Fiber-reinforced plastic (FRP) grating is a perfect substitute for steel and aluminum in corrosive or moisture-saturated conditions. It provides lightweight construction, high chemical resistance, and low-maintenance requirements.
But not every FRP grating does so. Molded and pultruded grating have very different structures, strength properties, and resistance behavior.
What is Molded Grating?
Molded grating is made by putting continuous fibers of glass in a mold and flooding them with resin to produce a one-piece, bidirectional panel. The process disperses the strength on both directions and gives square mesh openings of equal structural integrity.
What is Pultruded Grating?
Pultruded grating is made through a continuous process that involves dragging fiberglass rovings by a bath of resin and a heated die. This produces powerful, bi-directional bearing bars that are assembled into panels and provides high load-bearing capacities in the primary direction of the span.
Comparing Molded and Pultruded Grating
· Strength of the Structure
Molded grating has the same strength in each direction since the fiberglass reinforcement is applied throughout the panel in a woven form. Pultruded grating concentrates strength along the direction of the bearing bar, giving better span capacity but reduced cross directional loading support.
Also, molded grating is effective in irregular loading conditions, whereas pultruded grating is effective in long-span structural applications. The manufacturing process also defines performance attributes, mass distribution, and the way the structure behaves under stress to a large extent.
· Chemical Resistance
Thermoset resin systems including polyester, vinyl ester, and phenolic are used both in molded and in pultruded grating. Polyester offers cost-efficient chemical resistance. Vinyl ester provides a superior corrosion protection against acids and solvents. Phenolic resin enhances fire and smoke capability.
Molded grating tends to have more resin in it, which increases the corrosion resistance. Pultruded grating has greater aligned glass fiber, which enhances its strength, but by slightly decreasing surface exposure of the resin.
· Performance in Corrosive Environment
Molded grating works particularly well in harsh chemical environments because of the high proportion of resin to glass. The construction is solid and one-piece to reduce the exposed ends of the fibers. Pultruded grating also has high resistance to corrosion but can expose structural fibers at cut edges or bearing bars.
Molded grating is mostly used in chemical processing plants and wastewater facilities because of better corrosion resistance. Pultruded grating is used in environments with high structural loads and medium chemical exposure.
· Load Resistance
Molded grating distributes load equally in all directions. This bi-directional strength minimizes the local stress concentrations and is effective in situations with irregular loading pattern. It is applicable to platforms, walkways, and trenches with variable loads.
Pultruded grating provides much greater load-bearing capacity in the main direction of the bar. It covers greater distances between supports, decreasing structural framing considerations. This is perfect on the heavy equipment platforms and high walks.
When correctly oriented, pultruded grating exhibits reduced deflection under heavy linear loads. Similar stiffness performance may be achieved with closer spacing of the supports in molded grating
· Impact Resistance
The interwoven fiberglass construction of molded grating has the advantage of being able to absorb impact. Energy spreads out over the panel instead of being concentrated in one direction.
On the other hand, the pultruded grating has continuous fibers and are oriented in a single direction increasing strength along the axis but decreasing the dispersion of impact across the grain. The multi-directional reinforcement of molded grating enhances resilience in the dropped-object mode.
· Suitability for Heavy Traffic Areas
Molded grating is commonly used in areas with high tool drops or foot traffic with dynamic movements. On the other hand, pultruded grating is preferred with heavy industrial loads that possess predictable direction.
· Slip Resistance
Both types of grating have integrally molded or bonded gritted surfaces. Aluminum oxide grit enhances traction and minimizes the risk of slips.
Molded grating is frequently molded with built-in grit, which provides performance even with wear. Pultruded grating can have bonded grit surfaces. Both are also good in terms of slip resistance as compared to steel, particularly in wet or oily industrial conditions.
· Fire Resistance
FRP grating attains fire resistance with the resin formulation. Phenolic and specially designed polyester systems minimize flame propagation and self-extinguish in case the ignition source is eliminated.
Phenolic resin systems have less smoke density than the normal polyester. Molded grating tends to have good fire performance because the composition is rich in resin.
Molded and pultruded grating may be rated to both ASTM E84 flame spread and smoke development when produced with fire-retardant resin systems.
· UV Resistance
Continuous exposure to UV damages untreated surfaces of resin. The two types of gratings include UV inhibitors to prevent degradation.
To improve durability, manufacturers use surface veils and UV-stabilized resin additives. Molded grating generally has a longer surface integrity because of the resin coverage is thicker.
· Corrosion Resistance
Grating is exposed to salt sprays and humidity in marine and offshore settings. Molded grating works effectively due to its resin base that is resistant to corrosion. Pultruded grating is also resistant to corrosion but has the advantage of protective coating on exposed edges.
The ultimate durability will be dependent on the quality of resin and severity of exposure. Vinyl ester systems, when properly specified, provide very good longevity on both types.
· Moisture Resistance
FRP grating withstands water absorption in a much better manner than steel. The one-piece nature of molded grating eliminates internal routes of moisture. Properly sealed pultruded panels are highly waterproof.
· Temperature Tolerance
The two types have a wide temperature tolerance. Phenolic systems increase thermal stability and fire resistance. Only during extreme temperatures which exceed design limits, does structural performance deteriorate.
· Cost vs Resistance Trade-Off
Molded grating can also be cheaper in standard walkways and under heavy corrosion. Pultruded grating can be more expensive initially, but structural support needs less since the grating covers longer span. The extra investment may be justified by projects that require high structural strength and fewer supports.
Molded grating can be preferred in chemical-intensive environments to increase their corrosion resistance.
Comparing Molded Grating and Pultruded Grating Side by Side
| Resistance Type | Molded Grating | Pultruded Grating |
| Chemical | High resin content; excellent corrosion resistance | Strong chemical resistance; slightly lower resin ratio |
| Load | Bidirectional strength; moderate span | High unidirectional strength; long span capability |
| Impact | Superior energy distribution | Strong in bearing direction; less crosswise absorption |
| Fire | Strong with fire-retardant resin; good smoke control | Meets fire standards with proper resin formulation |
| UV | Thick resin surface improves durability | Requires UV additives and surface veil |
FAQs
What are the disadvantages of pultrusion?
Pultruded grating puts the concentration of strength in one direction, reducing crosswise load performance. Misalignment during installation lowers efficiency of structure. It is also possibly more expensive than molded alternatives in some applications.
Is molded grating stronger in both directions?
Yes. The interwoven fiberglass structure of molded grating offers an almost equivalent strength in both directions. This bi-directional strength aids unpredictable loading conditions.
Is FRP grating fire resistant?
FRP grating could also be made to perform fire-retardant when composed using suitable resin systems including phenolic or modified polyester. It is resistant to the spread of flames and can comply with the set fire testing conditions.
Which is stronger between molded or pultruded grating?
Pultruded grating is typically stronger in the direction of its bearing bars and can carry longer spans. Molded grating offers relative strength in both directions and does well in corrosive conditions. The more powerful one relies on the direction of the loads and project needs.
Partner with Primefrp
Primefrp is a leading molded and pultruded grating manufacturer in China. We design and manufacture gratings that comply with the ASTM E84, ASTM D635, ASTM G154 and OSHA 1910.22 safety standards.
You can choose our standard molded and pultruded grating or choose custom designs. At Primefrp, our engineers will ensure you get the right construction material for your project – Get a quote now.
