Site work is not the same as cutting steel

FRP grating is a composite of resin matrix and glass fibre. Cut it the way you cut steel and the edges chip, the laminate delaminates and the blade overheats. The cut behaves more like grinding: abrasive grains wear through fibre and resin together rather than a tooth shearing the material.

FRP conducts heat poorly, so cutting heat stays near the cut. The resin softens or scorches, the fibres lose support and the edge fuzzes. Too fast a feed, a dull blade or the wrong speed all widen the cut and leave a pale, ragged edge.

Before any site work, confirm three things: whether the grating is moulded or pultruded, whether the resin is orthophthalic, isophthalic or vinyl ester, and whether the surface carries a grit layer. These three decide the blade, the feed and the sealing material.

Blade choice and dust control

Diamond blades or carbide abrasive blades are the usual choice. Ordinary woodworking tooth blades are cheap, but they tear fibres, overheat and chip the edge, so they are a poor choice for visible or load-bearing parts.

Speed and feed must work together. Too high a speed with too slow a feed concentrates heat in one spot and scorches the resin; too low a speed with too fast a feed pulls fibres out before they are cut. Try a short test cut at the blade maker's settings and check the edge and the heat before running the batch.

Dust control is the part most often skipped on site. Glass fibre dust irritates skin and airways, so dry cutting should use dust extraction or a water mist, and the operator should wear a dust mask, goggles and gloves with long sleeves. Keep the cutting area away from coating or bonding work so dust does not settle on prepared surfaces.

Cutting direction and feed

Chip-out follows the exit side of the blade. A circular saw exits upward, so good face down and waste face up protects the visible side; where both faces show, masking tape or a sacrificial board on the exit face reduces chipping noticeably.

Fibre direction matters too. Pultruded grating carries fibres along the length of the profile, so a cross cut has to sever whole bundles and chips more easily than a rip cut; slow the feed and use a sharp abrasive blade for a cleaner cross cut.

Support matters as much as the blade. Pack both sides of the cut so the grating cannot sag, pinch the blade or chip; a sagging panel can even jam the saw. On large sheets, clamp a straight edge and push the saw through at a steady speed without stopping mid-cut.

Circular saws, reciprocating saws and jigsaws all have a place. A circular saw suits long straight cuts, a reciprocating saw suits short cuts close to a wall, and a jigsaw suits corners and shaped openings at slow speed. Finish the cut with a file or abrasive paper to remove burrs and loose fibre. Detailed site cutting and drilling methods are set out in the grating fabrication guide

Where to place openings and cuts

Keep openings inside the open squares of the grating where possible and avoid cutting load-bearing bars. Moulded grating carries load bars in one direction; pultruded grating carries deep vertical load-bearing bars. In either type, cutting a load-bearing member reduces the section and calls for reinforcement as the maker advises.

Leave enough distance from a hole to the panel edge and between holes. Too little material left around a hole can crack when a fastener is tightened or when temperature moves the panel. Edge distances differ between makers, so use the product data and the project specification rather than rule of thumb.

Do not run several holes into one long slot. Where a long opening is needed, drill it in stages and finish the edges, or frame the opening with FRP profile or stainless angle so load returns to the bars on each side. Seal every cut afterwards, and leave clearance around pipe penetrations for thermal movement.

• Do not open holes with a hammer or pry bar; impact cracks the resin.
• For a large hole saw, drill a pilot first and cut halfway from each face to limit exit chipping.
• Keep holes away from support points where there is too little material for the fastener.
• Trim loose fibre from the cut edge before sealing.
• Check hole spacing after drilling; correcting before installation is cheaper than afterwards.

Sealing cut edges and ends

A cut exposes the ends of the glass fibres, and water or chemicals can travel along the fibre-resin interface. Over time this shows as whitening, blistering or delamination, so every site cut should be sealed rather than left open.

The sealant must suit the original resin. Orthophthalic grating takes an orthophthalic or isophthalic sealing putty, and vinyl ester grating takes a vinyl ester putty; the wrong system bonds poorly and may lift within months. Clean, dry and lightly abrade the cut before sealing, and cover the full end face including the top and bottom edges.

Sealing is not structural reinforcement. It restores resistance at the surface but does not replace an opening frame or a reinforcing member. Structural openings, large holes and stair nosings need separate support. Allow the stated cure time before the edge sees water or load. To match edge treatment with the grating specification, see the FRP grating specification data

Stair treads and edge trim

A site-cut tread should not use the cut edge as the stair nosing. The exposed fibre end wears quickly under foot, fuzzes, and can scratch shoes or skin; fit a proprietary anti-slip nosing, an edge profile or the maker's trim instead.

Yellow warning edges are usually supplied as anti-slip nosing strips, fixed by adhesive or mechanically. Before bonding, abrade, clean and dry the surface and follow the adhesive data for temperature and open time; where mechanical fixings are used, specify stainless steel and isolate it from the grating to avoid galvanic corrosion.

All treads on one stair should match. Make one sample tread on site, confirm width, nosing position and fixing holes, then work to the sample. Fixing method, nosing overhang and opening positions can be adapted to the project; common details are shown in the stair tread solutions

Tolerances and acceptance

Site cutting normally holds wider tolerances than factory cutting. Length, width, diagonals, flatness and cut squareness follow the project or the maker's data; where a dimension affects the installation gap, leave two or three millimetres on site and trim at fitting.

Acceptance looks at a few things: whether the cut has delamination or chipping beyond the agreed limit, whether hole positions are within tolerance, whether sealing is continuous, and whether the panel is distorted. Trial-fit critical panels before installation and check the gap to support beams, handrails and neighbouring panels.

Temperature belongs in the calculation. FRP expands more than steel, so long panels move visibly over a wide temperature range; correct cut sizes for the installation temperature and use slotted holes or clearance so panels do not jam against each other.

Safety and site organisation

Screen the cutting area and post warnings, and keep others clear. Never remove the blade guard, pack the panel solidly, and keep hands away from the line of cut. Clear dust and offcuts daily so they do not build up or become airborne again.

Store uncut grating flat on bearers spaced closely enough to prevent long-term distortion, and cover outdoor stacks against prolonged UV and rain. Mark cut panels with direction, position and number so the load direction is not reversed at installation.

Site fabrication looks like a small job, but it decides how the edges age and how the finished installation looks. Blade, direction, support and sealing done properly bring a site-cut panel close to a factory-cut one.