Stripping & Priming Metal

A surprising amount of metal is used in and around our homes – for central heating radiators, gates and railings, drainpipes and guttering and window frames. It seems odd, however, that metal, which is strong and hard-wearing, should be used in areas where it comes into contact with the one thing that causes it to corrode: water. Paint on its own won’t protect metal from rust, although it will slow down the rusting process. Inhibitors and primers are required to completely protect it from being affected by rust.

Where metal has been used in and around your home, check it routinely for rust. Look for telltale signs: blistering or flaking paint means water has penetrated. If you find any, set to work immediately. Scrape off the paint to expose every spot of rust. Light deposits can be removed using wire wool or wet-and-dry paper dipped in white spirit. Where the rust is heavy – i.e. where the surface of the metal has become ‘pitted’ – use a wire brush or wire wheel or cup brush attachment to a power tool. Next, paint a proprietary rust inhibitor onto the cleaned metal surface: always follow the manufacturer’s instructions as some inhibitors remain on the surface to protect the metal while others must be washed off after a few minutes. Wash grease off with white spirit and wire wool.

As soon as the metal is clean and dry, apply a primer. For general interior metalwork, use a red oxide primer. For exterior metalwork, use a red lead, zinc phosphate or calcium plumbate primer. Take extra care to work the primer into all the ‘nooks and crannies’ and pay particular attention to sharp edges and corners, which often get chipped and where corrosion can start.

Stripping Previously Painted Pieces

Most metal surfaces are painted or finished with an oil-based paint, which slows the process of corrosion. If existing paint on metal is sound, then a wash, rinse and dry is often all that’s needed to make it shine again. Sometimes, however, it’s better to strip away all the paint on metal and begin again from scratch, particularly on intricately moulded pieces where additional layers of paint will gradually clog up and obscure details.

If the metal piece is portable, you could get it professionally stripped by sandblasting or caustic dipping. The best DIY method to strip metal is with a chemical stripper. A hot-air stripper is of little use on metal – the metal simply gets hot before the paint itself actually gets soft. A gas blowtorch might work but you could easily end up cracking a piece of cast iron.

Once stripped, again apply a rust converter or inhibitor to remove or neutralize rust. Clean the stripped metal with a wire brush then wash with white spirit and prime the surface of the metalwork with a zinc phosphate or red oxide primer, working it well into moulded areas and corners.

Useful Tips

  • Before you chemically strip metal, make sure it really is metal. Some intricately moulded fireplace surrounds, for instance, may in fact be made of soft plasterwork on a wooden support.Tap the surround and listen carefully to the sound it makes, or scratch away a small area of paint to reveal the ground.
  • Enamelled finishes on metals (such as enamelled bathtubs or solid fuel stoves) are made using a process which bonds the finish chemically to the metal.The only effective way of removing the enamel led surface is to have it sandblasted.
  • Radiator paint is specially formulated to stay white. Other types of paint may be affected by heat and turn slightly yellow. It is possible nowadays to buy heat-resistant paints in a range of colours to match or complement your interior schemes.
  • Corrosion on brass – especially on door furniture – occurs when the clear protective lacquer washes away. Corrosion can usually be removed with a patent metal polish, but heavy deposits are easier to remove with washes of a mix of 1 level teaspoon of salt and the same of vinegar mixed in 300ml (1/2pt) of hot water applied with fine wire wool.
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