Step and counter-flashing systems — aluminium

Capral Aluminium is Australia's largest domestic aluminium extrusion and sheet manufacturer. For roofing step flashing applications, Capral 5000-series aluminium sheet (typically 5005 or 5052 alloy) in 0.7mm or 0.9mm gauge is the standard specification. Mill-finish aluminium has an uncoated, naturally oxidised surface — it is not pre-painted from the factory like Colorbond. Mill-finish aluminium can be painted on site after forming to match the wall render colour, tile colour, or another specified finish. Painting must use a paint system compatible with aluminium — typically an etch primer followed by an acrylic topcoat. Do not apply paint directly to unprepared aluminium without the correct primer. Aluminium is lightweight relative to lead, corrosion resistant in most environments, and can be site-formed using a sheet metal folder in the same way as Colorbond. However, aluminium is not as malleable as lead and cannot be hand-dressed into complex curved or irregular profiles. For step and counter-flashing on standard masonry wall abutments on tiled roofs, site-formed aluminium is a practical and cost-effective choice, particularly where a painted finish to match the wall colour is required. Dissimilar metal precautions apply — do not allow aluminium to come into direct contact with copper or copper-based products — use stainless steel fixings only.

Metalcorp is a major Australian steel and aluminium distribution business supplying sheet, coil, and section products to trade customers nationally. Metalcorp aluminium sheet in mill-finish and pre-painted finishes is used by roofing contractors and sheet metal fabricators for step and counter-flashing applications on pitched tiled roofs. Metalcorp supplies both mill-finish aluminium sheet (uncoated, natural oxide finish — paintable by contractor) and pre-painted aluminium sheet in a selected colour range. The pre-painted option can reduce on-site painting requirements where the pre-painted colour is close to the required match. Mill-finish Metalcorp aluminium sheet is specified for applications where the contractor will paint the formed flashings on site using an etch primer and acrylic topcoat. Metalcorp's aluminium product is available through their national branch network in standard sheet sizes and thicknesses suited to step flashing fabrication — typically 0.7mm or 0.9mm gauge. Forming method is the same as for Capral — site-formed with a sheet metal folder or supplied pre-formed by a fabricator. Fixings must be stainless steel — same dissimilar metal precautions apply as for all aluminium flashing applications.

Custom aluminium step and counter-flashing is specified when the standard profiles available from Capral or Metalcorp do not suit the application — for example, where an unusual tile profile, non-standard wall geometry, or an architect-specified custom profile is required. In this case, the contractor engages a specialist sheet metal fabricator who manufactures the step and counter-flashing to a drawn profile and specified aluminium alloy and gauge. The fabricator typically sources aluminium sheet from Capral or Metalcorp and forms, cuts, and folds the flashings to the required profile. Custom fabricator-supplied aluminium flashings can be finished in mill-finish (paintable on site), anodised, or powder-coated to a specified colour in the fabrication process. Powder coating in the fabrication process — before installation — provides the best colour durability and adhesion for colour-matched aluminium flashings. Specify: aluminium alloy (5005 or 5052), gauge (0.7mm or 0.9mm minimum for step flashings), profile (dimensioned drawing), and finish (mill-finish, anodised, or powder coat colour). Confirm the fabricator's lead time before programming the works. Use stainless steel fixings — same dissimilar metal precautions apply.