ZINGA was originally invented at the University of Ghent (UGent), Belgium, in the 1970s and has since been used in a wide variety of projects throughout the world.
Cold Galvanizing for Steel
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 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 ZINGA has an unlimited pot-life and it doesn’t go “tacky” like a paint.
HOW DOES IT WORK?
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 the 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 galvanising (HDG) and zinc thermal spraying, both of which exhibit a constant sacrificial rate of the zinc layer.
With ZINGA the sacrificial rate reduces dramatically after the zinc layer has oxidised and the natural porosity has been filled with zinc salts. Additionally the zinc particles within the ZINGA layer are protected by the organic binder without adversely affecting the electrical conductivity. This enables ZINGA to create nearly the same galvanic potential between the zinc and the steel as hot dip galvanising but with a lower rate of zinc loss because, put simply, the binder acts as a “corrosion inhibitor” to the zinc.
Extract from B.N.F. Fulmer report of JJB Ward, Oxfordshire, Jan ’92
The zinc in Zinga becomes the sacrificial anode in relation to the steel but it corrodes at a much slower rate than would otherwise be expected
If the ZINGA layer is damaged to expose the base metal below, the steel would form a layer of zinc corrosion products but no corrosion would take place beneath it. This is called “throw” or “throwing power” and enables ZINGA 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. 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 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 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, 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 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-oxidising. This layer of oxides is the reason behind the matt appearance of ZINGA as opposed to the shiny hot-dipped finish.
HOW IT CAN BE USED?
STAND ALONE SYSTEM
ZINGA provides comparable protection to conventional galvanising without the need for topcoats. Although ZINGA is only available in grey (the natural colour of zinc), the significant advantage of this form of application is that the 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 ZINGA).
ZINGA on its own is often used, because the structure is already on site or too big for the molten zinc baths. Additionally 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, ZINGA should be applied in two layers of 60 or 90 µm DFT each.
AS PRIMER IN A DUPLEX & TRIPLEX SYSTEM
ZINGA and the topcoats work in harmony to extend the lifetime of the system. As the ZINGA layer will not begin to sacrifice itself until the topcoat is breached, the original zinc thickness is maintained whilst affording the topcoat protection from under-creep and blistering.
In a duplex and triplex system (Active + Passive), ZINGA should be applied in 1 layer of min. 60 to 80 µm DFT.
For more information and application instructions, see ‘Overcoating ZINGA’.
AS SHOP PRIMER
At 30-40 µm DFT, 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 ZINGA is applied as a shop primer. The steel structure can be overcoated with ZINGA to obtain a cathodic protection or with any other paint without the need for reblasting!
Zinganised steel structures can be welded and bent during assembly.
REPAIR FOR WORN AND DAMAGED
This method is probably the most common use of ZINGA as it requires the simplest surface preparation. 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 ZINGA to the rough surface of the old galvanizing after appropriate decontamination of the surface and removal of the salts.
ZINGA is used globally in the construction industry on steel rebars prior to assembly and immersion as it delivers increased corrosion protection without compromising pull-out strength in even the lowest quality of concretes.
Independent laboratory testing performed by multiple institutes has proven ZINGA can guarantee twice the corrosion protection compared to that of galvanised or epoxy coated rebars.
CHARACTERISTICS - ADVANTAGES
EASY TO APPLY ONSITE
Once thoroughly mixed, ZINGA can be applied by using a normal paintbrush, a short-fibre roller (not for the first coat) or a conventional or airless spray-gun.
ZINGA can be applied in a wide variety of weather conditions. The application surface temperature range is from -15°C to +40°C where conditions allow with a maximum humidity of 95% so long as the dew point is 3°C minimum above the steel temperature. Like all coatings the substrate surface should be free from all types of contamination.
Working under ambient temperatures, ensures no deformation of the steel structure (which can happen in the hot dip galvanization process) or energy loss.
QUICK DRYING TIME
ZINGA has one of the fastest drying times in the coating industry. It is touch dry in around 10 minutes at 20°C (40 µm DFT). ZINGA can be recoated with a new layer of ZINGA 1 hour after touch dry (by pistol, after 2 hours by brush), and with other paints 6 to 24 hours after touch dry.
This benefit allows fast system applications, and consequently shorter application times, dry dock times (for ships), less man hours and shorter close down time of structures.
Since the cost of equipment, personnel and cost through economical loss due to non functioning of the structure is the highest of a coating project, this means ZINGA can be an immense cost saving.
ZINGA DOES NOT PEEL OFF AND IS NOT BRITTLE
ZINGA contains so much Zinc in its dry film, it does not form a closed film. In fact, ZINGA is porous. This is because the pigment volume concentration (for ZINGA = the concentration of Zinc), surpasses the critical pigment volume concentration of a coating.
This means that not every zinc particle is surrounded with binder completely, therefore allowing good contact between the zinc particles and consequently good electrical conductivity (which ensures cathodic protection).
