1924. Wings were added in 1962, 1965 and 1968. All the windows in the building were the original Hope’s Steel casements. On the original section of the building, which faces the National Mall, the existing windows were stripped and repainted with a TNEMEC high-performance coating, weather strip- ping was added, and original hardware was reconditioned. To improve energy perfor- mance, 3M’s Prestige-series glazing fi lm was installed on the interior face of the single clear glazing to reduce solar heat gain. On the later additions, Quinn Evans
Architects specifi ed Hope Steel’s Landmark Series replacement windows, which closely matched the original Hope’s Steel James-
now
The Eastern Market’s cornice was restored with zinc-tin-coated stainless steel. The same material was used for the decorative chimneys and acroteria elements on the roof that were restored based on historic photos.
town Series profi les and sightlines while adding thermally broken windows with insu- lated glass units. This overall approach was approved by the local reviewing agencies. Masonry repairs are another area where
architects often rely on specifi c products that are compatible with historic masonry. At the National Academy of Sciences, the Dover marble used on the 1924 section of the building is no longer quarried, so Dutchman patching, in which small areas of deterioration are replaced with new, carefully shaped masonry to precisely fi t the removed masonry, with the same stone was not an option to achieve an acceptable match aesthetically. For this reason, the
Jahn system, distributed by Cathedral Stone Products, was specifi ed. Areas requiring a patch repair were fi lled using Jahn M120 repair mortar, a vapor-permeable mortar that is compatible with marble. Prior to in- stallation, the subcontractor color-matched the mortar to be identical to the weathered appearance of the adjacent stone. Larger cracks in the masonry were grouted with Jahn M40 repair grout using injection ports. The cracks then were fi lled at the surface with the repair mortar.