Usually, the new reinforcement will be installed in the same locations as the original reinforcement. In some cases, however, the stained-glass window specialist will opt to install additional reinforcement. If applicable, the next step is to reassemble the reinforced stained-glass windows into their new or refurbished frames. Stained-glass windows can be set directly into stone or other building materials, or into frames that are set into the façade.
The final step before the restored stained-glass is transported to the jobsite is the installation of protective glass over the stained-glass windows. This limits exposure to the elements and reduces wind related stress on the stained-glass pieces. While not required, this highly recommended step will increase the lifespan of the stained-glass. In some cases, the protective glass can be secured to the frames of the windows. If there is enough room in the opening of the façade, it might be possible to secure the protection glass directly in front of the stained-glass. The stained-glass window specialist and building envelope design professional should be consulted to confirm the feasibility of using protection glass.
The process of installing the glass back into its original locations will once again require interior and exterior building access. Once the stained-glass is set into place, sealant will be installed at the perimeters of the interior and exterior window faces. This seals the perimeters and mitigates moisture infiltration. The owner and/or the building envelope consultant should review and approve the sealant product and color prior to installation.
As outlined above, the stained-glass window restoration process is highly complex. A tremendous amount of time, patience, artistry, and mechanics are required to successfully remove, clean, re-lead, waterproof, and reinstall stained-glass windows. A good stained-glass window specialist with the right skill set will not only help mitigate water infiltration into your building but will restore its unique aesthetic. Having an engineer, architect, or other design professional overseeing, monitoring, inspecting, and reporting on all aspects of this restoration project is also very prudent.