Surface treatments and finishes

As with most materials, surface preparation is important before applying a finish. Oil and grease need to be removed before painting, and dents and scratches need to be filled and rubbed down with emery cloth or silicon carbide paper.

Once the surface is smooth the painting process can start, very much like painting timber:

  1. a basecoat or primer is applied first, which will show blemishes that would only stand out more with paint
  2. rubbing down again before painting is important
  3. once the primer coat is perfect, a layer of paint can be brushed or sprayed on
  4. layers can be built up until the colour is even
  5. a final lacquer coat can be added so that the paint is protected, and the final finish is shiny
Metal apparatus around a playground have been painted in bright colours.
Painted playground equipment

Dip coating is a popular finish for the handles of many tools and coat hooks. It is a straightforward process:

  1. a piece of metal is heated up to around 250°C
  2. once hot, it is then dipped into a polythene in powder form
  3. this has air blown through it so an even coating of the powder is dusted onto the hot metal, resulting in a smooth and shiny coating on the dipped metal

Polythene is available in many colours and can help improve grip when applied to tool handles.

Powder coating is a method of attracting paint in a powder form towards an electrically charged object:

  1. paint that is in powder form is sprayed from a paint gun
  2. the paint is attracted to the electrically charged object
  3. a fine and even coat of powdered paint covers the surface of the product and, once heated, the powder melts and produces a ‘run free’ paint finish
A metal car wheel rim is suspended from a bar while a hand powder coats it white.
Powder coating

Some metal products that are made from steel, such as watering cans and lamp posts, would rust if they were not protected. A common process that is used to protect such products is galvanising. Steel products are given a zinc coating by dipping them into the molten zinc. For example, corrugated steel roofs of farm buildings and sheds are often made from steel that has been galvanised. After a few decades, the galvanised coating will wear because of acid in the rain and the steel will start to rust, so the roof will need replacing one day.

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