Fine-mesh grating overlays

What it is

Standard steel bar grating has openings of roughly 30 × 100 mm, which suits drainage, light and ventilation but lets nuts, bolts, small tools, welding rods and process debris fall to the level below. On multi-level plant, above conveyors, or over routes where people work or pass, that is a recognised dropped-object hazard. A fine-mesh grating overlay is a panel of fine mesh or perforated sheet clamped on top of the existing grating, reducing the effective opening without removing or replacing the floor.

World Steel fabricates overlay panels to the existing grating layout recorded in a site survey, so panel joints follow the grating panel joints and access hatches remain operable. Panels are held down with clamps that hook under the bearing bars, so there is no welding on site. Overlays are commonly combined with handrail infill panels and clamp-on toe boards so that the floor, the edge and the barrier are all closed to the same criterion.

Types and options

The opening is not a standard size: it is chosen to the site owner's criterion, often defined by a test object or ball of a stated diameter that must not pass. Slip resistance of the top surface should also be considered – perforated sheet with a raised pattern or a grit finish can be specified where the site requires a rated surface.

Design and compliance

An overlay changes the walking surface, so three points are checked. First, trip hazards: panels are low profile, with tapered or bevelled edge strips where the overlay meets open grating. Second, slip resistance: the surface is selected to the site's requirement, with reference to AS 4586 in Australia. Third, the floor: the overlay adds a small dead load and, more importantly, can hold water, ice, dust or product that would otherwise fall through, so drainage and cleaning are considered in the layout.

Platform and walkway geometry still follows the governing code – OSHA 1910 Subpart D, AS 1657-2018 (walkway clear width at least 600 mm) or EN ISO 14122-2 (clear width at least 600 mm, preferably 800 mm). No load or test rating is claimed for the overlay; the grating beneath remains the load-carrying floor. See the gratings and access article and steel grating solutions for background.

Fabrication and finishing at World Steel

Mesh and sheet are cut to the panel schedule, framed with flat bar or folded edges and fitted with clamp hooks matched to the bearing-bar depth and pitch. Welding follows qualified procedures under AWS D1.1, AS/NZS 1554.1 or EN ISO 3834-2, and stainless items follow AWS D1.6 or AS/NZS 1554.6. Carbon steel panels are hot-dip galvanised by qualified galvanisers to AS/NZS 4680, ASTM A123 or EN ISO 1461; stainless panels are pickled and passivated. Panels are numbered to the grating layout and packed for export.

Installation and site notes

• Survey the grating: panel sizes, bearing-bar depth and pitch, hatches, penetrations and kick plates.
• Clean the grating, place the overlay and engage the clamps under the bearing bars.
• Check edges for trip lips and that hatches and removable panels still open.
• Lift overlays periodically to clean beneath them and inspect the grating.