The Zincalume coated steel coating has been formulated to give a significantly longer service life than a galvanised coating. This is of particular value in New Zealand where the prevailing winds carry corrosive salt laden air many kilometres inland.
Zincalume coated steel is produced by a continuous hot dip process similar to that used to manufacture galvanised steel. While both Zincalume steel and galvanised steel products have a steel base, galvanised steel has a coating of 100% zinc, whereas Zincalume steel has an alloy coating of 43.5% zinc, 55% aluminium and 1.5% silicon.
The Zincalume alloy coating weight is 150g/m2 (AZ150) covering both sheet surfaces and the steel substrate grade is either G550 or G300.
The Zincalume steel product has an attractive finely spangled silvery matt appearance. Zincalume® steel is recommended for the manufacture of:
- roofing and flashings
- wall cladding
- gutters and downpipes
- steel house frames
- garage doors
- garden sheds
It is formable, weldable and readily accepts paint finishes.
Zincalume steel has superior long-term corrosion resistance in most atmospheric conditions. This is achieved through the combination of the sacrificial protection of the zinc and the barrier protection of the aluminium. Test sites from around the world over a period of twenty-five years have provided a wealth of information about comparative performance of galvanised and Zincalume steel products. Test sites are placed in many different environments, ranging from typical rural, to severe marine. Corrosion rates are determined by exposing samples of Zincalume steel and galvanised steel on standard test racks and regularly monitoring the coating performance over a number of years.
Though corrosion rates vary according to the severity of conditions, Zincalume steel coatings out-perform galvanised coatings in almost all environments. This is particularly true in marine environments where Zincalume steel will provide a significantly longer service life than galvanised steel.
Painting Zincalume Steel
Zincalume steel is readily paintable using good quality primers and water-based acrylic topcoats. Paint manufacturers’instructions should be followed. Dirt, grease and any loose materials must be cleaned off so the surface is clean and dry prior to the first coat being applied.
Compared to galvanised steel, Zincalume steel performs exceptionally well in areas not regularly washed by rainwater. However, as with any steel-based product, regular washing of areas not naturally rain-washed is essential to ensure that a satisfactory life is realised from the product.
Rainwater collected from roofs clad with products made from GalvsteelTM, Zincalume steel and Colorsteel prepainted steel, will comply with the provisions of NZBC G12.3.1, provided the water is not contaminated from other sources. The first 25mm of rainfall from a newly installed roof must be discarded before drinking water collection starts. Where a paint or paint system is applied to the roof, its suitability for the collection of drinking water must be established.
Protection at Cut Edges
At the cut edge, Zincalume steel provides similar protection to galvanised coatings. The zinc/aluminium alloy coating of Zincalume steel provides galvanic protection to bare steel exposed at cut edges and by deep scratches.
Surface passivation enhances the protection of the galvanised and Zincalume steel product during storage, forming, handling and fixing. A completely new passivation system has been developed for Zincalume steel which offers a technical advance over the Zincalume steel product manufactured in Australia prior to October 1993. It largely eliminates the need for roll-forming oils, offers improved wet stack corrosion resistance and generally makes the product more mark resistant during handling and fixing.
Handling and Storage
The normal storage care, site cleanliness and installation procedures used for Galvsteel products apply to Zincalume steel products.
Although passivation provides improved protection during storage, care should still be taken. If Zincalume steel becomes wet during storage, the product should be immediately separated, wiped with a clean cloth and placed in a position where it can completely air dry.
As with Galvsteel, Zincalume steel is suitable for all but the most severe forming operations. With Zincalume steel, the new passivation system acts as a dry lubricant and in most cases will eliminate the need for additional lubrication in most forming operations. Solvent-based lubricants must not be used.
Zincalume steel can be satisfactorily welded using the following techniques:
- GMA (Gas Metal-Arc, often called MIG)
- Resistance welding (spot or seam)
- MMA (Manual Metal-Arc)
When welding Zincalume steel, excessive weld currents must be avoided. With correct welding procedures, sufficient coating is normally left on the Zincalume steel sheet to protect the substrate from corrosion. Weld repair should be carried out by coating with a zinc-rich paint. Adequate ventilation must be provided even though the welding of Zincalume steel gives off fewer fumes than galvanised steel.
Joining and Sealing
Zincalume cannot be soldered. Join Zincalume steel in the same ways as recommended for Colorsteel prepainted steel products. Use a neutral cure silicone rubber sealant in conjunction with mechanical fasteners such as blind rivets. Care should be exercised in the choice of rivets. Aluminium rivets are recommended. Monel, stainless steel and carbon steel rivets must not be used.
Most fasteners complying with the corrosion requirements of Australian Standard AS3566 “Screws – Self-drilling for the building and construction industry”, are suitable for use with Zincalume steel.
- Stainless steel fasteners should not be used with Zincalume steel or Colorsteel ENDURA or MAXX products in any environment.
- Lead headed nails must not be used.
- Use only low carbon (<15%) non-conductive sealing washers.
Flashings and Accessories
Flashings and ridge capping should be manufactured from the same coating system as used for the main roof area to ensure equal durability. For Colorsteel ENDURA or MAXX and Zincalume steel products, extended ridge caps, soft zinc, or practices such as cutting and notching are recommended. Where penetration flashings are required, neoprene or silicone rubber, EPDM aluminium or soft zinc all give excellent performance.
Marking Zincalume Steel
Black lead pencils must never be used for marking Galvsteel, Zincalume steel or Colorsteel prepainted steel products. The carbon in the pencil promotes corrosion which will etch the surface, leaving a permanent mark. Use a pencil of any colour other than black.
Information To Help You Avoid Problems
In almost all applications, Zincalume steel will out-perform galvanised steel. There are, however, a small number of applications for which galvanised steel is more suitable. Zincalume steel must not be used for:
- Formwork in contact with wet concrete.
- Products to be embedded in concrete. However, where very small volumes of concrete are involved (e.g. splashes) which are able to cure quickly, there is little corrosive effect.
- Animal shelters where ammonia levels are constantly high.
- Fertiliser storage sheds and containers.
- Culverts, or where Zincalume steel material is buried in the ground.
- Water tanks.
- Highly alkaline environments (e.g. cement manufacture).
- Coolroom products.