Therefore, ZINGA is not a paint and does not behave like a paint. When a paint is damaged, it will cause a layer of paint to ‘chip off’ or ‘peel off’. Also when damaged with a hammer, a paint will suffer from the impact which causes severe stress on the binder of the paint causing the paint to show cracks. These cracks are the weak part of the paint through which moisture and water can seep leaving the steel exposed to the environment and rusting occurs.
ZINGA does not act like that, it acts more like the steel below: when impacted with a hammer, the Zinc is merely pushed away, bending along with the steel.
Therefore, ZINGA can also be bent with the steel to a certain extent.
One of the most decisive advantages of ZINGA is that it can be recharged. Each new layer of ZINGA makes the former layer liquid, so as to form a new homogenous ZINGA layer. There is no risk for accumulation of layers that are different in structure, which could cause peeling off. The surface preparation before recharging is reduced to a minimum: you only need to remove the Zinc salts of the surface. Depending on the age of the ZINGA layer, and environmental conditions, this can be performed with a water wash, preferably by steam-cleaning at 150 bar at 80°C or by sweep blasting (very light blast).
This property of recharging can be of use if you still have to do some drilling or welding on the surface, or if the structures still have to be transported. In that case the first layer is meant as a primer. It can intercept severe damages.
Afterwards the final layer of ZINGA can be applied and local damages can be repaired. The welding seams need to be cleaned beforehand. When there is no need to recoat the whole structure, you can apply a small quantity of ZINGA on the damaged spots and the whole structure is free from rust again. Repairs will be invisible after a certain time.
ZINGA CAN BE TOPCOATED
If ZINGA is used as part of a duplex system i.e. it is overcoated with a compatible paint system, the topcoat provides the initial barrier to the elements, but the zinc oxide will still form a secondary barrier if the outermost layer is compromised in any way. As the paint topcoat naturally begins to break down and becomes porous over time, the ZINGA fills the pores from below with zinc oxides enabling the top coat to last longer.
Additionally, ZINGA does not even start to sacrifice itself until the topcoat has become damaged to the point where it is exposing the bare zinc to the elements. It is because of this that we can state that the service-life of a duplex system can be 50% more than the sum of the individual lives of ZINGA and the paint topcoat when added together.
Always strictly adhere to the appropriate specifications provided by the topcoat manufacturers in conjunction with ZINGA. Although ZINGA can be easily overcoated with a wide range of topcoats, it should be noted that when using epoxies etc. that ZINGA is sensitive to solvents and all the necessary precautions should be taken to minimise its exposure to any solvents contained in the topcoats.
The use of the “mist-coat/full-coat” technique is vital and mandatory to prevent this from happening. For more information, please see “mist/full coat”.
Paint manufacturers will often specify a particular individual primer / topcoat systems, and these should always be applied over the correct tie-coat. Topcoats to avoid using in conjunction with ZINGA include all alkyd-based enamels, which must never be applied over any zinc based coatings. This is because the zinc reacts with the alkyd and causes saponification which allows the paint to dry but to never harden and cure.
High-build vinyls as well as acrylated and chlorinated-rubber enamels are extremely high in solvent content, so the use of a sealer is mandatory with these coatings.
Zingametall offers two sealers in its range, which have both been tested with ZINGA according to ISO 12944: Zingalufer and Zingaceram HS.
ZINGA is a unique coating product. Before application of any topcoat, a small test application should always be performed to see if any reactions occur.
FIRE RETARDANT PROPERTIES
A ZINGA unique system shows fire retardant properties. Moreover, it does not spread flames or produce toxic flames. This has been tested by two independent laboratories.
A fire test at SGS Yarsley Technical Service (UK) found that ZINGA has a class 0 surface (best ranking) in flame spread ranking.
A reaction to fire test was performed at Efectis (Netherlands) in 2013. ZINGA showed to propagation of the fire, no toxic smoke or droplets.
ZINGA is one of the few non specialized coatings that can be welded and applied over welds.
The welding of steel coated with ZINGA (max. 60 μm DFT) is possible without excessive zinc fumes because the heat of the approaching weld bead burns off the organic binder well below the melting point of zinc.
The remaining zinc dust is removed from the weld zone by convection leaving the weld-area free from contamination.
Another big advantage is the small ‘burn back’ from Zinganised steel that is welded. In epoxy paints, this can be tens of centimeters (to meters), with ZINGA this burn back is limited.
ZINGA can also be applied on welds without the needs of any special surface preparation (cleaning and roughening of the surface is necessary).
Once thoroughly mixed, ZINGA® can be applied by using a normal paintbrush, a short-fibre roller (not for the first coat) or a conventional or airless spray-gun. When applying ZINGA®, it must only be thinned with Zingasolv, which is available from your nearest distributor. Please read the appropriate Data Sheet.
ZINGA® can be applied in a wide variety of weather conditions. The application surface temperature range is from -15°C to +40°C, with a maximum humidity of 95% so long as the steel temperature is 3°C above dew point. Like all coatings the substrate surface should be free from all types of contamination.
The broad range of allowable application conditions that ZINGA® affords means that very few days are lost during projects due to poor weather i.e. the maintenance window is extended. This, combined with ZINGA®‘s unlimited shelf life, ensures minimal wastage of either time or materials during a project.
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