Can sandwich panels be used as formwork in concrete construction?

compoform · 24 Aug 2026

Sandwich panels can be used as formwork in concrete construction, but with important limitations. Their suitability depends on the panel specification, the hydrostatic pressure generated by the wet concrete pour, and whether the application calls for temporary shuttering or permanent stay-in-place formwork. The questions below unpack the key considerations any engineer or contractor should evaluate before specifying composite panels for this use.

What types of formwork are used in concrete construction?

Concrete formwork falls into two broad categories: temporary shuttering, which is removed after the concrete cures, and permanent or stay-in-place formwork, which remains as part of the finished structure. Within those categories, the most common materials are timber and plywood, steel, aluminium, and fibre-reinforced polymer (FRP) composites.

Plywood and timber remain the most widely used temporary formwork materials on European construction sites because they are low-cost and easy to cut on site. Steel and aluminium systems are preferred for large-scale or repetitive pours where dimensional precision and reuse cycles justify the higher upfront cost. Composite and polymer-based panels have gained ground in recent years as permanent formwork, particularly in construction and infrastructure formwork applications where the panel contributes insulation, moisture resistance, or a finished surface to the completed structure.

Stay-in-place composite formwork is especially relevant in infrastructure projects, retaining walls, and prefabricated building elements, where removing the shuttering after the pour is impractical or adds unnecessary cost. In these scenarios, the formwork panel becomes a structural or functional layer of the finished assembly rather than a disposable tool.

What properties make a material suitable for concrete formwork?

A material suitable for concrete formwork must resist the hydrostatic pressure of wet concrete without deflecting, absorbing moisture, or delaminating. The four properties that matter most are bending stiffness, compressive strength, moisture resistance, and surface release quality.

Wet concrete exerts significant lateral pressure on vertical formwork faces, and that pressure increases with pour height and pour rate. A panel that deflects under load will produce a curved or uneven concrete surface, which is structurally and aesthetically unacceptable. Bending stiffness is therefore the primary mechanical requirement.

Moisture resistance is equally important. Formwork materials that absorb water swell, warp, and weaken over repeated use cycles. Traditional plywood degrades rapidly in wet conditions, which is why it typically needs replacing after a limited number of pours. Composite and thermoplastic panels that are fully waterproof maintain their geometry and mechanical properties across many cycles.

Surface release quality determines how cleanly the panel separates from the cured concrete. Smooth, non-porous surfaces require less release agent and produce a better concrete finish. Panels with textured or porous surfaces bond more aggressively to concrete and are harder to strip without damaging either the panel or the concrete face.

Can sandwich panels withstand the pressure of wet concrete?

Sandwich panels can withstand the pressure of wet concrete, provided the panel specification is matched to the pour conditions. The critical variables are panel thickness, core density, skin stiffness, and the span between support points. A correctly specified sandwich panel will resist the hydrostatic pressure of a standard concrete pour without measurable deflection.

The sandwich construction principle works in formwork’s favour. The stiff outer skins carry bending loads in tension and compression, while the core resists shear across the panel thickness. This makes sandwich panels structurally efficient relative to their weight, delivering high stiffness without the mass of solid timber or steel.

However, the pressure exerted by wet concrete is not trivial. A 1-metre-high vertical pour of standard concrete generates roughly 24 kPa of lateral pressure at the base. Taller pours, faster pour rates, and vibrated concrete all increase this figure. A panel that performs adequately as a floor or wall cladding panel may not have sufficient bending stiffness for a deep vertical formwork application without additional support framing.

The answer, in practice, is that sandwich panels are well-suited to stay-in-place formwork for shallow pours, horizontal slab decking with close support spacing, and wall panels where pour height is controlled. For deep vertical pours without intermediate support, the panel specification needs careful structural review before use.

What are the advantages of sandwich panels over traditional formwork?

Sandwich panels offer four concrete advantages over traditional timber or steel formwork: lower weight, longer service life, moisture resistance, and a finished surface on the concrete face. Each of these translates directly into reduced cost or improved performance on site.

Weight is the most immediate benefit. Composite sandwich panels are significantly lighter than equivalent steel or thick plywood shuttering. Lighter panels are faster to handle, position, and strip, which reduces labour time per pour. On multi-storey projects or scaffolded structures, the reduced load also matters for the supporting structure.

Service life is where the economics become compelling. Plywood formwork typically survives between 5 and 20 uses before surface degradation makes it unsuitable for fair-faced concrete. Composite panels, being waterproof and dimensionally stable, maintain their surface quality across far more cycles. Over a project lifecycle, fewer panel replacements reduce both material cost and waste.

