Scarring and/or incidence in the marginal area
Scarring or grinding marks in the edge zone area can have many causes. Here you will find the most common ones.
- Sources of error:
- The grit of the sandpaper for the final sanding was too coarse (P180 instead of P240). Run-out zones are disturbed by deep and sharp sanding grooves and mark each other.
- The filler layer thickness is too high and the material was not dried long enough.
- Material viscosity is too high (material is thick).
- Flash-off time not observed.
- Substrates not sanded cleanly. Lax matting of the substrates does not produce an excellent surface and may result in markings on the material in the unsanded zones.
- Substrates react to solvents.
- Poor or no isolation of filler areas.
- Fault prevention:
- Finer sanding prior to filler application. P240 eccentric sanding is suitable for the filler end sanding. Use P400 for the outer edge zone.
- Do not just „fondle“ run-out zones with fleece. These should also be ground even so that they can „cleanly“ adapt to the surface after final sanding.
- Observe the flash-off times specified by the manufacturer.
- Seal substrates with suitable material.
- Thin down filler materials with a high solids content slightly to allow the material to run. Spray filler can also produce hard edges or sink marks!
- Repair method:
- For 2-K Uni 1-coat or 2-coat Uni surfaces, level and finish with a block.
- Markings that are visibly visible in the metallic basecoat structure after clearcoat application must be repainted. Due to the metallic particles in the base material, it is not possible to „conceal“ the substrate defects with a surface finish alone. In this case, the surface must be ground flat and coated again with basecoat and clearcoat. The metallic particles literally lean into the „incorrectly“ applied substrate and make it „shine“ by reflecting light.
- What happens in this process?
- Substrates that have been „patted, fumbled, or stroked“ have a certain amount of graininess. If this has not been thoroughly removed prior to material application, it will be visible in subsequent coatings.
- Freshly painted surfaces still look very smooth when wet. After a certain drying time, solvents escape and, depending on the solids content of the material, the material „sinks“ into the scars. In the case of subsequent sanding, this can lead to additional cracks at the material edge.
Solvents migrate into the substrate and attack edge zones if the substrate is not ground flat. This can lead to a lifting of the edges. This is how well-known edge zone markings are created
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