Paint Layer Thickness
Paint Layer Thickness
In practice this happens a lot: after an inductive layer thickness measurement, collision repair paint jobs are rejected – on the grounds that the total paint layer is too thick. But is this actually a relevant benchmark? And if so, how much should it really be?
The German Commission for Paint and Bodywork Repair (Deutsche Kommission für Lack- und Karosserieinstandsetzung; DeKoLaKa) published a data sheet1 on this contentious issue in the spring of this year. It clearly states that increased paint layer thicknesses alone are not cause to classify vehicle refinishing as quality-deficient. The data sheet also provides guidelines for layer thicknesses for various repair methods.
Firstly, the data sheet clarifies the coating materials to be used with the corresponding substrate, and the layer structure to be used for the specific paint job – a crucial point when it comes to assessing the repair. Here, bodywork fillers and tin replacement materials form part of the substrate and are not included in the total paint thickness.
The values are not standardised even for new vehicles
In principle, the total paint thickness on a new vehicle depends largely on the production technology and the coating process. For the initial coating in industrial series production, it is usually between 80 and 130 µm – a guideline value that can vary depending on the manufacturer, location, method and workflow. However, the deviations can be even greater: in fact, increased paint layer thicknesses occur of up to twice the total paint layer thickness in ideal industrial series production.
A major German vehicle manufacturer states that the total paint layer thickness in series production can be up to 350 µm – this is due to repainting in post-processing in what are known as "Pre Delivery Inspection Centres". In practice, even higher values have been measured – this is not necessarily implausible, even for new vehicles sold as accident-free.
Different standards apply to repairs
Other application processes and coating technologies are required for manual refinishing compared to industrial series production – which naturally results in deviations in the top coat structure. There are various process sequences for collision repair paint jobs, and different paint repair systems are also used. Intact layers of paint are often not completely removed – instead they are included in the collision repair paint job and form the structural basis for the manual painting process. An increased total paint layer thickness is therefore taken into account and is entirely compliant with the standards for a professional finish.
The body repair process is a fundamental shift in the right direction. Where necessary, bodywork levelling or filling compounds are used; see above. Depending on the success of the sheet metal reshaping, the layer thickness can be several millimetres even at this stage. The problem in practice is then: when assessing the total paint layer thickness using non-destructive measuring methods (e.g. with a coating thickness gauge), it is not usually possible to measure the layer thicknesses individually. However, the measurement does include the fillers and levelling compounds which are not calculated as part of the total layer thickness. Some examples of layer structures with guideline values can be found in the information sheet.
Conclusion
The information sheet clearly states "... that no precise and conclusive statements can be made regarding the quality of the repainted repair and/or otherwise repainted vehicle body or its components on the basis of non-destructive measurement methods for determining the paint layer thickness". (Information sheet, page 13) This means that the total paint layer thickness after a repair does not count as the sole deciding factor for quality. Exception: there are actual visual or functional impairments when used as intended.
For a clear assessment, full details of the material structure must be known. However, these in-depth additional analyses carried out retrospectively are generally anything but non-destructive. In other words: they can only be used by completely sanding down the repaired area.
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1TOTAL LAYER THICKNESS
Principles for the professional assessment of paintwork on road vehicles using layer thickness measurement
Bundesverband Fahrzeuglackierer (Federal Association of Vehicle Painters)
Deutsche Kommission für Lack- und Karosserieinstandsetzung (German Commission for Paint and Bodywork Repairs)
Information sheet 010 (dated: 03/2025)