7 common industrial coatings defects and how to fix them

Note: This blogpost is relevant for manufacturers who paint on metal. If you work in another industry, read more about our other industrial coatings.

When it comes to industrial painting, even the most experienced painters can run into coating defects from time to time. In machine manufacturing, surfaces are complex. You have to consider the type of metal, the environment in your production area, leftover oils, contaminants, and salt, which can cause osmotic blistering.

“Osmotic blistering happens when water soluble salts on the surface attract water through the paint film after painting. When the surface gets wet, the salt will draw in moisture. This causes blisters that weaken the paint and will lead to corrosion of the metal underneath. That’s why proper surface preparation is important”, says Tomi Kontunen, Technical Service Specialist at Teknos.

Metal surfaces need tough, high-performance coatings that can handle tough environments, which adds more challenges.

Even with the complexity, we often see 7 very common optical coating defects. Let’s go through them one by one.

1.    Fisheyes or pinholes in paint

Have you seen these crater-like openings in the paint film? It does not look good. It can appear as the paint has poor adhesion, like the substrate is rejecting it.

Why is it happening?
Oil, grease, silicone, or other contaminants that don't mix well with the paint. Even using silicone spray at a "safe" distance can spread and cause issues with the paint.

How to fix it: Unfortunately, you have to start over. Sand off the paint, clean and redo the paint. Even then, it can be challenging. Silicone is an extremely strong contaminant and can be difficult to remove, even with solvents or other chemicals. If you experience these challenges, contact us - we're here to help.

Tip: Make sure that all equipment and the environment are completely clean and free from contaminants before you start painting. Pay extra attention to silicone. Even a tiny bit of silicone can be tricky and cause fisheyes.

2.    Curtains

Drips or runs in the paint that forms lines or curtains.

Why is it happening?
There are several reasons for causing paint curtains:

• Applying too much paint at once.
• Cold surface. When the surface is cold, the paint doesn’t level well and struggles to spread evenly. That’s when you get an uneven finish.
• Paint is too thin and runs easily.
• Holding the spray gun too close to the surface. Then the wet film becomes too thick.
• High humidity when using water-based paint.

How to fix it:

• Sand off the paint and clean the surface before repainting.
• Apply the paint with the proper wet film thickness as specified in the data sheet.
• Adjust the spray gun settings for better control and allow proper drying time between coats. Check the technical data sheets for more help.
• Use a brush to smooth out drips if possible.
• Keep moving the spray gun to spread the paint evenly.
• Increase the distance between the spray gun and the surface.

Did you know?
When you apply a really thick layer of paint, like several millimeters, it’s going to wrinkle first. As it keeps drying, you’ll see those alligator cracks start to form. Too much paint also means it can run – especially if the wet film thickness is more than double the recommended amount.

To avoid this, think about your painting order. Start with the more difficult parts, and save the easier areas for last.

Why – you might wonder? If you start with the easy areas first, you'll have a layer of paint there. Then, when you go back to spray the difficult parts, you’ll end up adding more and more paint to those easy areas. Before you know it, there's too much paint, and it starts to run. That's why I recommend starting with the difficult parts. Getting the right amount of paint in the right order is important.

3.    Orange peel paint

A textured finish that looks like the skin of an orange.

Why is it happening?

• Low paint and surface temperatures: Using paint that's too thick or painting in cold conditions can prevent the paint from leveling as well as it would at room temperature. When you spray on a cold surface, the paint immediately cools down to match the steel’s temperature. This can cause uneven coverage and a bad overall result.
• Poor atomization of the paint, spray settings, nozzles, colour viscosity: The paint isn’t breaking down/atomizing properly as it's sprayed. It could be due to incorrect spray gun settings, using the wrong type or size of nozzle, or the paint being too thick or too thin. In other words, there is not enough pressure and it’s leading to poor atomization of the paint.
• The gun too close to the object: Holding the spray gun too close to the surface can cause the paint to build up unevenly and create a bumpy texture.
• Fast evaporating solvents in paint: If the solvents evaporate too quickly, it can cause the paint to cure unevenly and create a rough surface.
• Low humidity when painting with waterborne paint: Low humidity can cause water-based paint to dry too quickly, leading to a textured, uneven finish.

