What can be repaired and what cannot

How much of a damaged panel can be repaired depends on where the damage sits. Surface scratches, worn resin, small areas of exposed fibre and chipped edges are surface problems that cleaning and sealing can restore; a broken bearing bar, a crushed node or wide delamination reaches the structure and must be treated as a structural item.

A simple test is whether the damage crosses a bearing bar. A small notch along a cross bar usually does not affect capacity, because the cross bar mainly connects and distributes; a cut or crack through a bearing bar severs the load path and cannot be painted back with resin.

The cause matters as much as the damage. Impact damage is local and a proper repair normally restores service; a crack caused by long-term overload, a settling support or chemical attack needs the root cause fixed first, or the repair will fail again.

Assessment: load path and extent

Assess before touching anything: position, size and depth of the damage, whether it lies on a bearing bar, how close it is to a support, and whether people or equipment pass underneath. The result decides between a patch, a partial panel replacement and a full replacement.

Cracks in a bearing bar need particular care. The crack tip concentrates stress and will keep growing under load, so the remaining capacity cannot be judged from the visible length of the crack.

The assessment also has to confirm the original design conditions: span, support spacing, load class and fixing method. Without them there is no way to show that a repaired panel still meets the original duty, and a conservative full replacement is the only safe answer. For support spacing, see FRP grating support spacing

Partial replacement: marking, cutting and removal

A partial replacement starts with cutting the damaged area to a regular shape, usually a rectangle or square, with the edges landing between two cross bars rather than on a bearing bar. Mark with a try square and keep the cut edges straight so the patch can overlap cleanly.

Cut with a fine-tooth blade or a diamond disc and do not force the speed. A fast cut overheats the resin near the kerf, discolours or delaminates it, and leaves burrs and chipped edges.

Before removing the old panel, check how the surrounding panels are fixed so cutting vibration does not loosen adjacent clips. Clear the offcuts promptly and vacuum the dust at the cut; resin dust must not be left on the support beams. For general working rules, see FRP grating fabrication and cutting

Patch size, overlap and fixing

The patch should extend at least one bearing bar spacing beyond the opening on every side, so it can pass load into the intact bars next to it. A patch that is too small concentrates load at the new joint, and the seam opens quickly.

The overlap faces must be flat; where needed, add a stainless backing plate or a bearer. Fix the overlap with clips or bolts at the maker's spacing, with the edge row slightly closer together.

Match the original fixing method. Where clips were used, the patch uses the same clip; where bolts were used, fit washers of matching material so stainless and carbon steel do not touch and start galvanic corrosion. For fastener choice, see FRP grating fasteners and installation

Resin patching: where it applies

Resin patching suits shallow defects: hollows no deeper than a quarter of the panel thickness, chipped edges, small areas of exposed fibre and damaged banding. Its job is to restore the resin protection layer, not to carry structural load.

Grind the damaged area to a taper, remove loose resin and debris, wipe with acetone or the specified cleaner and let it dry completely. Mix the resin at the maker's ratio, add filler to a paste consistency, and build up in thin layers rather than one thick fill.

Cure time depends on temperature; cold weather extends it, and the repair should not be force-dried with heat to save time. Sand the cured patch flat and blend it into the surrounding surface; on an anti-slip area, broadcast matching grit onto the surface before it is fully cured.

Edge sealing and watertight closing

Every cut and drilled edge must be sealed. Sealing locks off the cut fibres and stops water travelling along the fibre-resin interface; an unsealed cut is the first place where whitening and delamination appear.

The sealant has to be compatible with the original resin. Polyester grating takes a polyester edge resin and vinyl ester grating takes vinyl ester; mixing them can bond poorly, show nothing at first and start to peel months later.

Apply two coats, the first to penetrate and the second to film, with a little extra at corners. After sealing, check for pinholes and misses, particularly along the upper and lower edges of the cut and at the returns.

The limits of structural strengthening

Some damage cannot be solved with a patch and needs strengthening or replacement: more than one broken bearing bar, radial cracks at a node, or a full-length delamination along an edge. These call for an added bearer, extra supports or a new panel.

Strengthening is not a matter of adding thickness. A steel beam under the grating changes drainage and ventilation and introduces a new corrosion point; a plate on top adds weight and a trip hazard. The strengthening scheme is confirmed by the designer, not decided on site.

Material compatibility matters here too. A stainless stiffener against a carbon steel support forms a galvanic couple, and aluminum against FRP can also cause trouble when wet; isolating washers and sealant are chosen to suit the materials in contact.

Load checking after repair

A completed repair needs a load check covering at least visual inspection, fixing inspection and proof loading. The visual check looks for hollow patches and incomplete sealing; the fixing check looks at bolt torque and clip contact.

Proof load in stages up to the original design load and watch the deflection at mid-span and at the joint. Where instruments are available, measure with a dial gauge and compare against an unrepaired panel of the same span; a clearly larger deflection means the patch is not transferring load.

Record the result: loading method, load values, deflection readings and the people involved. A repair without a record is hard to defend at a later acceptance or in an incident investigation.

Records, aftercare and common mistakes

The repair record should state the damage location, the cause as judged, the method, the material batch and the date, with before and after photographs. It is both a maintenance file and a reference for the next time the same problem appears.

Put the repaired area on the inspection route, monthly for the first three months, to confirm there is no new cracking, hollowing or water ingress; sealant and patches are most vulnerable while they cure, and early faults are the cheapest to fix.

The common mistakes are: using a cut without sealing it, substituting ordinary epoxy for the specified edge resin, making the patch too small, drilling straight through a bearing bar, and skipping the load check. Any one may get away with it; together they make the repair fail.