Exposed concrete is far more than just a utilitarian building material: it is a surface, a structure, and a design element all at once. The production of exposed concrete combines sophisticated construction chemistry with precision craftsmanship and design excellence, because every visible concrete surface is the direct result of all the decisions made jointly by planners, formwork builders, and concrete contractors. Those who truly understand exposed concrete recognize in every pore, every joint, and every texture the sum of the mix design, placement technique, and curing.

• What defines exposed concrete and how it differs from structural concrete
• Which raw materials and concrete mix designs have a decisive influence on the surface
• How formwork, release agents, and compaction determine the quality of the exposed concrete surface
• Which exposed concrete classes are distinguished according to the DBV technical bulletin and what they mean
• How curing, protection, and surface finishing ensure durability
• What typical defects occur during the production of exposed concrete and how to avoid them
• Where exposed concrete is used in building construction, civil engineering, and interior finishing
• What design possibilities and limitations the material offers

What Is Exposed Concrete? Definition, Distinction, and Classification

Exposed concrete refers to concrete surfaces that remain permanently visible after formwork removal and must therefore meet both design and aesthetic requirements. The term is distinguished from concealed structural concrete, which is subsequently plastered, clad, or otherwise finished. With exposed concrete, the surface is the final product: it must be uniform, flawless, and visually appealing, without the possibility of subsequent layers concealing defects. This characteristic makes the production of exposed concrete one of the most demanding disciplines in concrete construction.

The distinction is not merely aesthetic. Exposed concrete is subject to heightened requirements regarding homogeneity, color consistency, texture, and pore distribution. At the same time, it must meet all structural and durability requirements placed on concrete as a load-bearing material. The “Exposed Concrete” technical bulletin published by the German Concrete and Construction Technology Association (DBV) is the authoritative set of standards in German-speaking countries and defines four exposed concrete classes (SB1 through SB4), ranging from basic requirements to the highest quality levels. This classification serves as both a basis for planning and a tool for drafting specifications.

Historically, the deliberate use of exposed concrete surfaces dates back to classical modernism. Le Corbusier coined the term “béton brut” (raw concrete), which defined an entire architectural movement—Brutalism—in which the untreated concrete surface became a programmatic expression of material honesty. Buildings such as the Unité d’Habitation in Marseille or the Parliament Building in Chandigarh demonstrate that exposed concrete functions as a means of design expression far beyond its structural purpose. This tradition continues in contemporary architecture, from Tadao Ando’s meditatively smooth concrete shells to the rough-textured facades of the contemporary Brutalism revival.

Raw Materials and Concrete Mix Design: The Foundation of Exposed Concrete Production

The quality of an exposed concrete surface does not begin at the formwork, but in the mix design. Cement, aggregates, water, admixtures, and additives together form the concrete mix, and each of these components leaves its mark on the finished surface. For the production of exposed concrete, therefore, careful coordination of all components is essential—far beyond what would be required for concealed concrete.

Cement plays a decisive role in determining the color and brightness of the surface. Portland cement (CEM I) typically produces a light gray to gray-beige surface. White cement, which is clinkerized from raw materials with particularly low iron content, allows for significantly lighter or colored surfaces. Cements containing granulated blast furnace slag (CEM III) tend to have a blue-gray tint that lightens over time due to carbonation. To ensure uniform color, it is crucial to use the same cement from the same production facility throughout the entire construction project, as even cements of the same nominal grade from different plants can produce color variations.

The aggregate influences the surface and structure in several ways. Fine sands determine the texture of the zone near the formwork; coarse aggregates characterize the fracture pattern in bush-hammered or sandblasted surfaces. For exposed concrete, washed, color-sorted sands and gravels are often used to achieve the most uniform appearance possible. Here, too, it is important to avoid changing suppliers during construction, as color differences in the aggregate will be directly visible on the surface. The water-to-cement ratio (w/c ratio)—that is, the ratio of water to cement in fresh concrete—has a direct influence on porosity and strength: A low w/c ratio results in a denser, stronger, and more durable surface, but makes the concrete more difficult to work with. Superplasticizers, as concrete admixtures, make it possible to combine a low w/c ratio with sufficient workability.