How to fix it:

• Sanding down and repainting: If the surface is already bumpy, sand it down until it's smooth. Then repaint, making sure to follow the right settings and conditions to avoid the same problems.
• Adjust spray pressure: Make sure the spray gun is set to the right pressure for a smooth finish, and use the correct nozzle size to ensure better atomization of the paint. Check the technical data sheets for the right settings.
• Ensure proper thinning of paint: Make sure the paint is in right viscosity. If it's too thick, thin it out according to the manufacturer’s instructions.
• Maintain optimal temperature and humidity levels during application: Paint in an environment with the right temperature and humidity to prevent uneven drying. Look at the product guidelines for the best temperature and humidity.

4.    Alligatoring

Small cracks show up in the topcoat. The coating looks like the skin of an alligator. That's why we call it alligatoring.

Why it happens:

• Painting or drying the paint in too high temperatures. The underlying surface shrinks or moves at a different rate than the topcoat.
• Painting over a layer that hasn’t fully dried, trapping solvents inside. This can also happen if you paint in windy conditions and the surface dries too quickly.
• Using too much paint can create an excessively thick film, especially with drops forming on horizontal surfaces.

How to fix it:
Sand down the cracked area and repaint it. Remember to check technical data sheets and instructions for drying temperatures.

5.    Wrinkled paint

Wrinkled paint, also called lifting, is when the surface looks frosted and has small creases or wrinkles that can go through the entire paint layer.

Why it happens:

• The paint surface dries faster than the rest of the paint film. This can happen in windy conditions or hot sunshine. It forms a leather-like texture.
• Applying the paint too thickly or drying it at too high a temperature.
• Using paint with strong solvents or applying it over layers with strong solvents.

“A good example is when a xylene-based topcoat is applied over a white spirit-based primer. Xylene is a stronger solvent than white spirit, which can cause issues like softening or dissolving the primer. This can lead to poor adhesion, cracking, or curing unevenly. In short, using different solvents can cause problems between the layers”, says Tomi Kontunen, Technical Service Specialist at Teknos.

How to fix it:

• Sand off the paint and clean the surface before repainting.
• Adjust the drying temperature to be more moderate.
• Sand down the wrinkled area and repaint it.

6.    Peeling paint

The paint peels off, either from the surface it’s applied to or between different paint layers.

Why it happens:

• Poor surface preparation or painting conditions.
• Inadequate cleaning of the surface or between paint layers.
• Using materials that don’t work well together, either between the primer and the surface or between paint layers.
• Waiting too long between applying coats of paint.

How to fix it:

• Remove the peeling paint down to a stable layer or the bare surface.
• Make sure to properly prepare and clean the surface before repainting.

Did you know?

If there is moisture or dust on the surface, the paint can start peeling. This often happens in winter when cold metal parts are moved from outside to inside. This causes condensation to form on the surface. To remove the moisture, you need to wait until the metal warms up and the moisture disappears. That’s where the dew point comes in - it’s the lowest temperature where water can condense on a surface. The surface temperature should always be at least 3 degrees higher than the dew point.

To get rid of dust, use compressed air or a vacuum cleaner.

7.    Bubbles in paint

The paint can develop bubbles both on the surface and inside the layers. In most cases, it's visible on the top of the paint, but there can also be hidden bubbles in paint within the layers that are only noticeable if the paint film is cut and closely inspected.

Why it happens:

• Rust, contamination, or moisture on the painting surface.
• Trapped solvents within the paint.
• Air bubbles trapped during spraying, which remain in the paint film.

How to fix it:

• Sand down the affected area and repaint.
• Thoroughly clean the surface before painting.
• Ensure the painting surface is dry, and always paint when the object's temperature is well above the dew point.

Key takeaway on coating defects

Now that you've read about common coating defects and how to fix them, remember this: always make sure to prepare your surfaces properly and check the technical data sheets for painting instructions.

It's often difficult to pinpoint just one reason for surface defects, as they can result from a combination of several issues. On the same surface, you might find bubbles, pinholes, and craters. For example, a crater might be a bubble that has burst after the paint has dried and the surface hasn’t had time to level out. It’s the same phenomenon, just at different stages.

If things don't go as planned, you can always come back to this guide or reach out to us for help. We’re here to assist you in getting the best results.