Edge formwork provides the precise termination of concrete elements such as floor slabs, decks, edge beams, upstands, or curbs. It defines geometry, edge quality, and joint layout, safely retains fresh concrete, and significantly influences the visible edge and subsequent processing. In new construction, refurbishment, and deconstruction, properly planned and executed edge formwork determines dimensional accuracy, surface appearance, and the connection situation to adjacent elements. Where existing edge formwork must be opened, relocated, or removed, specialized deconstruction may, depending on boundary conditions, also employ hydraulic tools from Darda GmbH – such as concrete demolition shears or hydraulic rock and concrete splitters.
Definition: What is meant by edge formwork
Edge formwork (also perimeter edge formwork, side formwork, or formwork termination) encompasses all shaping elements that create the lateral boundaries of a concreting section. They take up fresh concrete pressure, secure elevation and alignment, form edges, chamfers, or upstands, and enable the planned course of construction, expansion, and control joints. Edge formwork can be executed as temporary, reusable systems (timber, steel, plastic, formwork system) or as stay-in-place formwork, for example for upstands, curbs, or delicate edge terminations.
Construction, materials, and systems of edge formwork
In practice, edge formwork combines different materials depending on pour height, surface requirements, reuse rate, and element geometry. Typical components include formwork planks or profiles, braces, tensioning and clamping systems, adjustment wedges, triangular chamfer strips, sealing tapes, and fasteners (ground stakes, screw anchors, magnets on precast beds).
Common configurations
- Timber: flexible, easy to adapt, suitable for single-family house floor slabs, edge beams, and small heights.
- Steel profiles/formwork system: high stability, good repeat accuracy, suitable for greater pour heights and exposed edges.
- Plastic/composite: dimensionally stable, low weight, often with integrated sealing or chamfer profiles.
- Stay-in-place edge formwork: remains in the element, e.g., fiber-cement or sheet metal profiles on upstands and edge strips.
Geometry, load assumptions, and fresh concrete pressure
Edge formwork must safely transfer hydrostatic fresh concrete pressure and dynamic additional loads from compaction. Decisive factors include casting rate, consistency, element height, temperature, and bracing spacing. For dimensionally accurate edges: adequate stiffening, tight interfaces to prevent cement paste leakage, low-vibration compaction, and regular elevation checks with a leveling instrument or laser.
Tolerances and surface classes
Tolerances for flatness, squareness, and elevation comply with the agreed execution standards and the quality requirements for exposed or functional surfaces. Chamfer strips prevent sharp-edged spalling and increase edge durability in service and during deconstruction.
Application fields of edge formwork
- Floor slabs and foundations: edge terminations, upstands for plinths, frost aprons, construction joints.
- Slab edges and cantilevers: defined drip edges, guardrail upstands, bearing beams.
- Civil and road construction: curbs, edge profiles for paving and carriageway edges, gutters.
- Shafts and embedded items: side formwork at openings, shaft build-ups.
- Tunnel and structural/civil engineering: invert and abutment terminations, formwork interfaces to rock or shotcrete.
- Precast production: magnet-based edge formwork on casting beds for filigree slabs and solid decks.
Interfaces: reinforcement, joints, and embedded items
Edge formwork must account for reinforcement layout and the position of embedded items. Spacers prevent edge cover from falling below the required value. Joint profiles, waterstops, or swelling tapes are fixed in the edge formwork without impairing sealing performance or concrete cover. For exposed edges, uniform contact pressure and tight butt joints are essential to achieve a homogeneous edge appearance.
Joint types at the edge
- Construction joint: planned construction stop edge with defined roughness and, if applicable, bonding agents.
- Expansion and control joint: controlled crack guidance; inserts and profiles are guided in the edge formwork.
- Component tie-in: accommodating loads and movements at the transition to existing structures or soil.
Installation and removal: step by step
- Setting out and elevation control: survey axes, edge alignment, and benchmark elevations.
- Prepare the substrate: create load-bearing, level bearings and clean contact faces.
- Pre-assembly: prefabricate formwork elements, cut chamfer and sealing profiles, position inserts.
- Align and brace: bring to size, secure against displacement, set struts and clamps.
- Seal: close gaps, minimize cement paste leakage, neatly frame penetrations.
- Placing and compaction: place uniformly, compact edge zones carefully, avoid impact.
