How to Paint Galvanised Metal

Galvanised steel enquiries to Rawlins Paints often fall into 1 of 3 metal paint categories; those wanting to paint already galvanised steel, repairing damaged galvanising, and those wanting to paint mild steel to be galvanised.

For general painting of galvanised steel, clean and degrease with methylated spirit, lightly abraded and apply 2-3 coats as required of Bradite One Can Matt or Eggshell in the colour/finish of your choice (2,400+ colour options available). White salts on weathered galvanising must be removed during cleaning and degreasing. Light surface rusting can be treated with Flag Rust Converter. Heavy rusting to be removed to clean metallic finish (SIS-St 3). For professional use, apply Kolorbond K2 as per its application instructions.

What Is Galvanised Steel?

Galvanised steel is a clean steel with zinc metallurgically bonded to the surface, completely covering the steel with a protective coating and giving a spangled appearance. This protects the underlying steel from abrasion and exposure to atmospheric conditions (such as acid rain) for many years, preventing rust that would weaken the structure.

How Is Steel Galvanised?

Hot dip galvanising is where steel components, large and small, are immersed in a vat of molten zinc heated to around 450°C. This forms a strong bond between the steel and the zinc on exteriors, interiors, and hard-to-reach places on immersed structures, with corners and sharp edges seeing a build-up of zinc coating where paints would usually thin. By coating interior and exteriors, structures made from galvanised steel won’t corrode from the inside outwards.

Some steels may not be able to be hot-dip galvanised due to their size, weight, or configuration. It could also be that the steel is already in situ and installed on-site. Although galvanising plants have quick turnarounds and the hot-dip process is relatively quick, deadlines can be missed with steels arriving for construction without galvanising. For these instances we supply cold galvanising paints, and zinc-rich primers for use under intermediate coats and topcoats on mild steel that is not galvanised.

Why Should Steel Be Galvanised?

There are many reasons why galvanised steel is preferred on construction sites by architects, specifiers, and engineers:

Durable and Tough

The durability of galvanised steel provides excellent corrosion protection, one of the best currently available on the market. It provides up to 10 times the abrasion resistance of organic paint coatings and has superior resistance to mechanical damage. Being highly chip resistant, this makes galvanised steel easier to handle, store, transport, and erect on site, helping to prevent damage during construction.

For times when galvanised steel takes a hefty knock on or off-site, Rawlins Paints have cold galvanising coatings for repairs to damaged galvanising.

Galvanising provides prevention of “sideways creep”, a kind of corrosion that can break down paint coatings from underneath, caused by rust deposits accumulating on the steel from damaged and exposed steel.

Cost-Effective

Galvanised steel structures require little maintenance than steels that lack protective coatings. The zinc coating itself is self-healing and reseals over light damage.

However, the up-front cost of galvanising is expensive on smaller projects. Rawlins Paints stock zinc-rich primers that are very cost-effective for use on mild steel, that can then be coated with intermediate products and topcoats in 4,200+ colours. We also have cold galvanising paints available.

 

Where Is Galvanised Steel Used?

Give its long lifespan, durability, and superior protection against corrosion and atmospheric elements, galvanised steel is favoured by architects, engineers, and contractors around the world for use in construction:

• Bridges – for vehicles and pedestrians
• Structural steelwork
  • Homes and apartments, including beach front properties
  • Offices
  • Industrial units, such as distilleries
  • Stadiums – main stand at King Power stadium Leicester City Football Club, Aviva Stadium in Dublin
  • Leisure centres
  • Car parks
  • Phone signal masts
• Facades
• Gates
• Walkways, ladders, staircases
• Fencing, chain links
• Guttering
• Balconies, verandas
• Sculptures
• Agriculture
• Railways
  • Stations
  • Maintenance buildings
  • Signal gantries
• Industry
  • Refineries
  • Power plants
  • Wind and solar farms
  • Mining equipment

 

Structures such as car parks are left open to the elements whilst providing shelter for vehicles and pedestrians. Galvanised steel proved to be an excellent material for use in construction due to its strength and durability, resulting in wider spans for more parking and walking areas, and little maintenance for decades.

Galvanising is also increasingly used in agricultural buildings due to its strength, long protection period, and being hygienic for use around animals. This is vitally important for when cows and other farm animals are sheltered in barns throughout winter.

Can You Paint Over Galvanised Steel?

Yes. Whilst galvanised steel has many benefits, many wish to paint it for aesthetics. This may help to blend in around other structures and existing buildings, particularly if used on an extension. Some areas may require high visibility colours to be used for safety reasons and regulations. Rawlins Paints stock a wide range of topcoats with 4,200+ colours for use on properly prepared and primed galvanised surfaces and mild steel.

Other reasons for painting galvanising may be to provide additional protection, particularly in aggressive environments such as offshore or coastal developments.

However, most paints will not be able to adhere to galvanised steel without the correct preparation of the substrate.

