Orange peel refers to texture in the finished painted surface similar to that of an orange skin. Excessive orange peel is commonly caused by a paint process in which the paint does not sufficiently ‘flow out’ on the part in either the application, flash, or curing phases.
This is a easy term to remember, because it is actually referring to the peel of an orange. The peel of an orange has a bumpy texture. Now if you look close at all paint jobs, even new from the factory, there is orange peel present. The only time there is not, is if the surface has been cut and polished (buffed) like a show car. However, it is the excessive orange peel that become the problem and becomes an undesirable finish to the customer.
When we were discussing spraying techniques and how the spray gun atomizes paint, we said the paint is broken into tiny drops so that it could be transferred from the cup to the car. When the drops are too big or too dry when they hit the panel being finished, the drop will not flow together and level out as they should. In order to reduce the orange peel to an acceptable amount is to find a way to make the paint drops smaller or a way to spray the paint wetter.
Orange peel is often caused because of poor gun adjustment as the paint is being applied, although it also can be caused by incorrectly reducing the coating before application. Gun setup and adjustment are critical to a smooth and flat appearance of a coating. If the needle/nozzle combination is not specifically matched to the coating being applied, the air pressure – especially when using an HVLP (high volume low pressure) gun – is not sufficient to atomize the paint properly. –
- Improper gun adjustment and techniques. Too little air pressure, wide fan patterns or spraying at excessive gun distances causes droplets to become too dry during their travel time to the work surface and they remain as formed by gun nozzle.
- Extreme shop temperature. When air temperature is too high, droplets lose more solvent and dry out before they can flow and level properly.
- Improper dry. Gun fanning before paint droplets have a chance to flow together will cause orange peel.
- Improper flash or recoat time between coats. If first coats of enamel are allowed to become too dry, solvent in the paint droplets of following coats will be absorbed into the first coat before proper flow is achieved.
- Wrong thinner or reducer. Under-diluted paint or paint thinned with fast evaporating thinners or reducers causes the atomized droplets to become too dry before reaching the surface.
- Viscosity is too high.
- Low shop temperature.
- Too little thinner or reducer.
- Materials not uniformly mixed. Many finishes are formulated with components that aid coalescence. If these are not properly mixed, orange peel will result.
- Substrate not sanded thoroughly.
- Unsuitable combination of solvents or low quality solvents.
- Application thickness is either too little or too much.
- Use proper gun adjustments, techniques, and air pressure.
- Schedule painting to avoid temperature and humidity extremes.
- Select the thinner or reducer that is suitable for existing conditions. The use of a slower evaporating thinner or reducer will overcome this.
- Allow sufficient flash and dry time. Do not dry by fanning.
- Allow proper drying time for undercoats and topcoats. Not too long or not too short.
- Reduce to recommended viscosity with proper thinner/reducer.
- Stir all pigmented undercoats and topcoats thoroughly.
- Prepare and sand substrate correctly.
- Follow recommendations on technical data sheets.
- See tech data for correct choice of spray nozzle.
- In minor cases, wait until the paint is fully dry and polish with a coarse compound and then a fine compound.
- For mild cases, sand and polish using recommended materials and techniques.
- In extreme cases, sand down to smooth surface and refinish, using a slower evaporating thinner or reducer at the correct air pressure.
- DIY Auto Body and Paint, Paint Defects, data of access: 21 July 2016, http://www.collisionblast.com/paint-defects/
- Axalta Coating Systems, Paint Defects Manuel, data of access: 21 July 2016, http://www.axaltacs.com/content/dam/NA/HQ/Public/Axalta/Documents/Brochures/Axalta-Paint-Defects-Manual.pdf
- Lusid Technologies, Painting Defects, data of access: 21 July 2016, http://www.lusidtechnologies.com/index.php/paint-defects