Traditional Masonry Archives — Architect's Corner: King Street Station, Seattle, Wash.

Architect's Corner: King Street Station, Seattle, Wash.

Constructed of brick masonry with a steel frame, the building contains a campanile that imitates the design of a station located in the Piazza San Marco in Venice, Italy. Granite and terra cotta define elements of the entire facade, all of which is surrounded by red face brick. The original interior finishes include white marble wall panels bordered by glass tile, terrazzo inlay surrounded by granite mosaic floor tile, and ornamental plaster on ceilings and walls.

In an effort to modernize the station’s interior, inappropriate alterations were completed during the 1950s and 1960s. Unfortunately, this work included demolition of some historic finishes and features. Portions of the interior finishes were hidden from view after remodeling. Among the significant areas of concealed original finish work were the upper half of the main waiting room and the clerestory space of the Compass Room, the entry vestibule located at the base of the clock tower.

As part of several planned phases to restore the station, a limited project, funded by Amtrak and the Washington State Department of Transportation, completed the restoration of the Compass Room and select areas of the building. Otak Inc., the lead architecture firm, hired Wiss, Janney, Elstner Associates Inc. to provide historic preservation consultation and repair services. The expertise of plaster specialists Hayles & Howe Inc. enabled fabrication and restoration of the ornamental plaster.

The rehabilitation

The scope of the restoration of the two-story Compass Room vestibule, so named for the inlaid tile and terrazzo compass in the floor, included repair, replacement and restoration of several historic finish materials. A period of significance was easy to identify due to the treatment of the interior finishes having been essentially unchanged before the modernization and its damaging effects. The Secretary of the Interior’s Standards for Rehabilitation was used as the standard for the restoration project.

At the lower level of the entry vestibule, white marble cladding on the columns, pilasters and soffits was repaired and missing panels were replaced in kind. Similarly, missing bands of inlaid glass tile were replaced on the walls, columns and pilasters. Granite mosaic floor tile was also repaired and replaced. At the upper level of the Compass Room, ornamental plaster elements were restored or replaced. The restoration of each of the historic finishes was relatively straightforward for preservation projects. However, it was the work involved with restoration of the plaster that presented the most challenges.

Much of the original and surviving areas of high-relief plaster were intact. However, the project scope included several conditions requiring repair of the existing materials or fabrication of new plaster. Rehabilitation of the plaster included repair of plaster damaged during the modernization project as well as replication of missing ornamentation and original plaster that was lost to time. The project scope also included addressing the appearance of the plaster, treating nearly 100 years of accumulation of multiple paint applications, surface dirt and deposits, and atmospheric staining.

The removal of modern finishes exposed the masonry backup wall to which the original plaster was anchored. Exploratory investigation confirmed that the original plaster was not applied to lath but was secured to the masonry only with a direct bond of plaster. Careful consideration was given to the rehabilitation process of each component of the plaster assembly, particularly composition of the new plaster mix, attachment methods of new plaster to the masonry, paint removal from and repair of existing plaster, and paint application on both existing and new areas. Most of the repair work included surface applications of new plaster to rebuild or reconstruct damaged plaster.

The process used to fabricate the new plaster differed from the traditional method that was used in
the original construction. Factors that contributed to this decision included the opportunity to create new cartouches in a controlled environment with conventional and contemporary methods successfully used by Hayles & Howe. Plaster replacement pieces were fabricated off-site because the plaster company facilities were located on the other side of the country, in Maryland. Hayles & Howe planned to prefabricate large wall panels containing both ornamental shapes and flat surfaces. Creating prefabricated panels would reduce fieldwork and project costs. The panels would simplify installation of the replacement plaster, and Hayles & Howe assured the architects that the company had successfully completed several similar rehabilitation projects using the same off-site, prefabrication process.

New replacement plaster shapes were created in a two-step process. First, representatives from Hayles & Howe visited the site to determine which pieces would be suitable models for mold creation. Silicone rubber was brushed on and layered over model areas to make the molds. The molds were created of isolated areas of ornament that would be pieced together in the shop to form new cartouches and other shapes. Hayles & Howe also made new castings using the rubber molds.
Before the creation of field molds could be completed, an existing buildup of multiple layers of paint required careful removal. Through mockups and trial coating-removal samples, products and methods were identified that would successfully and carefully remove the existing interior paint and expose the original plaster surfaces. In conjunction with the paint removal, a study of the historic paint colors was completed in order to be able to restore the original appearance of the plaster.
Contemporary attachment methods were used to install the new plaster. New steel shelf angles anchored to the backup masonry supported the large and heavy prefabricated panels at the base of each cartouche. After the panels were set on the angles, counter-sunk Tapcon screws laterally attached the plaster to the masonry. The counter-sunk holes were filled with new plaster. The horizontal legs of the shelf angles were flush or nearly flush with the face of the prefabricated models. After the angles were trimmed, subsequent installation of marble panels below the plaster concealed the bottom leg of the angle.

A paint failure

A problem arose when newly applied interior paint on some of the restored plaster panels began to fail. Parts of coating were blistering, peeling, and exhibiting poor adhesion shortly after application of the primer coat. At these locations, portions of the plaster became moist and fragile. The area of concern was located on the interior side of an exterior masonry wall at the second floor level. The presence of peeling paint and concern about loss of original plaster due to damage delayed the plaster restoration until a cause of the failure was determined.

Representatives from the coating manufacturer measured elevated moisture content in areas of failed primer. The moisture content readings were generally well above the maximum recommended plaster moisture content of 15 percent, ranging from the upper teens to the lower 30s. High moisture content in paintable plaster substrates inhibits the successful adhesion of applied coatings. The investigation revealed that a small roof area on the second-floor level was leaking and allowing water infiltration to the brick masonry substrate behind the plaster. The location of the leakage coincided with the problematic areas of paint failure.

Additional factors contributed to the failure of the primer coat. The primer used did not match those specified for use on plaster and was inappropriate for the conditions. Another contributing factor was inadequate preparation methods performed prior to application of the primer. In an attempt to evaluate preparation effectiveness, adhesion testing was completed using Method A of ASTM D3359-02, Standard Test Methods for Measuring Adhesion by Tape Test. Dust and debris was observed underneath the primer coat on the plaster. It was visible to the naked eye and under magnification. The presence of debris was preventing an adequate bond of the coating.

In order to address the primer coat failure problem, the roof leak was repaired and loose coating was removed. The substrate masonry and the plaster were given time to dry to acceptable moisture content levels for paintable substrates. Concurrently, a new coating system was selected for application. The new coating system was highly alkaline, resistant to efflorescence, and exhibited an adequate bond to the properly prepared painted-plaster substrate. Once the plaster dried to appropriate recommended levels, the coating system was applied.

Periodic reviews of the finished project over the last two years have revealed that the coating failure conditions encountered during the restoration were effectively addressed.

While the main waiting room and other remaining areas of the station await funding for further restoration, the rehabilitated interior finishes testify to the brilliance that the restored materials retain.

Anita Washko and Mark Morden work in the Seattle offices of Wiss, Janney, Elstner Associates Inc.

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