How To Paint Galvanised Steel

You don’t have to stick with the spangled appearance of galvanised steel. Rawlins Paints stock a wide range of coatings in 4,200+ colour options from RAL, NCS, and British Standard with which to paint over galvanising – but correct preparation must be adhered to.

Any paints to be used on galvanised steel surfaces should specifically state they are OK for use on galvanised steel in their product information produced by the manufacturer. Many paints are not OK to use over galvanised steel due to poor adhesion or reaction with the zinc on the surface. Preparation and cleaning is also absolute necessity before applying any coating but can be often rushed or skipped entirely due to the deceptively ‘clean’ appearance of new or weathered galvanised steel.

Pre-Treatments & Cleaners for Galvanised Steel

Galvanising must be cleaned thoroughly. Rust-Oleum Mathys ND14 Cleaner Degreaser is a great general use galvanising cleaner for consumers. It removes grease, oil, proteins, dirt, and many other surface contaminants from coated, mineral, and steel substrates. Very economical, 5 litres of concentrated ND14 will treat a surface of up to 500 m², based on a dilution of 1:20.

Our professional galvanised steel cleaners include Sherwin-Williams Degreaser W500 (formerly known as Envirogard W500), which can be applied manually or through use of a pressure washer.

More professional-use cleaners for galvanising can be found at our store.

Once cleaned and degreased you can prepare the surface for painting. There are below with the most common using T-Wash/Mordant Solution:

4. Blasting

Also known as “shot blasting” or “sweep blasting”, is often the preferred method of preparing galvanised metals such as steel. However, this is not always possible to do so; galvanising already installed or in situ may not be accessible, or smaller scale projects may not be cost-effective for blasting.

This mechanical method of preparation is favoured by professional users and removes a minimal amount of zinc oxide from the surface, ensuring it is slightly roughened to aid adhesion. Care and calculation need to be taken into consideration so not to damage the coating, especially on thicker coatings, hence why blasting is commonly left to professional use.

If you are able to prepare galvanising for painting by blasting, we would assume that the project is larger in size and/or requires more significant performance – if this is the case, you should contact our technical department so that we can discuss and recommend a suitable product or system appropriate to your requirements.

3. Weathering

Takes a considerable amount of time, often ruling it out from most construction projects. Leaving galvanised surfaces exposed for at least 6 months, ideally 12+, allows contaminants to be removed by rain, wind, UV light, and changes in temperature. You can then prepare with abrasive pads and brushes to remove loose and flaking materials before a hot wash with detergent. This should not, however, be considered where chloride levels are high, such as marine environments.

2. T-Wash and Mordant Solutions

Ideal for preparing galvanised steel surfaces for painting, especially where blasting is not an option and weathering would take too long. The process has been used for some time and is the best method to ensure adequate preparation has taken place. The surface will turn black or dark grey to indicate that the galvanised steel surface has been cleaned satisfactorily.

Very economical to use, T-Washing/Mordant Solutions are ideal for consumers and removes the need for specialist (and expensive) primers and paints as the surface will be suitably prepared.

Professional users may wish to skip this step if they cannot blast the surface. T-washing contains acids that attack the galvanised coating and applicators may prefer to suitably abrade galvanised steel themselves and then prime (see further below) or use a Direct To Metal paint.

Mordant/T-Washing consists of applying a phosphoric acid solution containing copper salts to the galvanised steel surface. Areas that have been satisfactorily cleaned will turn dark grey/black, helping identify those areas that which have not been satisfactorily cleaned prior to application of the Mordant/T-Wash. These areas must be re-cleaned and treated again.

This allows consumers and professional users to ensure the entire surface is uniform in colour for it to have been cleaned properly. It is a very effective method of preparation and leaves a roughened surface with a good key for paints to stick and adhere to.

Teamac Mordant Solution (T Wash) is an economical pre-treatment product for galvanising with coverage of up to 40m² per litre and is ideal for consumer use.

Rawlins Paints also stock professional pre-use treatments such as PPG Sigma Etch, used to help prepare galvanised steel for painting that cannot – or prefer not to – be mechanically blasted. For more professional pre-treatments for galvanising, see our online store.
Once the entire surface is uniform with our consumer or professional T-wash/Mordant Solutions, it should be rinsed down.

1. Primers

Help topcoats and intermediate coatings adhere to the surface of the galvanising. They can be used without T-Washing or Mordant Solution beforehand, but this means that the cleaning of the galvanising, and application of the primer, must be to an excellent standard.

Primers for Galvanised Steel

How to prep galvanized metal for paint

At Rawlins Paints we have a wide range of galvanised steel primers for consumer and professional use, suiting all needs. If there is something you cannot find or you require more advice on your requirements, feel free to leave a comment on this post at the bottom or contact our technical team directly.

Our consumer-based primers include Coo-Var Water Based All Metals Primer that can be used on interior galvanised surfaces as well as exteriors, by brush or roller. It is fast drying and can be overcoated with most paints.

Tikkurila Temaprime EE is a one-component anti-corrosive special primer for professional use on containers, agricultural machinery, and other steel structures. It adheres extremely well to different kinds of substrates, such as steel and zinc, drying fast for quick overcoating within an hour (at 20ºC).

