The Art of Protection: Galvanised, Powder Coated & Painted Trailer Finishes Unpacked

Painting your trailer is essential to protect it from rust and corrosion, with the added benefit of improving its appearance. 

In this article, we unpack the three main types of trailer finishes:

• Galvanised
• Powder coated, and 
• Painted 

We examine each finish in detail, including the preparation process, pros and cons, and cost. 

Galvanised trailers

Galvanised steel refers to the treatment method used to extend longevity and enable the steel to withstand harsh environments. Galvanising is considered a sacrificial protection – the zinc coating absorbs corrosive materials before they can react with the steel. 

The galvanising process

This process involves the following steps:

• Surface preparation: Steel is thoroughly cleaned to remove dirt and contaminants. This is usually achieved through sandblasting or chemical washes.
• Immersion: 
  • Method #1: The trailer is fully submerged into a molten zinc bath at high temperatures allowing the zinc to chemically bond to the steel. This method is relatively quick and creates long-lasting protection.
  • Method #2: Electro-galvanising involves submersing the steel in a zinc solution and using electrolysis to create the zinc coating. Temperatures are much lower in this method, but the process does take a lot longer and leaves a thinner layer of zinc. The benefits of electro-galvanising is that it gives a more even distribution of zinc coating and a shinier surface. 
• Alloy formation: Upon removal from the zinc bath, excess zinc is drained off the trailer, leaving behind a solidified steel/zinc alloy coating. 
• Inspection and finishing: Trailers are usually inspected to check the coating thickness, adherence and uniformity. Minor touch ups for excess zinc and imperfections may be applied. 

NOTE: It is important that all section stock (RHS, SHS, etc.) and plate that is fully welded around the perimeter, has sufficient holes drilled to; A) prevent explosion from pressure build up and, B) to allow the excess zinc to drain. For detailed instructions, contact the dipping facility prior to starting your build as the location of the holes may affect how you put your trailer together. Be aware when drilling the drain holes as you do not want to affect the integrity of the trailer.  

The cost of galvanising

In terms of cost, galvanising ranges between $3 – $5 AUD per kilogram of steel. Keep in mind that you are charged per kilogram after the dipping process, which generally adds an extra 4% to the total mass.

Example: Flat Top Hydraulic Tipping Trailer
Total weight of steel	300kg
Weight after dipping	300kg x 1.04 = 312kg
Average price per kg	$4.00
Cost of gal dipping	$312 x 4 = $1,248.00

An alternate solution to hot dip galvanising is to build your trailer from pre-galvanised steel. This is a cheaper option and can save you time as you won’t be waiting on the galvanising facility (if you even have one in your locality). Once you have built the trailer you can treat the welds with a zinc-based paint. In my experience, this works well on the farm but is not a great option if you are trying to mitigate against saltwater. Often the painted welds will start to rust within 12 months. 

Galvanising pros and cons

Pros	Cons
Hard smooth coating resulting in a scratch resistant finish.	Higher cost.
Low maintenance.	Not all trailer parts can be galvanised – depends on their size, shape and material.
Durable and long-lasting; 20+ years.	Lacks the colour and finish options achieved with powder coating or painting.
Rust and corrosion resistant.	Requires drilling drain holes.

Galvanising is typically the best option for boat trailers where superior rust protection is required.

Powder coated trailers

Powder coating involves applying an electrostatically charged dry powder to clean steel. The charged powder particles seek to ground to the steel, and after heat treatment, form a hard finish. 

The powder coating process

This process involves the following steps:

• Surface preparation: Just like galvanising, a clean trailer frame is essential for the future durability of a powder coated trailer. 
• Powder application: Using an electrostatic spray gun, powder particles are positively charged and sprayed onto the negatively charged metal surface where they adhere to it. 
• Curing: Once the trailer has been completely coated, it is transferred to a curing oven where heat causes the powder particles to melt, flow together and chemically react. This ensures a durable, protective coating is formed. 
• Cooling and inspection

The cost of powder coating

In terms of cost, it varies greatly depending on the provider. For a trailer similar to the one mentioned in the above example, you could expect to pay between $1,800 – $2,300 AUD.  

