6 RESTORATION RECOMMENDATIONS

Restoration of the concrete at Meridian Hill Park should proceed according to the general guidelines of quality concrete repair work, with special attention to repair of the exposed aggregate finishes. The exposed aggregate finishes are distinctive for each period of experimentation and embody the various stages in the development of the concrete work within the park. Modern repair materials for concrete, such as polymer modified concrete or integrally mixed bonding agents, are not suitable for the repair of historic concrete. The aggregate for the repair should match the original aggregate of quartz and chert in size, shape, and color. Repair of cast edges and copings must be achieved with formwork rather than through troweling and shaping. Repairing elements from different periods of construction requires skill to match the distinctive finishes achieved. Further, the variety of finishes that were created, often within one integrally cast panel, necessitates matching fine, medium, and coarse gradations of aggregate within the same wall unit. While aggregate may be hand-placed in the concrete repair to match the desired finish, the aggregate must then be covered with the cement repair mix and revealed with a nylon brush after the initial set of the cement to achieve the proper exposed aggregate appearance. Highly exposed, step-graded aggregate should be treated with a cement grout to fill the interstices with cement; the cement is later removed with a nylon brush to expose the aggregate. The restoration of the concrete work should proceed with an understanding of the structural and material properties of the concrete, as well as its importance as a document of construction history.