Galvanised and Dacromet Explained

Trailer and caravan parts are made in a variety of metals; aluminium, stainless steel and cast steel and iron. Cast steel and iron parts that need extra protection from salt corrosion are either hot galvanised or dacromet coated, both are Zinc coatings.

This guide explains where galvanised trailer wheels, galvanised trailer springs, galvanised trailer axle parts, galvanised trailer U-bolts and galvanised fish plates commonly fit into a trailer parts selection.

Dacromet and Zinc-flake

Dacromet is a brand name with a patented "zinc flake" application. Sometimes this brand name is loosely used to describe Zinc rich coatings. Cold galvanising is another term. Dacromet layer is applied by zinc flakes in a cold dip and spin process, dried and heated into the product at about 300 degrees Celsius.

Zinc-flake coatings are used to protect parts - like disc rotors, leaf springs, drums, calipers, u-bolts and fasteners. It has high corrosion protection and it is suited for thin layer thicknesses or detailed surfaces for a high quality finish. Zinc-flake coatings are resistant to both acidic and basic chemicals.

Zinc-flake is often used where threads, machined areas or fine detail should not be covered by a thick coating.

Hot dipped Galvanising

Hot dipped galvanising has been around for a long time and is best known. The part is dipped into a molten zinc mixture at a temperature of about 460 degrees Celsius. As the zinc coating weathers in air, it forms protective compounds that help shield the steel. The finish may show a crystallisation pattern on the surface, called a spangle, but appearance can vary.

Hot dip galvanising covers the steel and seals it forming a strong material that stops corrosion and protects steel from the elements. The finish is not as attractive and thicker than zinc-flake. It is not suitable for parts with threads or fine detail due to its thickness.

For trailer parts, hot dipped galvanising is usually selected where a heavier protective coating is useful and fine-thread detail is less critical.

Galvanised vs Dacromet trailer parts 

Both finishes are zinc-based corrosion protection, but they are not the same finish.

If a part has moving, clamping or braking surfaces, match the finish to the product listing rather than choosing by coating name alone.

Choosing finishes for common trailer parts 

Use the finish as one part of the selection. Load rating, bearing type, stud pattern and axle size still need to match the trailer.

For wheels, check stud pattern, diameter, rim width, offset and tyre suitability before browsing trailer wheels.

For springs, match the spring style, eye or slipper configuration, rating and mounting points before choosing a galvanised or Dacromet finish.

For axles, confirm tip-to-tip length, face-to-face measurement, bearing turn and load rating before selecting from axles and stub axles.

For U-bolts and fish plates, match the axle shape, axle size, thread size and plate style before ordering U-bolts and fish plates. Replace clamping parts if the thread is damaged or badly corroded.

Are galvanised bolts rust proof? 

No. Galvanised bolts are corrosion resistant, not rust proof. Any zinc coating can be damaged by wear, stone chips, salt water or long-term weathering.

Once the coating is cut or worn through, exposed steel can corrode. Check bolts, fish plates and U-bolts during servicing.

If the thread, shank or clamping surface is damaged, replace the part with the correct size and rating.

For boat trailers or trailers exposed to salt water, rinse parts after use and inspect the coating before reusing clamping hardware.

Check coating damage again before long trips, especially around threads, clamps and wheel hardware.

Quick finish selection checks 

• Confirm the part type first: wheel, axle, spring, U-bolt, fish plate, rotor or caliper.
• Match dimensions, rating and trailer application before choosing by finish.
• Use hot dipped galvanised parts where a heavier coating suits the part shape.
• Use Dacromet or zinc-flake where a thinner finish suits threads or fitted surfaces.
• Inspect coatings during servicing. No coating removes the need for maintenance.

Disclaimer: The information provided in this article is for general guidance only and does not constitute professional mechanical advice. Trailer components should be installed and maintained in accordance with manufacturer specifications and Australian Design Rules (ADR). Always consult a qualified mechanic or trailer specialist for specific applications. Trailer Spares Direct accepts no liability for work carried out based on this information. Ensure your trailer is roadworthy and compliant with your state or territory's regulations before towing.

Still unsure which coating suits your trailer parts? Please call our friendly sales team on 07 3205 8846, email us or visit our store at 4 Leanne Crescent Lawnton.