Formwork Plank for Cast-in-Place Concrete

Formwork planks are among the classic components of concrete formwork. They serve as load-bearing and bracing elements, as supports for formwork panels, or as infill in conventional timber formwork. They therefore directly influence the quality of the concrete surface, the dimensional accuracy, and the safety of the entire formwork assembly. In deconstruction and refurbishment projects where existing concrete is selectively removed, knowledge of the configuration and behavior of formwork planks plays a role in processing anchor points, joint areas, or subsequent openings in an orderly, low‑vibration manner—e.g., with selective concrete crushers for deconstruction or stone and concrete splitters from Darda GmbH.

Definition: What is meant by formwork plank

A formwork plank is a plank made of wood or wood-based material that is used as part of a formwork for producing cast-in-place concrete. Typical variants include solid wood planks (e.g., softwood), 3‑ply formwork panels, glued laminated timber or Kerto beams, as well as specialized plank profiles. Formwork planks perform functions such as load transfer, bracing, spacing, and supporting formwork panels; they can act as planar elements (as sheathing) or line elements (as stringers, chords, walers). Characteristic is their temporary use until concreting and stripping; in special cases they are used as permanent formwork.

Construction, materials, and dimensions

Formwork planks consist predominantly of wood-based materials with defined strength and moisture values. For solid wood, sawing class, oven-dry density, and wood moisture are decisive; for 3‑ply panels, bonding quality (e.g., BFU 100) and face layer thickness. Important for practice:

Typical thicknesses: approx. 19–27 mm (sheathing) up to 40–60 mm (planks, stringers).
Widths: 100–300 mm, depending on system and structural function.
Lengths: adapted to formwork strategy and spans, often 2–5 m.
Surfaces: rough-sawn for high friction, smooth for improved architectural concrete quality.
Edges: chamfered to prevent tear-out; joints often combined with sealing tape for joint sealing.

The choice of material affects the open time until stripping, the surface quality (imprint of joints, grain), and durability over multiple reuse cycles. Planks with high dimensional stability facilitate reproducible results for architectural concrete; robust stringer cross-sections reduce deformations in compression and tension zones.

Function in the formwork system: loads, joints, and anchors

Formwork planks transfer fresh concrete pressure, self-weight, and construction-stage loads into posts, bents, and shoring frames. They define the position of the form face, the joint, and the anchor axes. Key aspects:

Load transfer and deformation

The allowable deflection of a formwork plank determines the final geometry of the component. Undersized planks lead to bulging, blistering, or joint widening. Careful design of stringer spacing and the correct plank thickness minimizes deviations.

Surface quality and joint pattern

Joints between planks appear in the concrete as fine lines. For high-quality surfaces, butt joints are staggered or sealed, contact faces are cleaned and evenly oiled. With board formwork, the wood grain is a design element; with panel or plastic formwork the focus is on homogeneity.

Anchor points, spacers, and tightness

Formwork planks absorb anchor forces via cross-holes, anchor strips, or stringers. The location of the stressing points is relevant for later deconstruction: anchor cones, anchor tubes, and grouted areas can be exposed in a targeted manner when creating openings or refurbishing surfaces. Here, concrete crushers are often used to remove surrounding concrete in a controlled manner without unnecessarily damaging reinforcement.

Installation, use, and stripping

Installation is carried out with nails, wood screws, or staples; with system formwork via integrated stringers and clamping elements. A level, load-bearing base, clean edge closure, and sufficient sealing of joints against cement paste are mandatory. During stripping, surfaces are protected by carefully loosening the planks and removing adherences promptly.

Protection against moisture and wear

Reusable formwork planks are stored dry, protected from direct weathering, and treated only with suitable release agents. Mechanical damage (dents, tear-outs) impairs architectural concrete quality and increases rework.

Formwork planks in deconstruction: selective concrete removal and repair

In concrete demolition and specialized deconstruction, the formwork planks themselves are usually no longer present; however, their former position can be identified by anchor patterns, joint runs, and surface features. This knowledge facilitates targeted opening of the concrete at anchor points, construction joints, and areas with increased defect risk.

Targeted exposure of anchor points

To remove or refurbish anchor cones, grout plugs, or stressing points, the concrete in the immediate vicinity is removed locally and in a controlled manner. Concrete crushers enable low‑vibration nibbling of edge areas, while stone and concrete splitters can hydraulically split thick wall or slab cross-sections from the inside. The power supply is provided by mobile hydraulic power units, which are made available depending on the work situation.

Gentle work on architectural concrete surfaces

In areas with high-quality surfaces, low vibration and precise edge guidance are important. Splitting technology reduces secondary damage to adjacent components, for example at edges defined by formwork planks. A controlled approach preserves concrete cover and component function.

Reinforcements, inserts, and permanent formwork

During refurbishments, permanent formwork or timber inserts may be encountered in the concrete. The material behavior differs clearly from mineral constituents; varying resistance should be expected during removal. A combination of concrete crushers and splitting cylinders ensures stepwise removability without intervening extensively in the load-bearing structure.