For stay-in-place applications, the panel’s own properties add functional value to the finished structure. A thermoplastic sandwich panel left in place after the pour can contribute thermal insulation, moisture protection, or a decorative surface finish, eliminating separate finishing trades. This is a meaningful advantage in prefabricated wall systems and insulated concrete form construction.

Are there limitations to using sandwich panels as formwork?

Yes. Sandwich panels have real limitations in formwork applications, and specifying them without accounting for these risks leads to panel failure or poor concrete quality. The main limitations are sensitivity to point loads, core compression under fasteners, chemical compatibility with concrete release agents, and cost relative to disposable plywood.

Point loads from ties, clamps, and fasteners concentrate stress at specific locations on the panel face. In sandwich construction, the skin is thin and the core beneath it must resist the compressive load transferred through the fastener. If the core density is too low, the fastener pulls through or the skin dimples, compromising both the panel and the concrete surface. Panels intended for formwork use need a core specification that accounts for these localised loads, not just distributed pressure.

Chemical compatibility is a less obvious but important concern. Some concrete release agents and curing compounds contain solvents that attack certain thermoplastic materials. Before specifying a composite panel for formwork, the release agent chemistry should be checked against the panel’s skin material to confirm compatibility.

Cost is also a genuine constraint. Composite sandwich panels carry a higher unit price than commodity plywood. For temporary formwork that will be used only a handful of times, the economics rarely favour composite panels unless the weight saving or surface quality justifies the premium. The business case is strongest for high-reuse temporary formwork or stay-in-place applications where the panel’s long-term properties add value.

What sandwich panel specifications are recommended for formwork applications?

For formwork use, the recommended sandwich panel specification prioritises high skin stiffness, a dense core, a smooth non-porous surface, and waterproof construction throughout. Panels with glass-fibre-reinforced thermoplastic skins and a PP-foam or PP-honeycomb core are well-suited to this application when correctly specified.

Skin architecture matters significantly. A multi-ply glass-fibre laminate with fibres oriented in both the 0° and 90° directions distributes bending loads evenly across the panel face, regardless of pour direction. Cross-ply laminates are particularly useful here because they equalise mechanical properties in both orientations, meaning the panel performs consistently whether the dominant load runs along or across its length.

Core density should be selected based on the expected contact pressure and fastener loads. Higher-density cores resist point loads more effectively and deflect less under distributed pressure. For formwork applications, a PP-foam core in the upper density range, or a PP-honeycomb core, will generally outperform lower-density foam cores that are adequate for wall cladding but marginal under concrete pressure.

Surface finish is the final specification consideration. A smooth PET-film surface on the concrete-contact face provides a non-porous, low-adhesion interface that releases cleanly from cured concrete and is easy to clean between pours. This surface also protects the glass-fibre skin from direct contact with the alkaline concrete environment, which can degrade unprotected fibres over time.

Panel thickness should be determined by structural calculation based on pour height, pour rate, and support spacing, rather than by rule of thumb. For stay-in-place horizontal decking with close joist spacing, panels from 17 mm to 30 mm thickness are a practical starting range, but the specific load case must be confirmed before finalising the specification.

How Compoform Can Help with Sandwich Panel Formwork

We manufacture fully custom thermoplastic sandwich panels designed to meet the specific mechanical and surface requirements of your application. For formwork and construction applications, we work with you to define the right panel configuration from the outset, rather than adapting a standard product that was designed for a different load case.

Custom core and skin specification: We offer PP-foam cores across six density grades and PP-honeycomb cores, combined with multi-ply glass-fibre skins in cross-ply or unidirectional layups, so the panel stiffness and point-load resistance can be matched to your pour conditions.
Large-format panels: Our production line manufactures panels up to 13,500 mm × 2,950 mm, which reduces the number of joints in large formwork faces and improves the quality of the finished concrete surface.
Smooth PET-film surface finish: Available on wall- and formwork-oriented panels, this finish provides a clean concrete-contact face that releases well and protects the fibre laminate from the alkaline concrete environment.
Application engineering support: Before production, we review your design, assess the load case, and confirm the panel configuration is appropriate for your specific pour geometry and support arrangement. We flag potential issues before they become site problems.

If you are evaluating composite panels for a formwork or stay-in-place construction application, speak with our engineering team about your project about the specific requirements of your project. We will review the pour conditions, recommend a panel configuration, and support you through integration, not just the initial order.