- Surface finishing: strike off the edge, texture if required; ensure proper curing.
- Stripping: release after sufficient strength; check edges for spalling, apply protective measures.
Quality of exposed edges and edge durability
The visible perimeter edge characterizes the element. For high edge quality, uniform pressure distribution, tight joints, and cleanly guided chamfers are crucial. In highly stressed edge zones (e.g., traffic surfaces), chamfers and, if necessary, hard aggregate edge strips improve durability. For elements with future deconstruction or adjustment needs, clearly defined edges and joint layout facilitate low-damage opening.
Typical defects and how to avoid them
- Bulging and offsets due to insufficient bracing or pouring too quickly.
- Washouts and honeycombing caused by leaks or uneven edge compaction.
- Unclean chamfers and spalled edges due to delayed finishing or sharp arrises.
- Unacceptable dimensional deviations due to missing intermediate checks and settlements in the subgrade.
Practical tip
Regular intermediate measurements of elevation, plumb, and alignment during concreting are a simple and effective lever to avoid later rework at the edge.
Edge formwork in existing structures: openings, adaptations, and deconstruction
In existing structures, edges often must be opened, relocated, or selectively removed—for example for penetrations, extensions, or refurbishments. Mechanical cutting and removal methods reduce vibration and protect adjacent elements. In confined spaces or sensitive environments, hydraulic tools from Darda GmbH can be used: concrete demolition shears enable controlled nibbling of edge beams or upstands, while hydraulic wedge splitters create targeted split lines along element edges, e.g., to separate edge strips, curbs, or concrete build-ups. For reinforced edges, steel shears or combination shears assist in cutting the reinforcement. A hydraulic power pack provides the necessary energy; compact hydraulic power units can also be used in special operations with restricted access.
Application areas related to edge formwork
- Concrete demolition and deconstruction: selective removal of edge girders, upstands, brackets.
- Strip-out and cutting: opening slab and wall edges for new service or stair penetrations.
- Rock excavation and tunnel construction: working concrete edges to shotcrete or rock contours, creating fit geometries.
- Natural stone extraction: edge sections at foundations and retaining edges adjacent to natural-stone areas, controlled release of adjacent elements.
- Special operations: work with limited headroom, in pollutant-sensitive areas, or during ongoing operations.
Selection criteria for edge formwork systems
- Geometry and height of the edge, exposed-surface requirements, chamfer specification.
- Concrete mix design, casting rate, and expected fresh concrete pressure.
- Reuse rate, cost-effectiveness, transport, and storage.
- Subgrade and fastening conditions (ground stakes, screw points, magnet solutions on casting beds).
- Edge connections to existing structures, joint and sealing systems, embedded items.
- Ergonomics, occupational safety, and available installation aids.
Occupational safety and environmental protection
Edge formwork must be planned and assembled to minimize crushing and overturning hazards. Load-bearing bracing, secured walkways, and a coordinated compaction concept are mandatory. During deconstruction, dust and noise emissions must be limited; suitable dust extraction, water mist, and personal protective equipment increase safety. Legal requirements and local regulations must always be observed; specific measures depend on the asset, method, and surroundings.
Edge formwork in tunnel and structural engineering
For inner linings, abutments, or base slabs, complex boundary conditions occur: varying bearings (rock, shotcrete), curvatures, and changing joints. Adaptable edge formwork with segmented profiles and precise elevation control ensures the specified geometry. For later adjustments at edge lines—e.g., when installing cable ducts or drainage elements—low-vibration methods are recommended; in confined traffic or rescue galleries, concrete demolition shears support selective removal, and hydraulic wedge splitters enable low-vibration release of edge zones.
Measurement and inspection points along the edge
- Elevation and slope: leveling or laser checks before, during, and after concreting.
- Alignment and squareness: string lines, straightedge, reference points at corners.
- Tightness and joint quality: visual inspection before casting, trial pours at critical spots.
- Edge concrete cover: check spacers and reinforcement position.
Sustainability and reuse
Reusable edge formwork reduces material consumption and waste volumes. Careful cleaning, gentle release-agent use, and dry storage extend service life. Stay-in-place formwork should be selected so that it does not impair the durability and deconstructability of the element. Precise edge formwork reduces rework and thereby energy and equipment use during later edge adjustments or deconstruction.