Most people choosing a patio pick the colour first and never think about what is under the paint. That is fair enough: the colour is what you see every day. But the roof sheets, gutters, beams and flashings on a patio sit in the Queensland sun and storms for decades, and what lasts is decided by layers you cannot see.
Every patio, carport and roof we build uses genuine COLORBOND® steel made in Australia by BlueScope. Here is what that steel actually is, in plain terms, and how you can tell you are getting it.
Five layers, not one
BlueScope describes COLORBOND® steel as five layers bonded together on its paint line. From the inside out they are:
- The steel base. High-tensile steel made to the Australian standard AS 1397. Roof sheet is usually G550, a strong grade that lets a thin sheet span between purlins.
- The metallic coating. A thin alloy layer that protects the steel from corrosion. More on this below, because it changed in 2013.
- A pretreatment. A conversion layer that helps the paint grip the coating.
- A primer. Baked on, and made to resist corrosion where the topcoat is scratched or cut.
- The topcoat. An exterior-grade paint, baked on, which gives the colour and takes the sun.
The underside of the sheet gets its own backer coat. On an insulated panel or a ceiling, that is the face you look up at.
The coating changed in 2013
You will still see older articles say COLORBOND® steel sits on ZINCALUME® AZ150 steel. That was true of the previous generation. Since 2013, BlueScope has made COLORBOND® roofing and walling steel on an AM100 metallic coating with Activate® technology: an alloy of aluminium, zinc and magnesium. BlueScope says it spent many years developing it, and that the magnesium helps the coating protect cut edges and scratches better than the old alloy did.
The number after the letters is the coating mass in grams per square metre, across both faces. It only means something when you compare coatings of the same type. A heavier coating of a different alloy is not automatically better or worse, which is why BlueScope talks about coating type and mass together.
The paint and Thermatech®
The topcoat on standard COLORBOND® steel is a high-durability polyester. BlueScope’s technical datasheet lists the primer and topcoat together at a nominal 25 microns, and classes the paint system under AS/NZS 2728, the Australian standard for pre-painted steel.
Most colours in the range also have Thermatech® solar reflectance technology built into the paint. It reflects more of the sun’s heat than a plain paint of the same colour, which can help reduce roof temperature. On a patio that sits in the afternoon sun, that is worth having, and it is one reason the lighter colours stay noticeably cooler to sit under.
Made and tested in Australia
BlueScope makes COLORBOND® steel in Australia, to AS 1397 for the steel and AS/NZS 2728 for the paint. It also runs one of the longest outdoor test programmes for building steel anywhere. BlueScope says it has more than 12,000 test panels on exposure across Australia, from mild inland sites to severe marine and industrial ones, and that it has been testing and refining the product for over 60 years.
Laboratory tests, such as salt spray and UV cabinets, are useful, but they run for weeks. The Queensland sun and the sea breeze run for decades. BlueScope publishes results from panels left outdoors for ten years, including how much the colour changed and whether the paint flaked or peeled. Long-term outdoor results like that are what we trust when we tell a customer how a roof will look in fifteen years.
Grades for different sites
COLORBOND® steel is not a single product. BlueScope makes a standard grade for most homes, COLORBOND® Ultra steel for harsher coastal and industrial sites, and a stainless product for the most severe spots. Which one suits your patio depends on how far you are from breaking surf or calm salt water, and BlueScope publishes the distances. We cover that in our post on building near the coast.
How to tell it is genuine
A colour name on a quote does not tell you the brand of steel. Plenty of products are sold in colours with the same or similar names. To check you are getting genuine COLORBOND® steel:
- Ask your builder to write "COLORBOND® steel by BlueScope" on the quote and the contract, for the roof, gutters, beams, posts and flashings.
- Look for the brand printed on the underside of the sheets or on the packaging when the materials arrive.
- Ask how the BlueScope warranty will be registered for your job, and who registers it.
A good builder will not mind any of those questions. We are happy to show you the branding on site.
Why it matters on a patio
A patio roof has more unwashed areas than a house roof: the underside of gutters, the tops of beams, the gap under a flyover and the post bases. Those are the places where coatings work hardest. Steel that has been tested outdoors for decades, with clear published rules for where each grade suits, takes the guesswork out of it.
We chose to build with genuine COLORBOND® and BlueScope steel because we know exactly what it is, where it is made and who stands behind it. When we bring samples to the on-site quote, that is the steel you are looking at.
COLORBOND®, ZINCALUME®, Activate® and Thermatech® are registered trade marks of BlueScope Steel Limited.