Exposed concrete isn't a finish applied afterwards — it's the one building material whose finish is decided before the pour and can't be corrected afterwards. Every imperfection in the formwork, every air bubble not vibrated out properly, every joint between panels stays imprinted forever in the hardened surface. That's perhaps why, among all building materials, exposed concrete generates the most radically different positions among the architects who turned it into a language: no other material reveals the process that produced it with quite the same honesty.
Tadao Ando: perfection as discipline
Tadao Ando built his entire poetics around an almost obsessively precise exposed concrete. His method — developed as early as the Row House in Sumiyoshi (1976) and refined over dozens of later projects, including the Church of the Light in Ibaraki (1989) — uses treated birch-plywood formwork, with a system of through-holes for the tie rods arranged on a regular modular grid (typically 900 x 1,800 mm, the standard size for Japanese panels) that leaves small, perfectly aligned circular discs visible on the surface. The cement is ordinary grey Portland, but the water-cement ratio is controlled with extreme precision and the vibration is performed by hand, panel by panel, by specialised crews — not an industrialised process but an almost artisanal one, despite the material being the same as on any building site. The result is a surface free of bubbles, uniform, almost polished: concrete as an immaterial material, a surface that absorbs light without reflecting it aggressively.
Peter Zumthor: concrete in dialogue with other materials
Peter Zumthor takes the opposite strategy to Ando: concrete is rarely the sole protagonist. At the Therme Vals (1996), the structural concrete is almost entirely hidden behind slabs of Vals quartzite cut in horizontal courses — but where concrete does appear exposed, in the ceilings and a few technical elements, Zumthor treats it with the same tactile care reserved for stone: formwork chosen to achieve a specific texture, not the absence of texture as in Ando. At the Kolumba Museum in Cologne (2007), Zumthor blends a pigmented light-grey concrete with exposed brick in a single mixed masonry, where the concrete doesn't compete with the brick but completes it chromatically. Zumthor's lesson is that exposed concrete can be a "quiet" material that supports a broader material composition, instead of dominating it.
Kengo Kuma: the reaction against concrete as monument
Kengo Kuma has built much of his critical identity in explicit opposition to the aesthetic of monumental concrete that dominated postwar Japan (the same lineage as Kenzo Tange). In his projects — from the V&A Dundee (2018) to Nagaoka City Hall Aore (2012) — exposed concrete almost always appears in limited portions and always in composition with wood, local stone or slatted screens that fragment its visual perception, reducing the sense of mass. Kuma has spoken explicitly of wanting to "defeat" twentieth-century heavy-concrete architecture with an architecture of light, layered materials — while he keeps using concrete structurally, he treats it as an element to be perceptually masked, not put on display. It's the exact opposite of Ando's position, despite sharing the same country and the same generational reference point.
Eduardo Souto de Moura: concrete as Portuguese stone
Eduardo Souto de Moura, working within the Portuguese architectural tradition that also includes Álvaro Siza, often treats exposed concrete as a contemporary substitute for the traditional granite stone of northern Portugal — a warm colour achieved with local aggregates, surfaces that age and weather over time instead of staying "clean" as in Ando's work. At the Municipal Market of Braga (a conversion of the stadium, 2003) and in numerous single-family houses, Souto de Moura uses rough-timber-board formwork that leaves a rustic, almost vernacular texture — a concrete that declares its regional belonging instead of aspiring to a universal abstraction.
What actually changes in the mix design
Behind every aesthetic choice are precise, controllable technical variables. Colour depends on the type of cement (white CEM I 52.5 R for Ando and for light finishes, ordinary grey with iron-oxide pigments for warm tones as in Souto de Moura's work) and on the type of fine aggregate visible at the surface. Texture depends on the formwork material: steel or plastic-coated panels for smooth, uniform surfaces, rough timber or textured rubber for pronounced material textures. The presence or absence of surface air bubbles depends on the sequence and intensity of vibration — a parameter controlled on site with needle vibrators inserted at regular intervals, never randomly. None of these choices can be corrected after striking the formwork: which is why, on the most ambitious projects, full-scale sample panels are always cast before the final pour, explicitly approved by the project's artistic direction.