Why Is the Clear Coat Rough or Matte After Spraying?

Short answer

Clear coat is usually rough, dry, grainy or matte after spraying because partially dried material has reached the surface. This is called dry spray. The clear coat did not have enough time or material to flow out and level properly, so it did not create a smooth glossy surface.

Dry spray is mainly caused by spraying from too far away, moving too fast, high temperature, draughts or applying the layer too thinly. Clear coat must be applied so that it reaches the surface still wet enough and can then flow out into a smooth layer.

What does dry spray mean?

Dry spray is a condition where droplets of clear coat start drying before they reach the painted surface, or they land on the surface in a layer that is too thin. The clear coat then does not join into a smooth continuous layer, but creates a rough, dry, matte or grainy surface.

At first glance, the surface may look like fine orange peel, dust, small grains or a dry matte film. Instead of flowing out and creating gloss, the structure of individual partially dried droplets remains visible on the surface.

Why is the clear coat rough after spraying?

A rough surface usually means that the clear coat was too dry when it reached the surface. The most common cause is holding the spray can or spray gun too far from the surface. The longer the clear coat travels through the air, the more time it has to partially dry before landing.

A similar problem occurs when the hand movement is too fast. Too little material reaches the surface, the layer is too weak and the clear coat does not have enough material to flow out properly.

Why can clear coat look matte?

Clear coat can look matte when it has not flowed out and levelled correctly. Gloss appears only when the clear coat layer joins into a smooth surface. If the clear coat reaches the surface too dry or in a layer that is too thin, the surface remains matte, drier and less transparent.

A matte appearance does not always mean that the clear coat itself is bad. Very often, it is an application problem where the clear coat was not applied under the right conditions or was not applied wet enough.

Most common causes of rough or matte clear coat

• spraying from too far away,
• moving the spray can or spray gun too fast,
• clear coat layer applied too thinly,
• high temperature during application,
• direct sunlight or a hot painted part,
• draughts or strong air movement,
• waiting too long between spray passes on the same area,
• insufficient overlap of spray passes,
• unsuitable thinning or incorrect spray gun settings,
• too little material applied.

What role does temperature play?

High temperature speeds up solvent evaporation. The clear coat then dries faster and may become dry before it has enough time to flow out correctly on the surface. This applies especially when spraying in the sun, in a hot garage or on a part heated by sunlight.

The ideal application temperature is stable and approximately 20–25 °C. It is important that not only the air, but also the painted part and the material have a similar temperature. A surface that is too hot can cause the clear coat to flash too quickly, resulting in a rough or matte finish.

Why is spraying from too far away a problem?

If the spray can or spray gun is too far from the surface, the clear coat travels through the air for longer. During this time, solvents evaporate and droplets partially dry. Instead of wet clear coat, drier material reaches the surface and does not join into a smooth layer as easily.

The result can be a rough, dry or matte surface. With a spray can, it is therefore important to keep the correct distance from the surface and work smoothly. With a spray gun, correct pressure, material flow and spray pattern are also important.

Why is a layer that is too thin a problem?

Clear coat needs a certain amount of material so it can flow out across the surface. If the layer is too thin, the clear coat does not join into a smooth continuous layer and remains dry or matte.

This does not mean that the clear coat should be applied in one extremely heavy coat. A layer that is too heavy can run, become milky, flash off poorly or create other defects. Correct technique and a balanced amount of material are essential.

How should clear coat flow out and level?

After application, clear coat does not instantly behave like a finished surface. During the first minutes after spraying, the layer gradually flows out, joins together and levels. This is the process that creates a smooth and glossy appearance.

This process can take place during approximately the first 30–60 minutes, depending on the type of clear coat, temperature, layer thickness and application conditions. If the clear coat is applied too dry, too thinly or under unsuitable conditions, it does not have enough material or time to level properly.

Can rough or matte clear coat be repaired with another layer?

Sometimes another correctly applied layer can partly improve the appearance, but it is not guaranteed. If the previous layer is very dry, rough or contaminated, the next layer may not fully level the surface and the defect can remain visible.

If the surface is already very rough, it is often better to let the clear coat cure sufficiently, lightly sand the surface if needed and then continue with the correct process. Fresh soft clear coat should not be sanded too early.

What not to do when the clear coat is rough or matte

• do not try to immediately flood the problem with an extremely heavy coat,
• do not add another layer without checking whether the previous layer has flashed off correctly,
• do not sand fresh soft clear coat too early,
• do not continue spraying under the same conditions that caused the problem,
• do not keep spraying in direct sunlight, draughts or on a hot part.

How to prevent the problem

• spray at a suitable temperature, ideally around 20–25 °C,
• do not spray in direct sunlight or on a hot surface,
• avoid draughts and strong air movement,
• keep the correct distance between the spray can or gun and the surface,
• move smoothly, but not too fast,
• keep an even overlap of each spray pass,
• apply a wet enough layer so the clear coat can flow out,
• avoid both extremely thin and extremely heavy layers,
• with a spray gun, set the correct pressure, material flow and spray pattern,
• test the technique on a test part before spraying a larger surface.

Does this also apply to effect paints?

This article mainly applies to clear coat. Effect paints such as Candy, Chameleon, Pearl or Ghost Pearl are not applied in the same way as final clear coat. With effect paints, it is usually important to apply thin, controlled and even coats.

Clear coat is the final protective layer that should create gloss, depth and a smooth surface. That is why correct flow and levelling are important. Effect paint should not be “flooded” in the same way as clear coat.

When does the surface need to be sanded and recoated?

If the clear coat is only slightly dry or less glossy, it can sometimes be improved after curing by fine sanding and polishing. However, if the surface is very rough, grainy, uneven or matte, it may be necessary to let it cure, sand it and apply clear coat again correctly.

It is always important to let the clear coat cure sufficiently first. Sanding or polishing fresh clear coat too early can cause additional defects, marks, smearing or damage to the layer.

Summary

• Rough, dry, grainy or matte clear coat is often caused by dry spray.
• Dry spray happens when clear coat reaches the surface already partially dry or in a layer that is too thin.
• The most common causes are high temperature, spraying from too far away, moving too fast, draughts or applying the layer too thinly.
• Clear coat must reach the surface wet enough so it can flow out and level.
• Correct levelling of clear coat happens during the first minutes to tens of minutes after application.
• Effect paints are not applied in the same way as clear coat and should not be flooded in a heavy layer.
• If the surface is very rough or matte, it is often necessary to let the clear coat cure, sand it and recoat it correctly.