Zinc Thermal Spray for Building and Construction

Last Updated 1 month ago by Kenya Engineer

Corrosion, the relentless enemy of steel, poses a significant threat to the longevity and safety of buildings and infrastructure. While traditional paints and coatings offer some protection, if one wants robust and long-lasting corrosion resistance, zinc thermal spray emerges as a superior solution.

What is Zinc Thermal Spray Technology.

Thermal zinc spraying is a process whereby a stream of molten zinc droplets impacts on the substrate( usually steel ) followed by flattening, rapid solidification and cooling processes. The individual molten Zn droplets spread to thin lamellae, the stacking of which constitutes the deposit. Thermally-sprayed coatings generally have a lamellar structure. The properties of a thermally sprayed coating depend on its microstructure which, in turn, depends on the spraying process used. The relationship between the properties and structure of a coating is of key importance in determining whether a desirable coating can be produced.

Surface Preparation: The steel substrate undergoes cleaning, removing dirt, rust, and any contaminants that could hinder adhesion and grit blasting to form a mechanical keying profile and roughness typically SA 2.5 or better still SA 3.0

Thermal Spray Process: The chosen zinc material, typically zinc wire or zinc powder, is fed into a thermal spray gun. The thermal spray gun generates the molten zinc spray by means of an electric arc or flame.

Molten Metal Deposition: The molten zinc particles are propelled at high velocity towards the prepared steel surface. Upon impact, they flatten and solidify, rapidly forming a dense and adherent zinc coating. They form lamellae on the surface.

Building the Layers: Multiple passes are applied to achieve the desired coating thickness, typically ranging from 50 to 250 micrometers.

The resulting zinc layer on the steel provides excellent corrosion protection:

Sacrificial Protection: Zinc in the thermal spray coating acts sacrificially. When exposed to moisture and oxygen, the zinc corrodes preferentially and provides protection to the underlying steel.
Barrier Effect: The zinc coating acts as a physical barrier, stopping the ingress of a corrosive environment and hindering the corrosion process.
Cathodic Protection: Zinc’s inherent electrochemical properties provides cathodic protection to the steel substrate and is consumed preferentially.

Advantages of Zinc Thermal Spray in Construction

Compared to traditional anti-corrosion coatings such as paints, zinc thermal spray offers several compelling advantages:

Superior Corrosion Resistance: Thermal spray coatings provide exceptional long-term protection, often exceeding the performance of paints and other coatings.
Durability and Longevity: The thermally applied zinc layer is highly resistant to mechanical wear, harsh weather conditions, and UV radiation.
Versatility: Zinc thermal spray can be applied to various steel structures, new or existing, including complex shapes and large surfaces and there is no curing time required
Thicker Coatings: Unlike paints with limited thickness capabilities, thermal spray allows for the application of thicker coatings, offering enhanced protection in highly corrosive environments.
Minimal Maintenance: Due to its exceptional durability, zinc thermal spray coatings require minimal maintenance. However, the application of an organic coating over zinc thermal spray makes for an excellent anti corrosion system.

Applications of Zinc Thermal Spray in Construction & Civil engineering

The exceptional protection offered by zinc thermal spray makes it a preferred choice for numerous applications in construction:

Structural Steelwork: This includes beams, columns, trusses, and other primary steel components that are crucial for the building’s structural integrity.
Secondary Steel Elements: Railings, staircases, support structures, and other secondary steel elements benefit from the long-lasting protection offered by zinc thermal spray.
Exposed Steelwork: Elements like fire escapes, architectural features, and exterior cladding exposed to harsh environmental conditions are prime candidates for zinc thermal spray.
Offshore Structures: Exposed to constant saltwater immersion, offshore platforms, piers, and other marine structures require the excellent protection offered by zinc thermal spray. However it is strongly recommended to overcoat with two further organic coatings to achieve excellent and long life protection in marine environments.
Rehabilitation and Repair: Zinc thermal spray is an excellent solution for restoring and protecting corroded steel surfaces. It can be used to repair existing damage or as a preventative measure on aging structures. If one cannot hot dip galvanize an existing steel structure, then zinc thermal spray is the answer.
Cathodic protection of concrete rebar: if a large square /rectangular area of a concrete bridge or structure is zinc thermally sprayed and connected to wiring that is connected to rebar in the concrete then the zinc thermal spray acts as a sacrificial anode and stops rebar corrosion

The key to successful Zinc Thermal Spray

To maximize the effectiveness of zinc thermal spray in construction and civil engineering, several key considerations come into play:

Surface Preparation: Thorough cleaning and surface profile creation are crucial for achieving optimal adhesion between the zinc coating and the steel substrate.
Zinc Material Selection: The choice between zinc wire or zinc powder depends on factors like desired coating thickness, surface roughness, and application efficiency.
Coating Thickness: The required thickness varies based on the level of corrosion protection needed and the specific application.
Environmental Conditions: Thermal spray application may be affected by factors like temperature, humidity, and wind. Choosing the appropriate weather conditions is crucial.
Safety Precautions: The thermal spray process involves high temperatures and molten metal. Follow good safety procedures, including proper ventilation and personal protective equipment is essential.

Compiled by: Simon Norton- Director IZA Africa Desk