What are Exposed Concrete Classes?
Exposed concrete is one of the defining design elements of modern architecture. Unlike concrete components that are later plastered, clad or coated, exposed concrete remains permanently visible and therefore has a significant impact on the appearance of a building.
The higher the aesthetic expectations for the concrete surface, the more important it becomes to define the required surface quality precisely. For this reason, exposed concrete surfaces are classified into different exposed concrete classes.
An exposed concrete class does not describe the strength or structural performance of the concrete. Instead, it refers exclusively to the visual quality requirements of the finished concrete surface.
For architects, designers, clients and contractors, exposed concrete classes provide a common basis for planning, tendering, mock-ups and quality control.
On this page, you'll find an overview of the exposed concrete classes SB1, SB2, SB3 and SB4, including their quality requirements, assessment criteria and typical applications.
How are Exposed Concrete Classes Defined?
The classification of exposed concrete is based on the German guideline "Exposed Concrete" published jointly by the German Society for Concrete and Construction Technology (DBV) and the Association of German Cement Manufacturers (VDZ).
For many years, this guideline has served as the recognized basis for planning, specifying and evaluating exposed concrete surfaces. It defines four exposed concrete classes SB1 to SB4 and outlines the corresponding visual quality requirements.
Exposed Concrete Class SB1
SB1 describes exposed concrete surfaces with low aesthetic requirements.
Although the concrete surface remains visible, it is not a primary architectural feature. Minor variations in colour, porosity or formwork appearance are acceptable.
Typical applications include:
- Technical structures
- Underground car parks
- Basement areas
- Utility rooms
- Infrastructure projects
Exposed Concrete Class SB2
SB2 represents standard aesthetic requirements and is the most commonly specified exposed concrete class for building construction.
The requirements for surface consistency, pore distribution and formwork appearance are higher than for SB1 while remaining practical and cost-effective to achieve.
Typical applications include:
- Residential buildings
- Office buildings
- Schools
- Commercial buildings
Exposed Concrete Class SB3
SB3 describes exposed concrete surfaces with high aesthetic requirements.
The concrete surface becomes an intentional architectural feature and plays a key role in the building's visual identity. Consequently, higher standards apply to pore distribution, colour consistency, formwork appearance and detailing.
Typical applications include:
- High-quality façades
- University buildings
- Public buildings
- Representative interior spaces
- High-end residential architecture
For many architectural projects, SB3 offers an ideal balance between design quality and construction effort.
Exposed Concrete Class SB4
SB4 represents exposed concrete surfaces with the highest aesthetic requirements.
Here, the concrete surface becomes a central architectural design element. As a result, planning, mock-ups, execution and quality control require the highest level of attention.
Typical applications include:
- Museums
- Cultural buildings
- Corporate headquarters
- Research facilities
- Landmark public buildings
Successfully achieving SB4 quality requires close collaboration between all project participants, beginning as early as the design phase.
Which Criteria are Used to Assess Exposed Concrete?
The quality of an exposed concrete surface is never judged by a single characteristic alone. Instead, the DBV/VDZ guideline evaluates several aspects of the finished surface.
Formwork pattern
The formwork pattern includes the arrangement of panel joints, construction joints and tie holes. These elements have a major influence on the architectural appearance of exposed concrete and should be considered during the design phase.
Surface porosity
The number, size and distribution of air voids significantly affect the visual quality of a concrete surface. Higher exposed concrete classes require increasingly uniform pore distribution.
Colour and colour consistency
Concrete is a natural building material. Nevertheless, especially for higher exposed concrete classes, strict requirements apply regarding colour consistency and overall visual uniformity.
Surface flatness
Surface irregularities can become particularly noticeable on large façade elements. Flatness is therefore an important criterion when assessing exposed concrete quality.
Surface texture and finish
In addition to smooth exposed concrete, textured surfaces can also be produced. Formliners create the desired surface texture and are deliberately used as an architectural design element.
Why are mock-up panels important?
As the aesthetic requirements for exposed concrete increase, mock-up panels become an essential part of the planning and construction process. They provide a physical reference that allows architects, clients, contractors and concrete suppliers to evaluate and agree on the expected surface quality before construction begins.
Particularly for SB3 and SB4 projects, mock-ups help define key visual characteristics such as formwork appearance, joint layout, tie-hole arrangement, colour consistency, porosity and overall workmanship. By establishing a shared quality benchmark at an early stage, they improve communication between all parties, reduce the risk of misunderstandings and costly rework, and provide a reliable standard against which the finished exposed concrete can be assessed.
Comparison of Exposed Concrete Classes
| Criterion | SB1 | SB2 | SB3 | SB4 |
|---|---|---|---|---|
| Design Requirements | Low | Standard | High | Very high |
| Formwork Appearance | Basic | Increased | High | Very high |
| Colour Consistency | Basic | Increased | High | Very high |
| Mock-up Panels | Rarely required | Project-dependent | Recommended | Generally required |
| Typical Projects | Technical structures | Residential buildings | High-quality architecture | Premium architecture |