Decide five things before cutting

Most FRP grating problems on site come from layout and fixing decisions, not from the material. Before cutting, confirm the load-bar direction, joint positions, expansion allowance, support spacing and fastener locations.

Pultruded grating carries load on one axis only, so its load bars must run across the supports, never along them. Moulded grating carries load in two directions but still has a stronger direction; let that direction span the shorter distance. Panel joints must land on a support; a joint hanging in mid-air will crack.

Expansion gap: about 3 mm per metre at 40°C

For the same temperature change, FRP moves about twice as much as steel. A panel wedged against a wall, or two panels wedged against each other, will arch and lift as it warms, and the fasteners will crack.

The published rule of thumb is about 3 mm of expansion gap per metre of panel at a 40°C temperature range. Leave gaps between panels, between panel and wall, and between panel and fixed structure. Take the upper value when installation is near the annual minimum temperature, reduce it when near the maximum, but never set it to zero.

Supports and fixing: every support, every free edge

Grating that is merely laid down will move underfoot, lift in wind and creep out of position. Set support spacing from the load and deflection table using the actual span, not from the panel size that happens to be on order.

Fix every support and every free edge. An unfixed edge is both a trip hazard and a sail. Use moulded mounting clamps for moulded grating and pultruded clamps or J-bolts for pultruded grating. Do not put screws through the load bars, and keep fastening points clear of areas that may later be cut away.

Do not over-tighten. FRP has much lower compressive strength than steel; stop as soon as the panel is held. Radial cracks around a fastener are almost always caused by over-tightening. Match the metals too: stainless structure with stainless fasteners, galvanised with galvanised. Mixing them in a wet environment creates galvanic corrosion, and the fastener is usually what disappears.

Cutting: measure, kerf and tools

Measure an opening at several points and use the smallest actual dimension; openings are rarely square, and a panel cut to the drawing may not fit. Check the panel itself for square by measuring diagonals. Moulded panels have moulding tolerance, and a 5 mm diagonal difference shows at the joint.

Mark the face and, where the tool allows, cut from the face; chipping occurs on the exit side. Allow for kerf: a typical abrasive blade removes 3-4 mm.

For straight cuts, use a circular saw with a diamond or carbide abrasive blade. Use a jigsaw for curves and small openings, a reciprocating saw for trimming installed panels, and an angle grinder only for small adjustments. Never use flame or any heat-cutting method; heat destroys the resin. Cutting produces glass-fibre dust, so wear a dust mask, sealed goggles, gloves and long sleeves, and work outdoors or with dust extraction.

Seal every cut edge

This is the most important installation rule. Moulded and pultruded panels have a resin-rich surface skin; cutting exposes bare glass fibre. The resin matrix is the chemical barrier, while the fibre itself has low chemical resistance and wicks liquid along its length. Once the medium travels along the fibres, the panel delaminates from the inside while the surface may still look sound.

Seal with the same resin family as the panel, whether orthophthalic, isophthalic, vinyl ester or phenolic, and cure it before service. A compatible sealant may be acceptable in mild duty, but a resin coating is the correct approach for chemical service. The same applies to drilled holes, notches and any other place where the surface is broken: if fibre is visible, seal it.

Match the treatment to the duty: sealing is recommended for water, seawater and neutral salts; mandatory for dilute acids and alkalis; mandatory with a matching resin for strong acids, strong alkalis and oxidisers; and must use a food-grade system in food and drinking-water areas.

Stair treads, walkways, openings and handrails

Use contrasting colours for the top and bottom treads; the last step is where people most often miss their footing. Treat the tread nosing, usually with a tread cover or anti-slip strip rather than a metal angle, which corrodes against the panel. Use a grit surface in wet or oily areas and a smooth surface where trolley wheels or cleanliness demand it.

Every penetration and opening needs edge restraint. An unrestrained opening is both a crack starter and a foothold trap. Keep walkway joints off the panel joints where possible; where a joint must cross, add a support beneath it.

FRP handrails have a lower modulus than steel, so posts must be closer together to feel equally rigid. Fixing the rail to the structure is stiffer than fixing it to the grating and keeps load out of the panel. If it must fix to the grating, add a load bar underneath rather than relying on the clamps alone.

Common mistakes

Installing before sealing the cuts leads to delamination from the edge inward. Pultruded load bars installed the wrong way deflect under design load. No expansion gap causes arching and lifted fasteners. Over-tightened fasteners crack the panel radially. Stainless fasteners on galvanised steel leave the fastener to corrode first. A woodworking blade burns the resin and chips the edge. Cutting an unsupported panel tears along the cut. A joint left in mid-air opens and cracks.

All of these are free to avoid and expensive to repair, usually costing a panel replacement and downtime.

Order cut-to-size and remove the site risk

Send a dimensioned sketch; writing dimensions on a photograph of the opening is often clearer than a formal drawing. The supplier can cut to tighter tolerance, seal every cut with the matching resin and number each panel to the sketch, so the delivery fits straight into place.

State the medium and temperature with the order so the sealant matches the duty, not just the panel. The full fabrication and installation sequence is in the FRP grating fabrication guide

Mesh, panel size and resin systems are in the FRP grating specifications guidedeflection data in the FRP grating load capacity guide

The short rule

Lay out before cutting, land joints on supports, leave enough expansion, do not over-tighten the clamps, and seal every cut with the matching resin.