Pigments can be mixed directly into the concrete to create colored exposed concrete surfaces. Iron oxide pigments are the most commonly used inorganic colorants because they are lightfast, alkali-resistant, and durable. The dosage must be precisely reproducible, which is why particularly strict batch documentation is required for exposed concrete with color additives. Even slight variations in pigment dosage result in visible color differences between individual concrete pours.

Formwork, Release Agents, and Compaction: Craftsmanship on the Surface

Formwork is the crucial shaping tool in the production of exposed concrete. It determines the texture, pore pattern, joint spacing, and surface character of the finished component. Smooth formwork made of coated plywood (film formwork), steel, or plastic produces a nearly pore-free, mirror-like surface. Untreated wooden formwork transfers the grain and texture of the wood to the concrete, creating a lively, textile-like appearance. Textured matrices made of foam or rubber allow for the transfer of complex relief patterns. The choice of formwork is therefore a fundamental design decision that must be made as early as the design phase.

Release agents are applied to the formwork surface to facilitate demolding and protect the surface. For exposed concrete, film-forming release agents based on mineral oil, vegetable oil, or wax are commonly used. The choice of release agent significantly influences the pore pattern: Too much release agent leads to voids (hollows directly beneath the formwork surface), while too little increases the risk of adhesion and spalling during demolding. The even, thin application of the release agent is a skilled task that requires experienced personnel. Reactive release agents—so-called fatty acid-based form release agents—react chemically with the cement paste to form a soapy film that enables particularly uniform surfaces.

The compaction of fresh concrete is of paramount importance for the quality of exposed concrete. Insufficiently compacted concrete contains air pockets that become visible on the surface as pores or voids. Internal vibrators (immersion vibrators) are the standard tool; they must be used at regular intervals without touching the formwork, as contact leaves indentations and causes color changes. For thin components or areas where an internal vibrator cannot be inserted, external vibrators or vibrating formwork are used. Self-compacting concrete (SCC) offers an interesting alternative: It flows into the formwork under its own weight and compacts without mechanical action, which enables particularly uniform surfaces but requires very precise control of the mix design.

Concreting Speed and Fresh Concrete Pressure

The concrete placement rate—that is, the rate at which fresh concrete is placed into the formwork—affects the fresh concrete pressure on the formwork structure. High fresh concrete pressure can lead to formwork deformation, which manifests as bulges or joint misalignments on the exposed concrete surface. For high-quality exposed concrete elements, a controlled, uniform placement rate is therefore specified to keep the fresh concrete pressure within predictable limits. At the same time, the placement must not be too slow, as this can result in cold joints: layer boundaries where the concrete that is already beginning to set fails to bond completely with a new layer, appearing as horizontal lines on the surface.

Exposed Concrete Classes According to the DBV Technical Bulletin: Planning, Bidding, and Quality Assurance

The DBV’s Exposed Concrete Technical Guide structures the requirements for exposed concrete surfaces into four classes, ranging from SB1 (minimal requirements) to SB4 (highest requirements). This classification is not a decorative framework but a binding planning and construction tool. It defines requirements for porosity, texture, color, flatness, and formwork class, thereby establishing a common language among planners, those preparing bids, and contractors.

SB1 refers to surfaces with simple requirements, such as those acceptable for retaining walls, basement ceilings, or basement components not accessible to the public. Individual pores, color variations, and slight textural irregularities are permissible. SB2 corresponds to the standard for normal exposed concrete surfaces in building construction, where a uniform texture and consistent color tone are expected, without individual pores or slight color variations being considered defects. SB3 and SB4 describe surfaces with high to the highest requirements, such as those demanded for prestigious facades, museum buildings, religious architecture, or interior surfaces. Here, color consistency, freedom from pores, and flatness are at a level that requires considerable additional effort in terms of materials, formwork, and execution.

For each exposed concrete class, the DBV technical bulletin also specifies the formwork skin class—that is, the requirements for the formwork surface. Formwork skin class 1 permits simple wooden formwork with visible grain; formwork skin class 4 requires high-quality film formwork or steel formwork with a defined surface finish. The combination of exposed concrete class and formwork skin class forms the basis for the bid specifications and acceptance. Without these specifications, there is no basis for a proper assessment of defects, which often leads to disputes in practice.

