Pre-Galv vs Hot Dip Galvanised Strut Channel
The difference between pre galvanised vs hot dip galvanised strut channel comes down to when the zinc is applied, and how much of it. Pre-galvanised (PG) channel is rolled from steel that was zinc-coated at the mill before forming, giving a thin, even coat of roughly 12–20 microns. Hot dip galvanised (HDG) channel is fully formed first, then dipped in molten zinc, which builds a much thicker coat of around 45–85 microns covering every cut edge and weld. PG is lighter, cleaner, and cost-effective for dry indoor use; HDG lasts far longer outdoors and in corrosive or coastal sites. The choice is really about environment, budget, and service life. Ashish International, with 25+ years of manufacturing behind it, supplies both finishes to international coating standards, so your strut channel matches the environment it will actually work in. Below, the two finishes are compared on coating, corrosion life, cost, and best use. The Two Finishes at a Glance The fastest way to see the difference is side by side. The table below sets out how the two galvanising methods compare on the points that matter most for a GI strut channel coating decision. Feature Pre-Galvanised (PG) Hot Dip Galvanised (HDG) When zinc is applied Before forming, at the mill After forming, dipped in molten zinc Typical coating ~12–20 microns (Z275 / G90) ~45–85 microns (ASTM A123) Cut edges & welds Bare, protected only by nearby zinc Fully coated Best environment Dry, indoor, mildly corrosive Outdoor, coastal, industrial Cost Lower Higher Finish look Smooth, bright Thicker, matte, slightly rough One number decides most of this galvanised channel comparison: coating thickness. HDG carries roughly three to four times the zinc of PG, and that extra zinc is what buys the extra corrosion life. Everything else follows from that single difference. How Each Coating Is Actually Made The two finishes are made in a completely different order, and that order explains all their strengths and weaknesses. Pre-galvanised — steel coil passes through molten zinc at the mill in a continuous line, then it is slit, roll-formed, punched, and cut into channel. The zinc goes on first, so any edge cut afterwards is left bare. Hot dip galvanised — the channel is fully fabricated first, then lowered into a molten zinc bath. The zinc bonds to every surface, edge, and weld at once, forming layered zinc-iron alloy plus a pure zinc outer skin. Because HDG coats the finished part, it seals the very spots PG leaves exposed. That gap in the process is the real reason the two finishes suit such different jobs. What Happens at the Cut Edges Cut edges are where the two finishes part ways most clearly, and it is the detail that catches out many first-time buyers. On PG channel, every punched slot and sheared end exposes bare steel, because the zinc was applied before those cuts were made. Zinc is sacrificial, so the coating around a small bare edge corrodes first and protects the steel for a time — which is why PG performs well in dry indoor air. But in damp, salty, or industrial conditions that sacrificial zinc is spent faster, and rust can creep from the edges. HDG has no such weak point, since the channel is dipped after cutting, so slots, ends, and welds all carry full zinc thickness. For any exposed or coastal run, that edge coverage is exactly why specifiers reach for HDG and keep pre-galvanised slotted channel to dry environments. How to Choose the Right Finish Picking between PG and HDG is a short decision once you weigh the run against its environment. Work through these in order: Assess the environment — indoor and dry points to PG; outdoor, humid, coastal, or chemical points to HDG. Set the service life — a support meant to last decades outdoors justifies the thicker HDG coat. Weigh the budget — PG costs less per metre, so it suits high-volume indoor runs where corrosion risk is low. Check the fittings — match the channel finish with similarly coated spring channel nuts and threaded rod so the weakest-coated part does not fail first. Confirm the standard — ask for the coating spec (Z275/G90 for PG, ASTM A123 for HDG) in writing. Nail step one and most of the decision is settled, because environment, not price, usually dictates which finish survives. The finish matched to the site is the cheapest insurance a support system can carry. Where Each Finish Fits Best on Site The right coating follows the application, and most MEP jobs fall cleanly into one camp or the other: Pre-galvanised — indoor cable trays, dry-area HVAC framing, ceiling grids, and general internal MEP support structures. Hot dip galvanised — rooftop plant, external pipe racks, car parks, tunnels, water treatment, and coastal sites. Stainless steel — where even HDG is not enough, a stainless steel channel in SS304 or SS316 handles the harshest chemical or marine exposure. Powder-coated — a powder-coated channel adds colour coding or a clean finish for data centres and visible installs. For heavy outdoor runs, the finish choice often pairs with a stronger section such as a back-to-back strut channel or a solar mounting structure. Pick the finish by application rather than habit, and a support stays corrosion-free for its full design life. Both Coatings, One Reliable Source Corrosion protection is only as good as the plant that applies it — and consistency at scale is what separates a reliable supplier. Across 25+ years, Ashish International has built out three units over 60,000 square feet, producing 350 tonnes of MEP support monthly to controlled coating specs, so a PG or HDG order matches its stated microns batch after batch. That consistency is why sourcing companies, stockists, and B2B contractors from the UK and Europe to the Middle-East and Africa buy from us, and why some clients have partnered with us for more than 20 years, several under NDA for their own designs. We coat to the same Z275, G90, and ASTM A123 standards global
