A specification controls delivery, not marketing

The job of an FRP grating specification is not to repeat a product brochure. It is to turn the project's service conditions into clauses a supplier can price and an inspector can measure. Written well, it makes quotations comparable; written badly, it means nothing.

A specification has to do three things: convert the duty into parameters, write each parameter as a measurable sentence, and turn whatever cannot be measured into a procedure, such as samples, reports, sampling rates and acceptance methods.

The most common failure is not writing too little but writing clauses that contradict each other. The process is named as pultruded while the same text demands equal strength in both directions; the surface is named as grit while the same paragraph calls for barefoot use. Contradictions like these survive tender review and only surface on delivery.

Duty first, product second

The first group of numbers is geometry: span, support beam spacing, support width and the direction the grating is laid. These decide depth and process directly, and they decide whether the manufacturer's load table can be applied at all.

The second group is load: uniform load, concentrated load, line load, and whether forklifts, pallets, maintenance point loads or falling impact occur. State the value and the position instead of phrases such as normal industrial loading that cannot be measured.

The third group is environment: medium, concentration, temperature, contact mode, cleaning agents and UV exposure. The fourth is safety: fire class, slip class, and whether insulation or earthing is required.

The order cannot be reversed. Choosing a panel and then changing the beams usually means the deflection is short, the supports have to be added and the programme is reworked; fixing the beams and then choosing the panel changes one parameter.

Writing resin and reinforcement

Specify the resin by family, not by adjective. The phrase corrosion resistant is not a material parameter; orthophthalic, isophthalic, vinyl ester and phenolic are. Name the family at minimum, the manufacturer's grade on important projects, and state whether a surface veil is required.

For glass, state the content range: by weight for molded grating, and roving type plus content for pultruded. Avoid phrases such as high-strength glass fibre unless a test method and an acceptance value come with them, because nothing can be checked against a phrase.

The surface veil belongs on its own line, with its material and its weight per square metre. C-glass veil resists acid well, synthetic veil resists alkali and solvents better, and polyester veil is cheap but only moderately resistant; writing surface veil and stopping there says nothing.

For matching medium, concentration and temperature, see chemical resistance of FRP grating

Surface and slip clauses

Name which of the three surfaces is required: the concave profile formed in the mould, grit bonded into the resin, or a bonded anti-slip plate. For grit, add the particle material and the size range, because those decide wear life and how fast the surface wears out soles.

Slip class needs a standard, a method and a condition. An R11 obtained under DIN 51130 on an oiled ramp is not comparable with a figure from another method, and barefoot areas need their own A, B or C class under DIN 51097.

State the specimen condition: dry or wet, and whether the contaminant is clean water, soap or oil, at what temperature. The class moves with the condition, so a report without the condition says very little.

Mesh, panel size and supports

Mesh size means the centre distance of the bearing bars and of the cross bars, plus the height and thickness of the bearing bar. Those four figures are the basis of the load table; miss one and the capacity data no longer refers to a known product.

State the standard panel size and where joints are permitted. Writing lay out on site passes the responsibility to the installer, and the result is a joint at mid-span with deflection and ponding problems to follow.

Support conditions mean beam spacing, support width and bearing length. Load tables are usually tested at a stated support width; where the real support is narrower, capacity has to be reduced instead of read straight from the table.

For openings, state the maximum size, the minimum distance from an opening to a support, the minimum spacing between openings, and whether large openings need reinforcement. Openings are the part of site work most often done wrong.

For how to set span and beam spacing, see FRP grating support spacing

Load and deflection on one basis

A load clause needs four items at least: load type, value, combination and the source of the safety factor. Uniform and concentrated loads cannot substitute for each other, and forklift duty needs a dynamic factor on top.

The deflection limit has to state the denominator and any absolute cap. Whether it is L/160, L/200 or L/100, whether a fixed cap also applies and which of the two governs, changes the answer completely for the same panel.

Record the version and date of the load table. Manufacturers revise them, and the table quoted at tender may not be the table behind the later delivery, which leaves acceptance with nothing to check against.

Fire, colour and tolerance

Fire clauses need a standard, a class and a test method. ASTM E84 reports flame spread and smoke developed; EN 13501-1 reports a class from A1 to F with added smoke and droplet classes; GB 8624 reports B1, B2 and so on. The word flame retardant on its own cannot be accepted.

Colour needs a reference number or a retained sample, plus the permitted colour difference and how it is judged. Colour is not a structural property, but it is one of the most common reasons for rejection, especially when one project arrives in several batches.

Tolerances should be listed item by item: thickness, panel width, panel length, diagonal difference, bearing bar spacing and flatness. Each needs a value and a measuring method, or the inspector is left with feel alone.

Cut edge and opening tolerances belong on a separate line. They decide whether the panel fits on site, and whether the edge seal can cover the cut face.

For the limits of site cutting and drilling, see fabrication of FRP grating

Packaging, marking and documents

Packaging clauses cover stack height, bearer position, whether UV-resistant wrapping is required and how lifting points are marked. Sea freight also needs the pallet treatment stated so the shipment is not held at the port over timber packaging.

Marking should reach every bundle or panel: batch number, size, resin type, production date and lay direction. The batch number is where any claim and any traceability starts; without it, later sampling has nothing to compare against.

List the documents precisely: material certificate, load table, test reports, installation instructions, maintenance manual, edge seal data and safety data sheets. Give a submission date for each rather than saying supplied with the goods.

Over-specification and the order of clauses

Over-specification takes three forms: fixing the recipe, such as a named resin grade and catalyst brand; fixing process figures, such as glass content to one decimal place; and fixing measures that do not matter, such as one exact Barcol value. None of them changes service performance, and all of them lock out suppliers and raise the price.

A better approach states the performance and the conditions and lets the supplier choose the route. Instead of requiring vinyl ester, write a design life of at least eight years in 20 percent sulphuric acid at 60 degrees Celsius, and ask for the immersion test report behind it.

The recommended order is duty, material family, geometry, load, safety, appearance, delivery. Each earlier clause sets the options for the later ones, and any other order produces contradictions.

For the full set of product parameters, compare the FRP grating specification guide

• Write span, load and environment before product data.
• Name the resin family, and the grade on important work.
• Put load and deflection on exactly one basis.
• Give a value and a method for every tolerance.
• State the performance and let the supplier choose the route.