Tikkurila Temaprime EE suffers minimum damage from burning, welding and flame cutting, ideal for use on construction sites. Burnt paint can be easily removed by brushing. Available in 1,000’s of colours!

Direct-To-Metal Paints

These paints can be applied direct to suitably prepared galvanised steel and left as a finish, answering the question “what paint will stick to galvanized metal?”

Zinsser Allcoat paints are very consumer friendly, requiring no primer when used on properly-prepared galvanised steel, and have a huge range of colours to choose from in over 4,200+ RAL, NCS, and British Standard shades. These include popular colours like Anthracite Grey and are designed for long term decoration of almost all substrates.

Rawlins Paints also stock a huge range of direct-to-metal paints for use by professionals only; this includes the Technispray Kolorbond K2 Set, a unique and durable lightfast two pack PU coating for direct application to galvanised steel.

Kolorbond K2 has many options to provide a truly bespoke painted finish for your galvanised steel. There are 2,400 colour options in RAL, NCS, and British Standard ranges to choose from, as well as the Steritouch range on request, and is supplied in smooth or textured with a matt, satin, semi-gloss, or gloss finish.

As long as the hardener and correct cleaner (Vinylkleen) and degreaser (Windowprep) are used, Kolorbond K2 has a 10 year guarantee on adhesion and 5 years guaranteed colour fastness.

Heat Resistant Paints

Where your galvanised steel surfaces require heat resistance such as in commercial and industry settings like factories, workshops, distilleries, etc, Jotun Solvalitt resists continuous temperatures of up to 600°C.

There is a choice of over 1,200+ colours for use on properly prepared galvanised steel and it can be used as primer, mid coat, or finish coat in atmospheric environments or as a heat resistant coating suitable for insulated and non-insulated surfaces in systems with suitable primers.

Cold Galvanising Paints

One of the more popular enquiries to Rawlins Paints is how to paint mild steel to make it look galvanised. This may be to repair damaged areas of already galvanised steel or to give non-galvanised sections of steel a galvanised appearance and similar protection.

As durable as galvanised steel is, accidents can and do happen on construction sites when erecting structures and installing steel into place – cuts, welds, drilling, knocks, and crane incidents are among those we’ve heard from customers. Galvanising can also be damaged well after installation by vehicles such as trucks and forklifts or struck by other materials.

‘Cold Galvanising’ paints such as those discussed in this blog can provide good protection and similar appearance to that of professionally hot dipped galvanised steel but should not be considered a like for like alternative to it.

 

Our zinc-rich Cold Galvanising paints can be applied to damaged galvanised steel for onsite and spot repairs. Our consumer-friendly cold galvanising options include Rust-Oleum Hard Hat 2185/1085 Galva Zinc, supplied in tins as well as a handy aerosol can.

Rust-Oleum are one of the world’s most recognised, renowned, and trusted brands in coatings, and with Hard Hat 2185/1085 Galva Zinc you’ll find a high zinc content coating that provides superior protection and durability for metals exposed to the elements or adverse artificial conditions. It can be used as a primer or as a single coat in light industrial exposures, corrosive environments, and high humidity areas.

We have more general use and consumer cold galvanising paints at our online store.

Zinga is a professional one-component anti-corrosion zinc coating system that provides cathodic protection to steel comparable with hot-dip galvanising, with the added advantage that it can be applied as though it were a paint and is certified to not spread flame or create smoke (BS476 parts 6&7).

The system can be used on marine structures, new steel and galvanising, old or worn galvanising as an alternative to hot-dip galvanisation or metallisation, as primer in a duplex system (active + passive) or as a recharging system for hot-dip galvanisation, metallisation or zinganised surfaces.

Click here to view Zinga at our online store, complete with data sheets. Be aware that some of our cold galvanised paints can be used for priming, prior to application with a topcoat if preferred.

Zinc Rich Primers for Mild Steel

We stock many professional-use zinc-rich primers that add protection to non-galvanised steel surfaces. These are used to provide a base for a system where similar protection to galvanising is required but hot dip galvanising cannot be carried out. Our primers are for overcoating with intermediate coats and topcoats in 1,000’s of colours.

Jotun Barrier is an excellent example of a zinc-rich epoxy coating for galvanised steel. Conforming to the compositional requirements of SSPC paint 20, level 2. Jotun Barrier provides very good corrosion protection as part of a complete coating system and is to be used as primer in atmospheric environments. Suitable for repair of damaged galvanised steel substrates, it complies with ASTM D520 type II zinc dust and more:

• Pre-qualification testing in accordance with NORSOK M-501, Rev. 5, System 1, suitable for exterior exposure in offshore environment, below 120°C
• Part of a complete system that is certified to Network Rail Line Specification NR/L3/CIV/039 – System M20 and N4 (Cert. No. XM92/M20-140 and XN90/N4-077) Item 7.1.3

This concludes our guide to painting galvanised steel – if you require help with your project, leave a comment below, or contact our technical team with your requirements.