Reference surfaces are another important tool for quality assurance in the production of exposed concrete. Before the actual concrete pouring begins, a reference surface is created on a less exposed component or on a separately produced sample element to document the desired appearance. This surface serves as a benchmark for all subsequent inspections. Deviations are not assessed according to absolute standards, but rather in comparison to the agreed-upon reference.

Curing, Surface Treatment, and Protection

Curing of freshly stripped concrete is crucial for the durability of the exposed concrete surface. Concrete must be kept sufficiently moist after stripping so that cement hydration can proceed fully. Drying out too quickly leads to shrinkage cracks, loss of strength, and a porous, less durable surface. Curing methods include covering with damp mats, spraying curing compounds, or wrapping in plastic sheeting. The duration of curing depends on the type of cement, temperature, and humidity conditions; DIN EN 13670 specifies minimum requirements.

After curing, the surface can be further processed depending on the design intent. Troweling refers to the mechanical roughening of the surface with a trowel or troweling machine, which exposes the aggregate and creates a vividly textured, stone-like surface. Sandblasting or shot blasting removes the cement skin and also exposes the aggregate, but produces a more uniform, finer texture than bush hammering. Grinding and polishing result in a smooth, almost marble-like surface in which the cross-sections of the aggregate are visible. Acid etching with diluted hydrochloric acid selectively dissolves the cement paste on the surface and exposes the aggregate; this process requires special safety precautions and thorough rinsing.

Water-repellent treatments and impregnations protect the finished exposed concrete surface from moisture penetration, soiling, and chemical attack. Silanes and siloxanes penetrate the concrete and make it water-repellent without altering its appearance. Sealants based on epoxy resins or polyurethanes form a closed top layer that repels stains and dirt but may alter the character of the surface. For exterior surfaces, vapor-permeable hydrophobic treatments are preferable so that moisture that has penetrated the concrete can escape. The choice of the right protection system depends on the exposure, the intended use, and the desired appearance, and should be determined during the planning phase.

Typical Errors and Defects in Exposed Concrete Production

Despite careful planning, characteristic defects repeatedly occur during the production of exposed concrete that impair its appearance or compromise its durability. Cold joints form when fresh concrete is placed on top of concrete layers that have already begun to set, preventing a complete bond from forming. They appear as horizontal lines on the surface and are problematic both structurally and visually. Preventing them requires seamless coordination of the concrete placement work and an adequate placement rate.

Voids and aggregate pockets are cavities or areas within the concrete where the aggregate is not sufficiently bonded to the cement paste; they occur when fresh concrete is not fully compacted or when aggregates segregate. Segregation occurs when concrete is placed from too great a height, is vibrated too vigorously, or has too high a water-to-cement ratio. Voids directly behind the formwork surface are visible as pores; larger aggregate pockets must be repaired, which is particularly difficult with exposed concrete because repairs almost always remain visible as foreign spots.

Color differences between concrete pour sections are a common problem that can have various causes: changes in cement or aggregate size, different w/c ratios, variations in curing duration, or differences in formwork absorption. New formwork panels absorb water differently than used ones, resulting in lighter-colored streaks at the panel joints. Pre-wetting new formwork panels or using formwork that has been uniformly pre-aged can mitigate this effect. Formwork imprints occur when formwork panels have joints, screw heads, or repair areas that are transferred to the concrete surface.

Shrinkage cracks are caused by the concrete shrinking as it hardens and dries. They are particularly undesirable in exposed concrete because they permanently impair its appearance and provide entry points for water and contaminants. Structural measures such as expansion joints, reinforcement, and a carefully formulated concrete mix with low shrinkage reduce the risk of cracking. Sufficiently long curing is also crucial, as drying too quickly promotes early shrinkage.

Applications: Where Exposed Concrete Is Used

Exposed concrete is used in nearly all areas of construction, from infrastructure to interior finishing. In civil engineering, bridges, tunnels, retaining walls, and dams are classic exposed concrete structures in which the surface primarily serves a protective function but is also recognized for its aesthetic value. Bridge piers and abutments are often constructed to SB2 or SB3 standards to ensure a neat, uniform appearance.

In building construction, exposed concrete has become an indispensable element of contemporary architecture. Facades made of exposed concrete define the appearance of museums, administrative buildings, residential buildings, and religious structures. Tadao Ando’s Church of Light in Osaka, Peter Zumthor’s Vals Thermal Baths, and Mies van der Rohe’s New National Gallery in Berlin are examples where exposed concrete is an integral part of the architectural essence. In residential construction, exposed concrete ceilings, walls, and floors are used as design elements in interior spaces, combining raw simplicity with elegance.

