SHRINKAGE / EDGE MAPPING

Description of problem:  26-_shrinkage-_edge_mapping.jpg
    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.