Unistrut is the grown-up version of the Erector Set of our youth. Our Erector Sets gave us an endless number of possibilities to design, create and build. The Unistrut System works in much the same way, offering a wide range of mounting options, hole patterns, profile configurations, materials, and finishes needed to ensure project success. Material selection is an important step in the specification process, and we offer a wide range of application-specific choices based on material alone. When we combine a basic material selection (such as carbon steel) with our available finish options, the total number of available permutations increases exponentially. This post takes a closer look at Unistrut finish options and offers guidance on choosing the right channel and fittings for your project.
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Plain (PL)
Plain Unistrut means that the channel retains the oiled surface applied to the raw steel during the rolling process. Fittings with the PL finish will carry the original oiled surface of the bar stock material. If your application requires welding, Plain Unistrut is often a good choice because it does not require extensive surface preparation.
Perma-Green III (GR)
Unistrut’s perma-Green III finish provides superior resistance to chalking, checking, and fading. The Perma-Green finish is also less vulnerable to common acidic atmospheres, solvents, and alkalis. Unlike many competitive paint-based finishes, Perma-Green III contains no toxic metals. The Perma-Green finish offers more protection than Plain Unistrut Channel, but if you are looking for additional protection against corrosive elements, consider some of the options below.
Pregalvanized Zinc (PG)
Pregalvanized Unistrut is zinc coated during a hot dip process for added corrosion resistance. Steel strip from a coil is fed through a continuous zinc coater that cleans, fluxes and coats the steel with molten zinc. After cooling, the steel is recoiled. The PG zinc coating conforms to a G90 thickness designation per ASTM A653. The zinc thickness is .75 MIL or .45 oz./sq. ft. of surface area. This time-tested coating is good for indoor and outdoor applications. For more corrosive environments, the next step up in finish protection is our hot dip galvanized Unistrut channel and fittings.
Hot Dip Galvanized Unistrut (HG) ASTM A123 or A153
In hot-dip galvanizing, the finished part is immersed in a bath of molten zinc. This method produces complete zinc coverage and a thicker coating than pregalvanized or plated zinc. The zinc coating is typically 2.6 MIL or 1.5 oz./sq. ft. of surface area. For many years, the hot-dip galvanized finish was Unistrut’s most corrosion resistant finish.When contemplating using Unistrut with a zinc coating, it is important to remember correlation between service life and the thickness of the zinc coating as shown below.
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Unistrut Defender™ (DF)
Prior to the development of Unistrut Defender, specifying for highly corrosive applications meant choosing between galvanized finish or stainless material. Hot-Dip Galvanized Channel (HG) is significantly less expensive than stainless steel but more susceptible to corrosion. Unistrut’s Defender finish bridges the performance gap between galvanized and stainless, offering performance characteristics similar to stainless steel at less cost. Specifically designed for corrosive applications, Unistrut Defender utilizes two proprietary material coatings conforming to ASTM standards A1046 and A1059. According to independent lab testing, the end-result of this coating process is a finish three times more corrosion resistant than hot-dip galvanized products. If you are seeking improved performance over Hot-Dip Galvanized and balking at the price of stainless steel channel, Unistrut Defender provides an excellent mix of value and performance.
The electroplated galvanized steels have the pure zinc outer layer but lack the intermediate alloy layer that mixes the steel and zinc.
Galvanized surfaces will lose the spangle and form a gray zinc oxide film with a slight tooth or fuzziness to them. Sometimes, streaks of red rust will develop on galvanized steel surfaces where the steel is no longer getting the benefit of the galvanic protection.
One of the visual effects resulting from galvanization of steels is an appearance of crystalline spangling across the surface. The spangle is a unique and interesting formation on the galvanized surface. It is created by use of trace metals in the molten zinc, and by controlling the cooling process of the hot-dip zinc coating on the steel.
The process involves running a sheet, plate, structural shape, or constructed shape into a molten bath of high-purity zinc. Additional trace metals are put into the molten zinc to assist in the formation of the zinc crystal on the surface. As the hot, coated steel exits the bath of zinc, it is blasted with air to remove excess zinc from the surface. The zinc surface cools with the steel base material. As the surface cools, crystals of zinc develop across the surface.
Large spangles can be achieved on galvanized sheet, but it comes at a cost: these materials often contain lead content. There are other methods to create spangle on galvanized materials, including the use of Antimony, a lustrous grey metalloid for alloying metals. However, Antimony-alloyed galvanized steels are not typically of the same size as the lead-bearing galvanized steels.
Most manufacturers of galvanized sheet have ceased to produce galvanized steel with the high lead content required for a spangled appearance.
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