Steel rusts when it meets moisture and air. A zinc coating stops that by covering the steel and, where the coating is scratched, by corroding first so the steel underneath is spared. Pre-galvanised and hot dip galvanised steel both rely on zinc, but they are made in different ways and suit different places.
Pre-Galvanised Sheet
Pre-galvanised sheet is coated with zinc at the steel mill, in a continuous process, before it is cut and formed. It is the standard material for many cable trays, raceways and channels.
- Even, smooth surface and tight thickness control.
- Well suited to indoor, dry and sheltered locations.
- The cut edges, punched holes and weld areas are not coated after fabrication, so these spots have less protection.
Hot Dip Galvanising
In hot dip galvanising, the finished steel item is cleaned and dipped into a bath of molten zinc. The zinc bonds to the steel and coats every surface, including edges, corners and holes. Because the whole item is coated after fabrication, nothing is left bare.
- A heavier, more durable zinc coating than pre-galvanised sheet.
- Protects cut edges, welds and drilled holes.
- The usual choice for outdoor, exposed and corrosive environments.
- Common for structures, towers, gratings and fixings.
Which Should You Pick?
- Indoor, clean and dry: pre-galvanised sheet is usually enough and is the more economical option.
- Outdoor or exposed to rain, dust or humidity: choose hot dip galvanised.
- Coastal, industrial or chemical areas: hot dip galvanised, and talk to us about extra protection such as painting over the zinc.
- Where colour or appearance matters: powder coated or painted finishes are available.
Why In-House Galvanising Matters
We fabricate and hot dip galvanise in our own facility. That means the steel is fabricated first, then galvanised, then checked, all under one roof. It keeps lead times predictable and lets us make changes to your drawing without waiting on an outside plant.
How to Specify It
State the finish clearly in your drawing or bill of quantities, for example "hot dip galvanised" or "pre-galvanised", along with the site conditions. If you are not sure, send us the location and what the steel will carry, and we will advise.
