The choice between moulded and pultruded FRP grating is one of the most common specification questions in industrial infrastructure. They look similar, they're made from the same base materials, and they're both marketed as corrosion-resistant. But they're manufactured differently, they behave differently under load, and they're suited to very different applications.
How Each Type Is Manufactured
Moulded FRP grating is produced by hand lay-up or resin transfer moulding. Continuous glass fibre rovings are woven over and under each other in a grid pattern — alternating in two directions — inside an open mould. Resin is applied, the assembly is cured, and the result is a panel where the glass fibres run in both the longitudinal and transverse directions simultaneously.
Pultruded FRP grating is produced by the pultrusion process. Individual bearing bars are manufactured first — glass fibres are drawn through a resin bath and a heated die, producing a continuous structural section of consistent cross-section. The bearing bars are then connected at intervals by interlocking crossbars to form the finished grating panel.
Key Manufacturing Difference
In moulded grating, all fibres are shared between both directions simultaneously — so load in any direction uses the same glass. In pultruded grating, the bearing bars carry load independently in the span direction — they can be heavily reinforced in exactly the direction required.
Structural Performance The Critical Difference
This is where the two types diverge most significantly, and where specification errors are most costly.
Moulded Grating Load Behaviour
Because the fibres run equally in both directions, moulded grating distributes load in two directions. It behaves more like a plate than a beam. This makes it strong in applications where load can come from any direction or where the grating spans in two directions simultaneously. However, the bi-directional glass distribution means no direction gets the full reinforcement benefit — load capacity per unit weight is lower than pultruded.
Pultruded Grating Load Behaviour
Pultruded bearing bars behave as independent beams spanning in one direction. Because the glass fibres run the full length of the bar without deviation, the mechanical properties in the span direction are significantly higher than moulded grating of the same depth. For longer spans and higher point loads, pultruded grating achieves the required deflection limit with fewer bars or greater span between supports.
Practical implication: For a 1500 mm span at the same deflection limit, pultruded grating will typically use a shallower section — or carry a higher load at the same section depth — compared to moulded grating. This directly affects support structure design and overall weight.
When to Specify Each Type
Use Moulded FRP Grating When:
- Support spacing is 600–1000 mm — moulded grating performs excellently at shorter spans and the bi-directional strength is well-utilised.
- Complex cutouts are required — penetrations for pipes, handrail posts, and equipment legs can be cut to any shape with standard angle grinders without compromising adjacent sections.
- The platform has irregular geometry — moulded panels can be field-cut to fit awkward shapes, stairways, and non-rectangular openings on site.
- First cost is the primary constraint — moulded grating is typically lower cost for equivalent section depths.
- Chemical immersion resistance is critical — the continuous resin matrix in moulded grating has no preferential fibre-resin interfaces to delaminate under long-term immersion in aggressive chemicals.
Use Pultruded FRP Grating When:
- Spans exceed 1000–1200 mm — pultruded bearing bars achieve the required deflection limits at spans where moulded grating would require intermediate support.
- Point loads are high — concentrated loads from wheeled equipment, trolleys, or pallet jacks are better handled by pultruded beams than moulded plate behaviour.
- Dead load must be minimised — pultruded grating's higher strength-to-weight ratio reduces the load on supporting steelwork, which can reduce structural costs on new-build platforms.
- Precise deflection control is required — the unidirectional fibre layout gives more predictable and calculable deflection values for structural sign-off.
Specifying Correctly — What to Include
A complete FRP grating specification should include the following items to allow manufacturers to price and supply the correct product:
- Grating type — moulded or pultruded (do not leave this unspecified)
- Resin type — isophthalic polyester (standard corrosion resistance), vinyl ester (for acids, solvents, or offshore), or phenolic (fire-rated)
- Section depth — typically 25 mm, 38 mm, or 50 mm, determined by span and load
- Mesh opening — 38×38 mm (standard), 50×50 mm (where drainage is critical), or closed top
- Anti-slip surface — gritted top surface (quartz aggregate), meniscus (moulded), or smooth for clean-room / food environments
- Colour — yellow (safety areas), grey (general), green (environmental), or custom
- Panel size — specify if standard panels or project-specific cut sizes are required
Key Takeaway
Moulded and pultruded FRP grating are both corrosion-resistant and non-conductive — but they are structurally different products. Moulded for short spans, complex cutouts, and lower cost. Pultruded for long spans, high point loads, and minimum section depth. Specifying the wrong type for the span results in either excessive deflection or unnecessary cost.