FRP Grating Resin Selection Guide
The resin system determines how long the grating survives your environment — and roughly what share of the panel price it carries. Four systems cover essentially every industrial application. This guide puts them side by side and ends with a selection matrix by industry.
The four systems at a glance
| System | Corrosion resistance | Max continuous temp | Fire | Relative cost |
|---|---|---|---|---|
| Orthophthalic (ortho) | Mild — dry, neutral environments | ~60 °C | Standard | 1.0 (base) |
| Isophthalic (ISO) | Good — splash, fume, wastewater duty | ~80 °C | Standard / FR option | 1.15 |
| Vinyl ester | Excellent — strong acids, alkalis, solvents | ~100 °C | Class 1 option | 1.4 |
| Phenolic | Very good, acids favored | ~140 °C | Class 1, lowest smoke | 2.0 |
Orthophthalic — when it is actually fine
Ortho resin is the budget entry and is perfectly adequate for dry, non-corrosive interiors: warehouse mezzanines, electrical rooms, covered conveyor walkways. Its weakness is hydrolysis — continuous wetting, especially warm or acidic, breaks down the ester bonds over years. If the deck gets hosed, splashed or sees condensation, step up to ISO and the price difference is minor.
Isophthalic — the industrial default
ISO polyester is the correct default for the majority of industrial walkways: wastewater plants, food wash-down, general chemical splash, marine air. It handles continuous H₂S atmospheres and chloride splash, tolerates freeze-thaw wetting, and costs about 15 % over ortho. Choosing anything above ISO for a splash-zone walkway is usually over-specification; choosing ortho below it is under-specification.
Vinyl ester — buy it for the chemistry
Vinyl ester's epoxy-backbone chemistry resists hydrolysis, strong acids (to useful concentrations), alkalis and solvents that destroy polyesters. Typical cases where it is genuinely required: pickling and plating lines, chemical process areas, bleach plants, immersion or tidal-splash service, and hot acidic condensate. Retention data of about 95 % flexural strength after 12 months in 10 % sulfuric acid is the number that justifies the 40 % premium — twice.
Phenolic — buy it for fire and smoke
Phenolic's reason to exist is fire performance: Class 1 flame spread with the lowest smoke and toxicity of any FRP resin, which is why offshore escape routes, tunnels and naval applications specify it. Its corrosion resistance is good but its chemistry profile is narrower than vinyl ester (strong alkali is not its friend), and it is the most expensive system. Specify phenolic where the fire case demands it — not as a premium corrosion upgrade.
Selection matrix by industry
| Application | Default system | Step up when |
|---|---|---|
| Wastewater treatment | ISO polyester | Digestate or dosing areas → vinyl ester |
| Chemical process | Vinyl ester | Low-smoke requirement → phenolic |
| Marina / dock | ISO polyester | Permanent immersion → vinyl ester |
| Offshore | Phenolic | — |
| Food & beverage wash-down | ISO polyester | Hot acid or CIP chemicals → vinyl ester |
| Mining reagent areas | Vinyl ester | — |
| Dry interior mezzanine | Ortho | Any wetting at all → ISO |