Description of problem:
Shrinkage/edge mapping occurs when 2 adjacent substrates react differently to the solvents present in the topcoat or when the roughness between the 2 adjacent substrates is different.
Causes:
- Area is not isolated or isolated with an unsuitable filler.
- Filler is incorrectly applied.
- Wrong mixing ratio, too thin, or sanded too much to where substrate is showing.
- Insufficient drying or curing of substrate.
- Excessive film thickness.
- Sanding paper too coarse.
Preventive measures:
- Apply solvent test to identify soft substrates.
- Avoid applying thick coats of filler with little flash off time so that solvent is not trapped within the film.
- Avoid sanding though to substrate and sanding too coarsely.
- Apply putty only to bare metal.
- Apply proper isolating primer and follow recommendations.
- Ensure preparatory materials dry properly.
Remedy:
- Dry topcoat thoroughly.
- Sand damaged area, isolate and repaint.
- When in doubt, remove all the way to the bare metal. Apply wash primer and respray.
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