Powder coating pros and cons

Pros	Cons
Aesthetically pleasing finish.	Highest cost of all the paint coating options.
Smooth hard finish (scratch resistant, but not as good as galvanising).	Not something the home DIYer can easily achieve.
Various colour and texture options.	Often length waiting time on provide
No product running or dripping – it’s a ‘dry’ product.
Gets into difficult to reach places.

Paint coated trailers: the DIY project

Traditional DIY paint coatings are still widely used for trailers. The best paint for a trailer will be heavy duty epoxy-based paint, but don’t forget the preparation and primer first!

The painting process

This process involves the following steps:

• Surface preparation: You’ll need gloves, eye protection and a suitable respirator – paint fumes and sanding dust are NOT good for you! Ensure your trailer is in an elevated position. This allows you to easily reach the underside. First, you need to thoroughly sand and clean your trailer to remove dirt and contaminants to ensure optimal adhesion of paint. Once you’ve sanded the trailer, make sure you remove any dust with an air compressor and wipe the trailer down with a cleaning solvent, such as acetone to remove residue. Note: remove any welding spatter before painting – no one likes seeing welding spatter on a completed project!
• Primer: The primer acts as a bonding agent to enhance paint adhesion and improve the durability of the coating. You will need to choose the correct primer. For clean shinny metals like Aluminium, galvanised or untreated steel you will want and etch primer, if you are painting over existing paint (must have existing solid adhesion, no flaking) for example pre-primed steel ‘blue’, you will want an all-purpose primer. Yes, it is primed but your joints aren’t and there will be scratches and burns throughout the build process. Prime again! 
• Topcoat: After the primer has dried it is time to apply the topcoat’s. Multiple coats, typically 2-3, are required to ensure good durability – be sure to respect the required paint drying times between each coat! 
• Curing and drying: After the final coat has been applied, it’s important to allow the paint to properly dry and cure. This allows the paint to harden and form a protective layer. Drying times will vary for each different paint product. From my experience this can take a week or so even in warm weather.  

The cost of painting

In terms of cost, many people believe this is the cheapest option. It is…just!

But what lifespan do you want out of your trailer? When you consider the time involved to achieve a finish with a similar lifespan to either gal dipping or powder coating, the cost is actually higher. This is because of the necessity to re-coat your trailer every 5-10 years, not to mention the time it takes to do this. 

To achieve a good quality DIY paint job for the Flat Top Hydraulic Tipping Trailer you are looking at between $500-$800 and even more if using a 2 part epoxy paint.  

Painting pros and cons

Pros	Cons
Aesthetic customisation – can paint different parts in different colours to suit branding.	Lower durability – prone to chipping and flaking.
Suitable for the DIYer.	Labour intensive.
Cheaper than other methods.	Re-coating required every 5-10 years.
Easily repairable.	Poor choice for boat trailers.

In summary

You should now have a pretty good overview of each trailer finish, and if we haven’t already communicated this enough, painting your trailer is crucial for safeguarding against rust and corrosion which will only give you headaches! 

Important tips

• Choose the coating to suit the environment it will be used in.
• Preparation is the key to having a surface treatment that lasts (this applies to all forms of coatings).
• Give it time. Painting takes time to get right – be patient.

frequently asked questions

Q: What paint should I use on a rusty trailer?

A: You should NEVER paint over a rusty trailer frame. Before giving your trailer a new lease of life, clean away rust and apply a rust proof agent to reduce further corrosion before following the steps above. 

Q: Can I powder coat a galvanised trailer?

A: Yes! We call this the duplex effect because it provides extra long-term protection. 

Q: What about stainless steel trailers? Can I paint them too?

A: We do not recommend painting a stainless steel trailer. This is because paint can reduce the corrosion resistance of stainless steel – stainless steel needs oxygen to repair its protective film.