In interior design, exposed concrete is gaining importance as a flooring material, wall cladding, and furniture surface. In addition to in-situ concrete, precast concrete elements and cast stone are also used here; these are manufactured under controlled conditions in a factory and thus achieve greater uniformity than in-situ concrete. Precast concrete elements also allow for quality control prior to installation, which is a significant advantage when meeting the highest standards (SB4). Thin-layer concrete screeds and microcement coatings are, strictly speaking, not exposed concrete in the classical sense, but are frequently used in interior design as a substitute for exposed concrete when the weight or structural depth of a genuine concrete component is not feasible.

Exposed Concrete as a Design Material: Possibilities and Limitations

The design range of exposed concrete is broader than the cliché of gray rawness would suggest. By selecting the right cement, aggregate size, pigments, formwork, and surface treatment, finishes ranging from high-gloss white to deep-black basalt relief can be achieved. Textured formwork featuring wood grain, geometric patterns, or organic shapes precisely transfers its texture to the concrete, enabling a level of plasticity that is virtually unattainable with other materials. Exposed concrete can appear warm or cold, rough or smooth, monumental or delicate, depending on the mix design, lighting, and context.

At the same time, exposed concrete has limitations that must be honestly acknowledged. It is difficult to correct: once poured, it can hardly be altered without leaving visible traces. Repairs almost always remain noticeable because fresh concrete ages differently than the surrounding structure. Exposed concrete changes over time: carbonation lightens the surface, weathering creates a patina, and algae and moss colonize porous areas. This aging can be perceived as natural dignity or as neglect, depending on maintenance and expectations. Regular cleaning and periodic water-repellent treatment are necessary to preserve the original appearance.

Another consideration is thermal insulation. Unreinforced or lightly reinforced exposed concrete walls without additional insulation generally do not meet the requirements of the Building Energy Act. Exposed concrete used as a facade material therefore requires either a composite construction with insulation behind it or a curtain wall in which the exposed concrete elements function as a cladding shell. These structural requirements increase the planning effort and costs, but are unavoidable if exposed concrete and energy efficiency are to be combined.

Exposed Concrete Production in the Context of Sustainable Construction

The discussion surrounding sustainability in the construction industry affects exposed concrete on several levels. Concrete as a material is associated with a significant carbon footprint, which stems primarily from cement clinker production. This applies particularly to exposed concrete, as high-quality exposed concrete mixes often contain higher cement content than standard structural concrete. At the same time, exposed concrete offers an advantage over facade materials that require regular replacement due to its durability and low-maintenance nature. Well-executed exposed concrete can last for decades without significant repairs, which improves its life-cycle assessment.

Cement substitutes such as granulated blast furnace slag, fly ash, and silica fume can reduce the clinker content in concrete and thus lower CO₂ emissions. These substitutions are possible for exposed concrete but require careful adjustment of the mix design, as granulated blast furnace slag alters the color and fly ash affects workability. Recycled aggregates from demolished concrete can also be used, but they alter the color and texture of the surface and are only suitable to a limited extent for the highest exposed concrete classes. Research into sustainable exposed concrete mixes is an active field in which materials science and design requirements come together productively.

Conclusion: Exposed concrete as a synthesis of technology and design

Exposed concrete production is not a routine task, but a process that requires a continuous quality chain—from mix design and formwork planning to curing. Every decision made at any link in this chain affects the final product, and the final product remains permanently visible. This characteristic makes exposed concrete one of the most honest building materials of all: it hides nothing; it reveals everything.

Classification according to the DBV technical bulletin, the selection of formwork skin class, the definition of reference surfaces, and precise specifications are not bureaucratic formalities, but practical tools that help planners, contractors, and building owners define shared expectations and avoid disappointments. Anyone planning to use exposed concrete must know and apply these tools.

From a design perspective, exposed concrete remains one of the most versatile and expressive materials in architecture. Its ability to modulate light, reveal texture, and develop its own patina over time makes it a material with depth that extends far beyond its structural function. Those who master the technical fundamentals of exposed concrete production are well-positioned to fully realize this potential—not in spite of the precision the material demands, but precisely because of it.