Interfaces to equipment and methods in demolition

Depending on the task, various tools are combined to process formwork areas, joints, anchors, and reinforcement in an orderly manner:

Concrete crushers: Selective nibbling of concrete, establishing removal edges at joints and anchor areas; useful in strip-out and cutting.
Stone and concrete splitters: Low‑vibration cross-section reduction on thick components; suitable for special operations where noise and vibration limits must be observed.
Hydraulic power packs: Power supply for mobile crushers, splitting cylinders, and other hydraulic tools.
Combination shears and multi cutters: Cutting light steel sections, anchor rods, embedded parts during selective demolition.
Steel shears: Shortening heavy reinforcement or tie anchors after opening around formwork anchor points.
Tank cutters: Special uses in industrial deconstruction, e.g., removing sheet steel inserts in combination with concrete work.

The selection depends on component thickness, reinforcement density, accessibility, and project constraints (e.g., in rock excavation and tunnel construction or during strip-out in existing buildings).

Applications: from building construction to tunnels

Formwork planks are used in walls, slab edges, foundation heads, column boxes, and special formwork. In massive structures, bridges, or tunnel inner linings they shape geometry and surface.

Concrete demolition and specialized deconstruction: Knowledge of the former formwork and anchor patterns helps define deconstruction stages and cut lines. Concrete crushers enable controlled openings at joints and anchor fields.
Strip-out and cutting: When removing infill panels, edge beams, and creating subsequent openings, areas previously formed by formwork planks are processed.
Rock excavation and tunnel construction: In tunnel formwork, planks as stringer or waler systems are part of the formwork traveller; subsequent adjustments to the inner lining are preferably made with low‑vibration splitting technology.
Natural stone extraction: While no formwork planks are involved, the logic of controlled splitting corresponds to splitting technology in concrete—relevant for combined deconstruction of foundations and in-situ rock.
Special operations: In confined conditions, in sensitive existing buildings, or under operating conditions, a low-noise, low‑vibration approach with hydraulic hand tools is advisable.

Typical damages, causes, and effects

Formwork planks are exposed to high stresses during the construction phase. Typical phenomena and their effect on the finished component:

Swelling and warping: Moist wood-based materials can deform; the result is wavy concrete surfaces or uneven joint widths.
Breakouts and impressions: Local damage to the plank transfers as voids or edge spalling into the concrete.
Contamination and release agent residues: Stains, adhesion problems, and uneven pore patterns are possible.
Insufficient anchoring: Joints opening, bulging under fresh concrete pressure, dimensional deviations.

During deconstruction, these traces help read joint runs and anchor axes and open them in a targeted way instead of removing large areas.

Planning, design, and quality assurance

Forward-looking planning reduces rework and facilitates later alterations:

Sizing of stringer spacing and plank cross-sections based on fresh concrete pressure.
Definition of anchor layouts with regard to accessibility and later use (e.g., avoiding anchors in future opening areas).
Defined joint layout for the desired surface appearance.
Inspection and maintenance plan for reusable planks, including documentation of damage.

Measurements of flatness, porosity, and joint position serve for acceptance. In case of deviations, local rework is possible; in massive areas the use of concrete crushers is recommended for controlled corrections.

Safety and work preparation

Working with formwork and during deconstruction requires prudent procedures. In general:

Check formwork stability before every concrete pour; understand load paths.
Use personal protective equipment; consider crushing and puncture hazards at plank edges.
When stripping, account for load-bearing functions and residual loads; do not release components prematurely.
During deconstruction minimize vibration, noise, and dust; for sensitive structures prefer hydraulic, low‑vibration methods.
Observe legal and occupational safety requirements; define project-specific protective measures.

If there is uncertainty regarding load-bearing capacity or the removal sequence, plan for structural assessments and strengthening measures. All information is to be understood as general and does not replace project-specific planning.

Sustainability and reuse

Formwork planks can be used over many cycles if properly maintained. This reduces material consumption and waste. During deconstruction, wood fractions are collected separately; metal components such as anchors or screws can be efficiently separated with steel shears or combination shears. For concrete corrections, precise, selective procedures increase the share of recyclable fractions.

Practice-oriented tips for planning and deconstruction

Deliberately arrange plank joints: regular grids make it easier to later locate anchor axes.
Document anchor cones: layout plans save time during alterations and reduce unnecessary removal.
For subsequent openings, reinforce edge zones or arrange joints so that cut lines run more favorably.
For interventions in existing structures, define the removal direction: guide crushers from edge to edge, position splitting wedges appropriately.
Dimension hydraulic power packs so that crushers and splitting cylinders operate in the optimal pressure range.

Through the interplay of good formwork planning and targeted deconstruction techniques, construction quality remains high, and interventions in existing structures remain manageable and controlled.