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Pre-Weathered Steel Patina

façadeTek’s Pre-Weathered Steel Patina provides architects and designers with a range of colors on a long lasting surface. We produce this finish by accelerating the natural weathering process and developing the patina finish.

The Science

Weathering steel is a HSLA (high-strength, low-alloy) steel with improved atmospheric corrosion resistance. It is generally used for structures requiring extended longevity under low maintenance conditions. The product is produced to standards such as ASTM A242, A588, A606 Type 4 and A709. This product is commonly referred to as COR-TEN®, the original US Steel version. Alloys with small amounts of Cu, Cr, Ni, Si and P results in a steel that develops a stable rust layer that adheres to the base metal and is much less porous than rust which develops on carbon steel. The rust ‘patina’ develops under condition of alternate wetting and drying cycles to produce a protective barrier relatively impervious to further atmospheric corrosion. The appearance, texture and maturity of this coating depend on three interrelated factor: time, degree of exposure and atmospheric environment.

The façadeTek Automated Weathering Process – Rust/Oxidation

Weathering Steel, in its bare, mature state has a unique coating occasionally referred to as a “patina”. The coating is more properly referred to as a ‘protective oxide film’, which is about the same thickness as a heavy coat of paint. This protective oxide film adheres tightly to the weathering steel in fine, dense grains that are relatively impervious to further atmospheric corrosion, thereby sealing the base metal from the air and further corrosion.

All steels parts must be fabricated and welded prior to the patina process. Once parts fabricated, steel panels and shapes are treated to remove all mill scale, dirt, grease and other contaminants which allows for rapid weathering and uniform appearance. After this treatment, the steel undergoes a one-time shop applied treatment process to initialize the oxidation/patina process.

A proprietary solution is applied to the exposed steel and allowed to oxidize over several days. This process is accelerated by simulating greater misting and drying cycles during this period.

Once the initiation process is completed, the material is hung on our 30,000 square foot automated patina conveyor line that has two misting stations to simulate condensation cycles to accelerate the weathering process. The line runs 24 hours per day and 7 days per week till the protective coating that has been produced and will provide reduced run-off. This process results in the exposed steel having a relatively uniform rusty red-orange finish. Steel components are then removed from the line and shop assembled for field installation. Critical care must be used in the material handling as well as technical attachments. No water can be allowed to pond or develop on any surfaces. Once installed the steel continues to oxidize on the building to facilitate a mature protective oxidation layer.051

We cannot empirically say to what extent this will mitigate future runoff. It is the goal and expectation to develop the processes to accelerate the weathering and to provide the most analytical and details analysis of the weathering process along with necessary testing of surfaces.

Maintenance and Care

Surfaces of Weathering Steel which are wet for prolonged periods of time will corrode at a rapid rate. Minor damage to the oxide coating heals itself, with time the damaged area will match the surrounding areas. Implement an inspection program that recognizes the unique nature of uncoated weathering steel and the conditions resulting in excessive corrosion damage. Develop inspection guidelines that highlight the structural features to be inspected and also illustrate the difference between desired oxide coating and excessive rust scaling. Regularly remove all dirt, debris and other deposits that hold moisture and maintain a wet surface condition on the steel. Remove growth of nearby vegetation that prevents the natural drying of surfaces.


façadeTek will furnish project specific warranties.

Download Our Brochure

Download our Pre-Weathered Steel Patina brochure for more information.

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