architectural concrete
Concrete that is exposed to view because it forms part of a surface, and may therefore need special attention given to its appearance.
architectural concrete: concrete that must look good on sight
Architectural concrete is concrete left exposed to view as a finished surface, rather than hidden behind cladding, plaster, or paint. It carries the structural load while also serving as the visible aesthetic finish. This dual purpose means it must meet both performance and appearance standards that standard concrete does not.
The concrete mix itself differs from structural concrete in several ways. Designers typically specify lower water-cement ratios, often 0.40 to 0.45, to reduce surface porosity and colour variation. Aggregates are carefully selected for size, shape, and colour consistency; many projects call for single-size coarse aggregates or washed gravel to create uniform texture. Admixtures such as plasticisers and air entrainment agents are common. Some mixes include white cement instead of grey Portland cement as the binder, or incorporate pigments for intentional colour.
Formwork becomes critical. Board-marked concrete is achieved with plywood or timber shuttering that leaves a visible wood grain or board-joint pattern. Bush-hammered finishes break the surface with a pneumatic tool to expose aggregate beneath, creating texture and hiding minor surface flaws. Fair-faced concrete relies on smooth plywood forms and meticulous casting technique to achieve a smooth, uniform appearance with minimal voids or honeycombing. Some work specifies acid-etched finishes applied after curing to expose aggregate further.
Defects in architectural concrete are costly and permanent. Honeycombing (exposed aggregate pockets), blowholes, form lines, colour streaking, and efflorescence (white salt deposits) all remain visible on the final structure. Surface crazing from rapid drying is largely cosmetic but indicates poor curing control. Concrete cancer, caused by steel reinforcement corrosion, stains the surface and demands urgent repair. Careful attention to pour sequencing, vibration, ambient temperature, and curing duration (typically 7 to 28 days of damp conditions) is essential.
Architectural concrete dominates Brutalist and contemporary design; it is found in office buildings, civic structures, universities, and residential towers where the material itself is the aesthetic statement. It is demanding to produce and expensive to remedy, making site supervision and quality control non-negotiable. Concrete finishes must be agreed and sampled before work begins; colour and texture panels are standard practice to set expectations.