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Home » Product & Planning Guide » Painting & Protection » Thermal Spray Metal Coating


The application of specialist technology is always welcome on the inland waterways.

Here we look at the long established industrial marine process of thermal spraying a zinc coating that is now available for our canal boats.

Pressure washing the total hull area
Masking up to ensure no blast media enters the boat cabin
Correct specification of grit blasting media is essential for proper surface preparation.
Accurate coat weight application and total surface coverage is a skilled task.
The finished surface before final coating. Due to the spraying of fine metal particles there will be some infill of existing pitting.
2 pack epoxy blacking being spray applied to give the ultimate long term protection system.
The finished result, good for many years to come.
Established Technology, New Application...
This established technology has been around for over a century. These coating solutions can be used to provide wear resistance, electrical conductivity and thermal protection but it is their proven track record in providing a corrosion resistant barrier that makes the technology particularly suitable for the marine environment.

These systems are extensively used in the offshore industry to protect oil platforms, steel superstructures and both internal and external surfaces of shipping vessels.
Moving ahead to the 21st Century and with the increase in pleasure boating on our inland waterways; it is an obvious technology to apply for prolonging the life of our pride and joy.

Why Canal Boats...?
It makes perfect sense when you consider that this process is simply a proven technology transfer of anti-corrosion coatings. We already accept the use of zinc anodes in the battle against galvanic corrosion, so why not coat the whole hull in a system that carries long term guarantees and offers real benefits that outweigh the cost of the process.

How it Works...
Rather than a cold paint or roller applied system, thermal spray technology uses a low power arc occurring between two electrically charged wires to atomise the wire and turn it into a spray stream. The wire is known as the feedstock and, in the case of inland fresh water systems, is made from zinc.

In effect, the process is very similar to that of arc welding where the welder briefly touches the electrode or welding rod against the work piece and then withdraws it to form a stable arc. In the case of thermal spraying, the arc is between the wire feedstock rather than the welding rod and work piece.

As a result of the non-contact arc this type of sprayed metal coating is very thermally efficient and little heat is transferred to the part being coated. This is of particular importance for coatings below the waterline where it is impossible to remove insulation and panelling from a fitted boat.

Suitable for All...
So, if you have ordered a new shell to DIY fit, you build shells commercially and want to add value for your customers, or you have an existing canal boat that you want to give the ultimate hull protection to, this process is available to all owners and shell builders alike.

The Full Process, from Grit Blasting...
In the case of a canal boat hull, the preparation consists of grit blasting with the correct grade of blast media following the usual pressure washing process.
Blasting is essential in order to provide a clean and keyed surface for the next stage of the process. Extreme care needs to be taken here that, if already applied, the upper painted surfaces of the boat are not damaged. To this end, sophisticated extraction and protection systems have been developed to ensure that only areas to be treated are prepared. Spraying the Metal...
The next stage consists of the metal spraying itself. Specialist application equipment has been developed specifically for our market and includes full protection for the operator.

For boats used solely on the inland waterways, the metal used is zinc. For craft used in brackish waters, alloys of zinc and aluminium are used, but our advice is to fully consult with your chosen specialist application company to work out what is best for your circumstances.

As we mentioned above, the metal is introduced into the application equipment in the form of wires which are electrically charged. The equipment uses a low power arc to atomise the metal, allowing it to be spray transferred onto the prepared steel hull.

...Which Requires Accurate Spraying...
Experienced operators will ensure an evenly distributed coat weight which is measured to ensure consistency of coating of around 1kg of zinc per sqm. An added benefit of a spray coating is that smaller pits and scrapes will be filled, resulting in a more aesthetically pleasing end result.

...Before Blacking.
Following the testing of the zinc coating to ensure adequate application, the hull is then blacked in the owners’ choice of final protection system. A popular choice for a final cold applied finish is the 2 pack epoxy system which offers added water and chemical resistance over the more traditional bitumen and tar based systems.

The big advantage is clear and is the fact that if raw steel is exposed via a lock or mooring “incident”, the zinc coating will provide galvanic protection and prevent the pitting we all too often encounter around and below the waterline.

Added Value
With the cost of even a basic sail away shell being what it is, this process adds life and value to your investment. Typically the process carries a 10 year anti-corrosion guarantee, which indicates much longer protection if you look after the hull.

For more information, contact the specialists in the replating section of our Products and Services Directory.
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