Nearly 80 years have elapsed since construction began at Meridian Hill Park in Washington, DC. Yet the structural and ornamental exposed aggregate concrete has weathered the decades better than its immediate neighborhood and is in remarkably good condition today.
The work at Meridian Hill probably stands as the first refined large scale use of exposed aggregate concrete for architectural purposes. Architectural sculptor John Earley and his studio were retained to do much of the actual work. The original plan called for reinforced concrete with a stucco finish. The first sample wall, cast in place and then stuccoed, was disappointing in both color and texture. In a second trial, Earley introduced pebble-dash stucco. The improved version still lacked the color that was desired. Then the idea emerged of using the pebbles which were already part of the mix. Forms could be removed while the concrete was still green and surfaces brushed with wire brushes until the aggregate came to light. Earley immediately saw an improvement with this method; he felt that the sense of strength and size were enhanced, and the wall did not seem merely plastered. But most startling of all was the color. As John Earley described it: "The surface which had been wholly gray was broken in spots by clean pebbles in their natural color which varied from white, to yellow, to light brown...
These spots relieved the gray of the cement to such an extent that they imparted to the whole structure a cream color which was a decided step forward and a great improvement." The exposed pebble texture was selected for use on wall panels, rusticated blocks of the retaining wall piers, and for balustrades, urns, and accessories, many of which were precast. Borders around wall panels were tooth chiseled and rusticated grooves on the piers were left untouched.
The worst fault of the new technique was a tendency for pebbles to bunch into pockets surrounded by areas of gray sandy mortar which would give a blotchy appearance to the wall. Earley's attempts to fix the problem resulted in a mix that used only one size of pebbles and one size of sand particles. This grading gave uniformity and also a maximum amount of aggregate surface exposed by brushing. Earley called it step grading; it is more commonly referred to as gap grading today, and it is practiced in various ways for all modern exposed aggregate concrete.