WHAT IS PURE ZINC COATING BY SEAGUARD FILM GALVANIZING SYSTEM?
The SEAUGUARD FILM GALVANIZING SYSTEM ® combines many advantages: an active or galvanic protection, a passive barrier protection and an easy application. In order to offer a galvanic protection, a zinc concentration of at least 92% has to be present in the dry extract. Having 96% of zinc in the dry film, Seaguard by Zinga certainly meets this condition. Seaguard by Zinga offers an excellent active and passive protection:
- The Zinc provides active, cathodic protection through galvanic sacrifice.
- The barrier, provided by both the zinc oxides and the binder ensures a passive protection.
In case of mechanical damages or in case of expansion and shrinking of the metal due to temperature variations, there will be no formation of rust whatsoever.
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Seaguard by Zinga is a one component zinc rich coating or Film Galvanizing System containing 96% zinc (dust) in its dry film. It is a metallic coating and not a paint. The purity of the zinc used, is so high that dry Seaguard by Zinga does not contain any toxic elements.
Seaguard by Zinga is a unique form of corrosion protection because it provides both Active and Passive protection in a form that's as easy to apply as a paint.
SEAGUARD FILM GALVANIZING SYSTEM’S Seaguard by Zinga was originally invented in Ghent University, Belgium, in the 1970's and has since been used in a wide variety of projects throughout the world.
Seaguard by Zinga is an active zinc performance coating which works in conjunction with the metal beneath whereas paints are only passive barriers. Regardless of how thick paints are applied, they remain as barriers. Once they are breached corrosion sets in immediately. Despite this significant difference Seaguard by Zinga is still often mistaken for a paint simply because it's liquid and comes in a tin. But there are other more subtle differences. For example it does not "skin over" in the tin because Seaguard by Zinga has an unlimited pot-life and it doesn't go "tacky" like a paint. Seaguard by Zinga layer (microscopically)
When two different metals come in contact with each other in presence of an electrolyte (e.g. water), they form a galvanic cell in which the lesser noble metal (e.g. Zn) corrodes in favour of more noble metal (e.g. steel). This electrochemical reaction is the base for the complex field that is cathodic protection.
Galvanic, Cathodic protection, or active protection, arises from zinc (the anode) sacrificing itself in favour of the base metal -steel (the cathode) with the resulting flow of electrons preventing steel corrosion. In this way the protection of the metal is guaranteed, even when the zinc layer is slightly damaged. Other well-established methods of cathodic protection include hot-dip galvanizing (HDG) and zinc thermal spraying both of which exhibits a constant sacrificial rate of the zinc layer.
With Seaguard by Zinga the sacrificial rate reduces dramatically after the zinc layer has oxidized and the natural porosity has been filled with zinc salts. Additionally, the zinc particles within the Seaguard by Zinga layer are protected by the organic binder without adversely affecting the electrical conductivity. This enables Seaguard by Zinga to create nearly the same galvanic potential between the zinc and the steel as hot dip galvanizing but with a lower rate of zinc loss because, put simply, the binder acts as a "corrosion inhibitor" to the zinc.
"The zinc in Seaguard by Zinga becomes the sacrificial anode in relation to the steel but it corrodes at a much slower rate than would otherwise be expected"
- Extract from B.N.F. Fulmer report of JJB Ward, Oxfordshire, Jan '92
If the Seaguard by Zinga layer is sufficiently damaged to expose the base metal below, the steel would form a layer of surface rust but no corrosion would take place beneath it. In other words; if the surface discolouration was removed, the steel below would not be pitted or eroded. This is called "throw" or “throwing power” and enables PURE ZINC COATING to protect bare metal up to 3 – 5 mm away from where the coating ends - slightly less than new HDG. Zinc sacrificial anodes used on the steel hulls of boats below the waterline work on the same principle to protect metal in the surrounding area. Seaguard by Zinga is simply a different form of these anodes and is therefore sometimes referred to as a liquid anode or sheet anode when used in immersed conditions.
The ability of zinc to provide galvanic protection is a function of its mass per given area. Dry Seaguard by Zinga contains a minimum of 96% medicinal quality zinc by weight, the particles of which are significantly smaller and purer than those found in normal "zinc rich" coatings. The Seaguard by Zinga particles’ small size and elliptical profile ensure maximum contact between both the individual particles and the substrate. This greater density of active zinc per given area combined with the good conductivity of the layer ensures that charge flows through every millimeter that has been coated and therefore provides excellent cathodic protection.
Passive protection, as provided by paints and cladding, creates a "barrier" between the steel substrate and the elements. Once this barrier is compromised then the moisture and atmospheric salts will be able to start corroding the steel beneath the damaged area. This corrosion will then begin to creep extensively beneath the coating.
With Seaguard by Zinga, the organic binder and the zinc oxide layer that forms on the surface create an impervious barrier by blocking the zinc's natural porosity with oxide particles. Unlike other passive coatings, once breached the zinc oxide layer simply renews itself by re-oxidizing. This layer of oxides is the reason behind the matt appearance of Seaguard by Zinga as opposed to the shiny hot-dipped finish.
As a Stand-alone system
Seaguard by Zinga provides comparable protection to conventional galvanizing without the need for topcoats. Although Seaguard by Zinga is only available in grey (the natural colour of zinc), the significant advantage of this form of application is that the Seaguard by Zinga layer can be re-coated at any point in the future with the bare minimum of preparation and without compromising the integrity of the coating (see Re-charging of Seaguard by Zinga). Seaguard by Zinga on its own is often used because the structure is already on site or too big for the molten zinc baths. Additionally, Seaguard by Zinga is commonly specified on delicate structures (wrought iron gates, sculptures) or when architectural demands require a higher standard of surface finish (no need to drill to de-gas, fettle).
For optimal protection,Seaguard by Zinga should be applied in two layers of 60 or 90 µm DFT each.
As primer in a duplex system
Not everybody likes the colour grey and with the additional protection of a compatible topcoat, the coating durability offered significantly increases. Seaguard by Zinga does not even have to start actively working until the topcoat has been compromised and with no underlying corrosion creep or rust bubbling, the topcoat itself inevitably lasts longer. In a duplex system (Active + Passive), Seaguard by Zinga should be applied in 1 layer of min. 60 to 80 µm DFT.
As shop primer:
At a thickness of 30-40 µm, Seaguard by Zinga can be used as a shop primer. The big benefit is found in the fact that the steel structures do not require reblasting before coating if Seaguard by Zinga is applied as a shop primer. The steel structure can be overcoated with Seaguard by Zinga to obtain a cathodic protection or with any other paint without the need for reblasting! Seaguard by Zinga applied steel structures can be welded and bent during assembly.
Repair for worn and damaged hot-dip galvanized or metal sprayed structures
This is probably the most common use of Seaguard by Zinga as it requires the simplest surface preparation. Seaguard by Zinga's mechanism of protection is so similar to conventional galvanizing that they work in complete unison, as they are merely different forms of zinc. Rather than replacing galvanized assets, structures can simply have their protection "re-charged" by applying Seaguard by Zinga to the rough surface of the old galvanizing after appropriate decontamination and removal of the salts.
Widely used in countries where the available concrete can be of less quality, Seaguard by Zinga the steel re-bars before assembly and immersion in concrete ensures vastly increased protection from corrosion without reducing the pull-out strength of the bars. Recent tests in three independent laboratories showed that Seaguard by Zinga had at least twice the corrosion protection of either galvanized or epoxy coated rebars.