Pre-Weathered Zinc

Natural (bright-rolled) zinc is shiny when new and takes years to develop its characteristic grey patina. Pre-weathered zinc, also called pre-patinated zinc, is factory treated so that its surface already resembles that weathered finish. It is used where architects want a uniform matte appearance immediately, for instance on facades, prominent roofs and repairs next to old zinc.

How it is made

Manufacturers start with standard mill-finish titanium-zinc and run it through a controlled chemical surface treatment line. One producer describes its process as phosphating. Different treatments produce lighter blue-grey or darker graphite-grey finishes. Factory-applied transparent tinted coatings in blue, red or green tones are a related option; these typically last up to about 30 years before reverting towards natural grey.

Properties

• The metal is zinc throughout, so cut and drilled edges weather to match without needing touch-up paint.
• The finish is UV stable and not prone to rust streaking.
• Installation, folding and soldering methods are broadly the same as for natural zinc, although surface treatments may affect soldering preparation.
• The same design rules apply: ventilation or underside protection against condensation, allowance for thermal movement, and care when folding in cold weather.

Weathering over time

Pre-weathering does not stop the natural patina from forming. Over years the treated surface blends into the normal zinc hydroxy-carbonate layer, which is self-healing when scratched.

Where it is used

Pre-weathered finishes are popular for renovation and infill work in historic European streets, where new zinc must sit next to roofs that are decades old, and on facades where uneven early weathering of bright zinc would be conspicuous. Natural zinc normally needs about 2 to 5 years outdoors to reach a similar grey, faster in polluted air.