Galvanized vs. Galvanneal
Photos of the galvanizing and roll forming from other brochures will be inserted to the left.
The Nature of Steel Strut
G-Strut® and WIZcoat™ galvannealed strut are produced from steel that is designed to meet requirements for forming, drawing, bending, welding and painting - conforming to designations and test limits in accordance with provisions of ASTM A-653.
Gregory Framing Strut is produced from carbon steel that stands the test of time and high stress. Bare carbon steel, however, has one district disadvantage: it easily oxidizes or rusts.
The corrosion of steel is an 'electrochemical reaction' in which the steel, when exposed to oxygen via moisture, reacts to form an Iron Oxide alloy. The resulting 'red rust' combination of the iron and oxygen produces a non-protective surface that, over time, continues to react and actually dissolves the steel.
Options for protecting Carbon Steel Strut
Painting would appear to be a logical, aesthetic choice. Paint is a good 'barrier' or 'topical' coating that can shield the steel from the elements. Painting, however, has inherent weaknesses. Atmospheric exposure and breaches from general wear and tear will weaken paint's barrier and attack the metal. The resulting electrochemical reaction is so prolific that it will oxidize or 'eat' under and 'bubble up' the surface of the paint, a condition referred to as 'under-film' corrosion.
Zinc is an elemental metallic coating that, when bonded to steel, possesses the best of all worlds - barrier protection and galvanic protection. Galvanic protection is also an 'electrochemical reaction' whereby even the exposed steel is protected from corrosion. The zinc coating actually corrodes in the presence of moisture, rather than the underlying steel. The phenomenon is commonly referred to as galvanic corrosion, in which the zinc reacts as a sacrificial metal for the steel. The zinc is consumed during the long corrosion process at a rate 10 to 25 times slower than that of steel. Also unlike plain oxidized steel, oxidized zinc actually alloys and serves as its own barrier protection.
Gregory pre-galvanizes the steel that makes G-Strut® by quickly passing it through a molten zinc bath that binds the zinc into the surface of the steel. The result is a thicker, ductile layer of 'free' or pure zinc on the surface and a very thin alloy layer of zinc and iron - completing the 'circuit' for zinc's sacrificial metal property. The only real disadvantage is that galvanized product does not adhere paint very will unless pre-treated (and pre-treatment is general not cost-effective).
Hot-dipped Pre-galvanneal (WIZcoat™)
By subjecting the pre-galvanized strip to additional heat induction, the layer of 'free zinc' is effectively extended into an iron-zinc alloy all the way to the surface of the steel. The resulting product retains the desired 'galvanic protection' while gaining several new properties - most notably - paintability.
Galvanneal surface is dull, matted gray in appearance. Microscopically, the surface has cracks and crevices, which provide excellent paint adhesion without the need for pre-treatment (chemical etching, shot blasting). In salt spray tests, painted galvanneal strut actually outperforms conventional galvanized. Because strut is commonly spray painted post-installation, WIZcoat™ is the superior alternative. In contrast, when galvanized and pre-painted strut are spray painted post-installation, the resulting finishes are susceptible to peeling and cracking almost immediately.