Pultruded VS Molded Grating

‌Molded vs. Pultruded FRP Grating: Which One Deserves Your Project’s Crown?‌
By Peter Liu‌, FRP Solutions Engineer @CompositeWorks

Let me start with a confession: I used to hate pultruded grating. That changed in 2022 when a hurricane-flooded chemical plant in Louisiana proved me wrong. But we’ll get to that drama later – first, let’s dissect these two FRP giants like a curious engineer with a torque wrench.

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Molded Grating

Round 1: Manufacturing – Artistry vs. Precision‌

Molded Grating: Imagine baking a lasagna. Layers of chopped fiberglass strands (usually 60-70% glass content) get pressed into molds with polyester resin. The result? That iconic ‌crisscross diamond pattern‌ we’ve all tripped over at wastewater plants.

Pultruded Grating: Picture steel production’s nerdy cousin. Continuous fibers get pulled through resin baths (hence “pultrusion”), aligning like disciplined soldiers. This creates ‌unidirectional strength‌ – great for predictable loads, terrible for surprise side pressures.

Ah, but here’s the catch: Molded grating’s 25mm thickness often weighs 40% more than pultruded alternatives. I learned this the hard way when a rooftop bar project in Miami demanded last-minute weight cuts.

Pultruded FRP Grating

‌Round 2: Strength – Wrestler vs. Marathon Runner‌

Let’s break out 2024 ASTM tests:

Translation: Pultruded grating laughs at straight-line loads (perfect for bridge decks), while molded types handle chaotic impacts better (think forklift mayhem in warehouses).

Personal Anecdote Time: That Louisiana plant I mentioned? Pultruded grating survived 3 weeks submerged in saltwater – molded would’ve delaminated like wet cardboard. But when a drunk driver hit our pultruded security booth last month? Let’s just say we’re rebuilding with molded now.

‌Round 3: Chemical Resistance – Generalist vs. Specialist‌

Molded grating uses isophthalic resin as standard – decent against most acids (pH 3-11). Pultruded often relies on vinyl ester resin, making it a superstar in ‌pH 1-14 environments‌ (looking at you, battery factories).

Cost Reality Check: Want vinyl ester in molded? Prepare for 35% price hikes. Pultruded’s continuous fibers naturally suit premium resins.

‌Round 4: Installation – Weekend DIY vs. NASA Protocol‌

• Molded: Cut with circular saws (wear a mask – fiberglass dust is itchy!). My team once jury-rigged a section using zip ties during a monsoon. Held up for 8 months!
• Pultruded: Requires diamond blades and military-grade precision. Mess up the fiber alignment during cutting? You’ve just created a $2,000 noodle.

‌When to Choose Which?‌

‌Pick Molded If‌:

• Your site resembles a demolition derby (high impact risks)
• Budget’s tighter than a submarine door (15-20% cheaper upfront)
• You need curved sections (molded bends; pultruded snaps)

‌Go Pultruded When‌:

• Loads come from one direction (conveyor systems, mezzanines)
• Chemicals would melt steel (or your engineer’s patience)
• Weight savings trump all (helicopter-installed platforms, anyone?)

‌Final Thought‌:
I’m still haunted by the 3 AM call when molded grating in a Texas oil refinery sagged under unexpected heat. But then I remember pultruded’s glorious failure in that Chicago pedestrian bridge ice storm. Moral? There’s no “best” – only “best for right now.”

Got a project that keeps you up at night? Let’s geek out over coffee (black, two sugars – I’m only human).

About the Author:
Peter Liu‌ has engineered FRP solutions across 17 countries, from Arctic oil rigs to Bali eco-resorts. When not wrestling with resin ratios, he mentors young engineers and collects terrible puns. Reach him at info@fiberglass-profiles.com.