How to recognise powder coating? Key differences

What is powder coating?

Powder coating is a method of applying paint in the form of a dry powder to a metal surface. Steel and aluminium are the materials most often coated this way, although the technology is also used on other materials that can withstand high temperatures. The powder itself is applied electrostatically, so it clings evenly to the part, and the whole part then goes into an oven, where the powder melts and cures.

That is a big difference from conventional wet painting. There are no solvents and no evaporation stage. After baking you get a dense, hard film with high mechanical and chemical resistance.

In reality it's not just the powder that matters, but the whole process. A badly prepared part or the wrong cure temperature can ruin even a good material. That is why professional coating shops control every stage - from surface preparation right through to measuring the thickness of the finished coating.

Each of them behaves a little differently - polyester copes well outdoors and is UV-resistant, which is why it often ends up on fencing, structural steelwork and architectural elements. Epoxy powders stand up better to chemicals but chalk badly under prolonged sunlight, so they are mainly specified for interior use.

Read also: Types of powder coating - differences and uses

How to recognise powder coating by the look of the surface?

Most of it shows the moment you pick the part up. A powder-coated finish usually looks even and gives the impression of being "fuller" than conventional wet paint. There are no streaks, runs or brush marks. Even over large panels the gloss level stays consistent.

It shows up best when you catch the surface in the light. With poor-quality coating, differences in texture or film thickness quickly start to stand out. With well-executed powder coating the surface stays uniform. The finish is described by 2 independent characteristics: gloss level and surface texture. Gloss is measured with a glossmeter and quoted as a percentage, and there are 5 levels - from matt (up to 20%), through semi-matt, semi-gloss and gloss, up to high gloss (above 85%). Regardless of the gloss, the surface can be smooth or deliberately textured, for example a fine texture or a heavier textured finish.

Texture is not a defect - in many cases it is used deliberately, especially on parts that see daily use, where it helps to hide minor imperfections and disguise the marks of everyday handling. That is why pallet racking, metal cabinets and machine components often have a slightly rough surface.

The feel of the surface soon gives the quality away

A powder-coated surface is noticeably harder than most conventional wet paints. It's not a "glass" effect, though. A good coating has a slight drag under the finger and feels dense. On fine textures or semi-matt surfaces you can easily feel a delicate texture. The coating should not be tacky and should not give under a fingernail.

If after a few months of use the surface is still smooth and there is no wear-through from normal contact with hands or tools, that usually means the process was done correctly. Touch also helps to detect process problems. The warning signs are:

Defects like these are often the result of poor surface preparation or contamination present during coating.

Read also: The most common problems in powder coating and how to solve them

Durability says more than looks alone

A freshly coated part almost always looks good. The real test only starts in use. That is when the difference between a plain decorative layer and a properly applied protective coating comes out. One of the reasons powder coating is used is that the film copes well with:

• impacts,
• abrasion,
• contact with detergents,
• moisture,
• changing temperatures.

Of course, that doesn't mean it is resistant to everything. If you hit the edge of a part hard with a metal tool, damage can occur. It's more about everyday use, where the coating has to put up with being knocked about, cleaned and exposed to its surroundings without flaking early.

What are the main differences between powder coating and conventional painting?

The biggest difference is in the application technology itself. Powder coating uses no liquid solvents. The material goes onto the part as a dry powder and only flows out into a continuous film during the bake.

The end result is usually more mechanically resistant than with conventional wet paints. The film is thicker and tougher, and chips less often in everyday use. But conventional painting still has its place - it works well on very large structures or on parts that cannot be baked in an oven. The problem comes when high repeatability and surface resistance are what count.

That is why powder coating has dominated volume production for years. On metal furniture, white goods or industrial housings every part should look almost identical. Powder technology handles that well. Then there is the economics of production - some of the unused powder can be reclaimed and reused, which limits material losses.

Why does surface preparation matter so much?

This is the stage the customer usually never sees, yet it is the one that most often decides how long the whole coating lasts. Even the best powder won't last on badly prepared metal. Before coating, the part goes through several process steps:

Only then does the part go into the spray booth. If grease, dust or moisture is left on the surface, the powder may not bond properly to the substrate.

Read also: Surface preparation for powder coating - stages, mistakes and best practice

Where is powder coating most commonly used?

This technology moved beyond fencing and railings a long time ago. Today powder coatings go into practically every industry that works with metal. The most commonly coated items are:

• metal furniture,
• structural steelwork,
• equipment housings,
• white goods,
• machine parts,
• pallet racking,
• medical equipment,
• alloy wheels,
• barbecues and stoves,
• road signs.

In many cases the coating is not meant to be purely decorative. It protects the metal against moisture, detergents, mechanical damage and corrosion. Industrial housings and control cabinets are a good example. Parts like these often work in harsh conditions - high humidity, changing temperatures or regular contact with industrial chemicals - and the coating has to withstand that for years.

Read also: What items can be powder coated?

How to assess the quality of powder coating?

A good coating is even, hard-wearing and colour-stable. You can see that on inspection. If the surface has discolouration, varying gloss levels or small blisters, the process was most likely done incorrectly. Problems also arise when the part was baked for too short a time or at the wrong temperature.

In professional coating shops, quality control typically covers:

For the end user, though, what matters most are the symptoms visible in normal use. A good powder coating should not lose its gloss quickly, chip at a light knock or start corroding at the edges. Colour consistency also matters a great deal. In volume production every part has to look the same, regardless of batch size.

Read also: How to choose the right powder coating - practical tips

Why does industry favour powder coating?

The reason is simple - durability, repeatability and control over the process are what count. The manufacturer doesn't want warranty claims coming back a few months down the line. The coating shop needs stable process parameters. The end customer expects the coating to still be there after the first winter, and after a wipe-down with detergent.

Powder coating meets those demands, which is why you find it both in large production plants and in small coating shops running short batches. Today's powder coatings also do far more than they did 15 years ago. Better UV resistance, lower cure temperatures and greater control over surface texture mean the technology keeps finding new applications.