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.