ForMatter/Finishes/stone_finish/Exposed-aggregate concrete
finish_concrete_exposed_aggregate

Exposed-aggregate concrete

stone_finish · textured · exposed aggregate, EA finish, river-stone finish, pebble-paving

The cement paste at the surface of concrete is washed or sandblasted away while still young, exposing the decorative aggregate (river rock, crushed granite, glass cullet) underneath. Reads as a constellation of stones held in a matrix — the architectural surface, more deliberate than broom or salt finish. Mid-century apartment-building exteriors, modern hardscape, museum plazas.

Two methods: (1) Surface retarder — chemical that delays cement set on the top 2–5 mm — applied to the slab immediately after final float; the next day, surface is pressure-washed exposing the aggregate. (2) Sandblast or grind a cured slab to a controlled depth (3–10 mm). Aggregate selection drives the visual: rounded river rock for soft register, crushed granite for sharp / contemporary, recycled glass for color punch. Slip-resistance R-11 to R-13. Cost meaningfully higher than broom-finish; doubles or triples the slab budget when the aggregate is decorative-grade.

character — stone-constellation matrix, architectural-deliberate register, slip-resistant.

Finish properties

  • leveltextured
  • subcategoryconcrete cement-paste removal
  • Ra (µm)5000.0
  • applies tostone
Pairs with materials

Second life

reversibilityzero on the existing stone — texture is geometric, present in the substrate. Re-finishing requires removing material to reach a different finish.
blocks substrate recyclingno
renewabilitymoderate — most stone finishes can be re-applied (re-honing, re-flaming) at the cost of minor material loss; field-renewability for indoor surfaces, shop-renewability for outdoor.

Marble Institute of America / Natural Stone Institute care-and-finish guides; ASTM C1242 dimension stone terminology.

Citations

  • url · https://en.wikipedia.org/wiki/Concrete
  • standard · ACI 303R — Guide to Cast-in-Place Architectural Concrete Practice.
  • book · Forty, *Concrete and Culture: A Material History* (Reaktion Books, 2012).