Resin for FRP Moulded Gratings and Walkway Platforms

Grating fabricators mould walkway and platform panels, stair treads, trench and drain covers, catwalk sections and hand-cut infill pieces, usually in standard panel sizes that are cut and fitted on site. The same shop often makes the handrails, kick plates and ladder sections that go with them.

Pultruded gratings and structural sections are a different process entirely — bars pulled continuously through a heated die rather than laminated in a mould. That work is covered by the pultrusion guide and uses Pultrusion Grade Resin (SPR 401 PT).

A grating panel is a thick, resin-rich laminate with a lot of edge and corner detail, so the resin has to wet chopped strand mat out into narrow bar sections without starving the corners, and then cure through that thickness at workshop temperature. GP Clear Resin at 350–450 cPs with a gel time under 8 minutes and GP Yellow Resin at 450–600 cPs with a 10–15 minute gel time are the general-purpose grades for that; the thicker, slower grade helps when a full panel is laid up in one pass.

Where the grating stands in a wet or chemically active area, ISO Polyester Resin is the isophthalic laminating grade — 500 cPs, a 15-minute gel time, 40% styrene and a 90 °C heat deflection temperature in its TDS summary, which is resin data rather than a service limit. Vinyl Ester Resin is the route for chemical service beyond what a polyester laminate is specified for. All three cure at room temperature with MEKP hardener and cobalt octoate added separately.

Panels are laid up in a grating mould: gelcoat or pigmented surface first where the finish calls for it, then chopped strand mat worked into each bar channel with resin catalysed by MEKP hardener and accelerated with cobalt octoate, added separately and never mixed together first. Layers are built up to the panel depth, consolidated so no air is trapped at the bar intersections, and cured at workshop temperature before demoulding, trimming and edge finishing.

Two process points decide most of the quality: dose the catalyst and accelerator for the shop temperature that day so a thick section does not run away on exotherm, and keep the mould release routine consistent so panels come out clean. FRP polyester pigment is added where the grating is coloured for safety marking, and GP Gelcoat Resin is used where a moulded surface finish is wanted.

A grating is specified by load class, span, deflection under load, open area and slip resistance. None of those comes from the resin alone — they come from the panel design, the bar depth and spacing, the glass content and the grating maker’s own testing. This site publishes no load table, span chart, slip rating or fire rating for a finished grating, and a plant specification asking for one should be answered with the fabricator’s test data rather than with resin data.

• A fire requirement. Plant rooms and enclosed walkways sometimes specify fire-retardant laminates. Fire Retardant Resin is the halogenated grade and ISO Fire Retardant Resin the halogen-free, ATH-filled isophthalic one; the requirement is met by the finished, tested part, not by the resin alone. The fire-retardant guide covers that work.
• Aggressive chemical service. Name the chemical, its concentration and the temperature, and compare Vinyl Ester Resin against ISO Polyester Resin; no compatibility chart is published here.
• Continuous profiles instead of moulded panels. Pultruded bars and sections are Pultrusion Grade Resin (SPR 401 PT) work — see the pultrusion guide.
• Gratings around a cooling tower. The tower itself and its walkways are covered in the FRP cooling tower guide.