01All your galvanising & powder coating questions covered.

All of your galvanising questions covered.

Galvanising Guidelines

To ensure that your steel has the very best finish when galvanising, we highly advise reading our guidelines. Preparing your metal adequately beforehand will ensure efficient processing of your material.

How should I mark a job?

Use water soluble markers for steel marking, as this will prevent the need for additional cleaning.

What factors can influence coating thickness?

The following factors will make a difference in the thickness of galvanised coatings:

  • The quality of the materials you use plays a key role in the end result of your galvanised goods.
  • Elevated levels of phosphorus or silicon found in high-reactive steels can lead to excessive thicknesses.
  • Any metalwork already coated by the manufacturer (e.g., pre-lacquered or varnished) should be avoided and will require shot blasting beforehand.
  • Welding flux should be removed prior to delivery to LGPC, otherwise it will result in bare spots.
  • Over-pickling and pitting can occur where old or rusty steel is mixed together.
  • All metalwork must be fully shot-blasted prior to galvanisation.
  • Drainage and ventilation holes must be added to allow free flow of air and zinc, ensuring an even finish.
  • Tight moving assemblies, like hinges or sliding components, can freeze together during galvanisation. We advise galvanising assembly components separately then reassembling them after treatment.

What draining and venting is required?

This is an important requirement for any galvanising job.

Throughout the hot dip galvanising process, components will be fully submerged in pre-treatments baths and molten zinc in order to ensure all surfaces – internal and external – are treated. Any hollow structures like pipes, containers or beams welded around connection joins must have holes or cropping’s to allow any zinc or air to flow freely.

Ensuring the free flow of air and zinc is essential. Without adequate ventilation, there is the serious risk of metalwork exploding when immersed. This can cause untold damage to equipment, material and personnel.

If you are at all unsure what size holes are required or how much venting is needed, please contact us directly for further advice.

Venting & drainage guide for galvanising (MISSING FILE) Download

Are there any limits to the size of components which can be treated?

LGPC can cater for a broad range of component sizes. Call our team for further details.

Are there any component assembly recommendations?

Tight moving assemblies, such as hinges or sliding parts, can freeze together during treatment. As such, we recommend that the individual components should be galvanised individually and then assembled after treatment is complete. Where this is not possible, mobility within the assembly can be retained if the components are given an adequate clearance on each side.

Materials that vary significantly in sectional thickness, e.g., thin sheets attached to thicker frames, should not be galvanised together. The thinner material can warp in the zinc bath due to uneven heating.

Any metalwork already coated by the manufacturer (e.g., pre-lacquered, painted or varnished) should be avoided and will require shot blasting beforehand.

All welding residues should be removed prior to delivery to LGPC.

Galvanising Frequently Asked Questions

What is the best method of packing and transporting finished items?

In general, hot dip galvanised products should be transported in bundles or on pallets, ensuring they are not tightly packed together. This helps to prevent white rust from forming by allowing good airflow and reducing moisture. During winter, it is necessary to use covers to protect galvanised steel from the chlorides in road de-icing salts.

LGPC have an in-house logistics team that can arrange delivery of your finished items all across the UK using our fleet of low emission trucks. Get in touch for details.

Can materials warp during galvanisation?

Assemblies that contain steel with different sectional thicknesses (such as sheets in steel frames of heavier sections) can warp during treatment. Where possible, flat sheets that are less than 3-4mm in depth should be stiffened prior to galvanising.

Powder Coating Frequently Asked Questions

Where is powder coating used?

Chances are, no matter where you are in the world, you will be sat near a powder coated object. Whether it’s furniture, shelving, exercise equipment, railings, shutters or even a fire extinguisher, powder coating is used in a broad variety of applications for commercial products and construction.

We at LGPC powder coat a broad range of products including: Balconies, balustrades, railings, gates and architectural metalwork products.

LGPC stocks a wide range of RAL, BS and specialised colour ranges sourced from leading suppliers. Call our team at LGPC and let us help you with your project.

What are the difficulties powder coating on a galvanised substrate?

One of the main advantages of using LGPC for duplex coating your steel is that we are experts at both processes. If a supplier fails to understand one or both of these methods, it can cause significant issues in the quality of your finished product, especially as galvanised metal produces different reactions to being powder coated. Here is why it pays to have expertise in both areas.

Poor adhesion
Powder coating will offer good adhesion to standard metal surfaces provided they are fully degreased and free from dust and other contaminants. However, the quenching process of galvanisation can cause issues. Typically, galvanised steel is quenched in a weak sodium dichromate solution to prevent oxidisation and make the metalwork cool enough to handle. This solution applies a passivation film to the surface which can result in a complete breakdown of any powder coating adhesion, detaching it from the surface often in a dramatic way. Furthermore, such permeation will promote corrosion of the metal, accelerating the process. It is essential to use a supplier who understands and knows how to avoid these issues.

The predominant reason for pinholing lies within the substrate itself. During the hot dip galvanising process, gasses can get trapped within the metal skin and then during the curing of the powder coating, the trapped gasses start to escape through the paint film. This is how pinholing occurs. However, this should not be a catalyst for rejection. It is recognised within BS6497 that this can be a problem and is regarded as being acceptable if not excessive.

The chemical composition of some powder coatings may cause varied reactions when applied to a galvanised surface. In fact, some powder coatings containing polyesters are highly unsuitable for use over galvanised steel because of their tendency to create pinholes.

This is why any powder coatings for use on galvanised metal must contain anti-gassing agents. These agents are unable to completely prevent pinholing but will minimise its effects.

Differences in gloss levels will also create a different finish. Matt finishes are generally preferred as they reduce the visibility of imperfections. When specifying colours, please consult our team to see if the requested powder is available in the appropriate grade.

White rust
During storage or shipment, a white film (known as white rust) may sometimes occur on the surface. This occurs on newly galvanised steel when it comes into contact with condensate or rainwater and the moisture does not dry quickly. White rust is common in areas such as crevices between closely packed sheets where moisture can collect.

When zinc corrodes in the open air, it creates zinc hydroxide and zinc oxide, which transform into zinc carbonate when exposed to atmospheric carbon dioxide. Surfaces that have formed a normal protective layer of zinc carbonate are rarely affected. However, where air supply is restricted around zinc surfaces, sufficient carbon dioxide is not supplied for the normal formation of zinc carbonate.

The layer of zinc oxide and zinc hydroxide is voluminous, porous and only adheres loosely to the surface. This means it does not provide protection against oxygen in the water, causing further corrosion. Objects with white rust should be positioned so that their surfaces can dry rapidly and allow a free supply of air around all exposed surfaces to allow a normal protective layer of zinc carbonate to form.

How can you prevent white rust forming?

(Also see Galvanising FAQs)

White rust can be prevented from forming by ensuring good air flow around components during transportation. This allows rainwater and condensate to drain off and evaporate, keeping the galvanised surface dry. Any galvanised materials stored outside should be stacked so that water can run off and all surfaces are given adequate ventilation. Painting after galvanising can also offer additional protection.

Why specify EN13438: 2013?

Specifying EN13438:2013 gives you the peace of mind that your products are powder coated to the highest industry standards delivering durability and corrosion protection.

Why choose an Approved Applicator?

By specifying an approved applicator gives you third party peace of mind that LGPC is consistently meeting the highest industry standards in application.

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