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Blistering

Definition

In wet weather, a small quantity of water vapour is absorbed into the paint system and will evaporate again in dry weather (osmosis). This process is normal and does not harm a perfectly matched paint system. However, poor processing of the undercoat materials will leave hygroscopic/water-soluble substances (salts) behind as contaminants, which cause a local concentration of humidity, lifting the paint film into blisters. Blisters can occur in many sizes and patterns with varying frequency and can form between individual layers or beneath the entire paint system. In dry weather, most blisters will recede.

Blasenbildung

Causes

  1. The surface to be painted (filler, bare metal, etc.) was not cleaned thoroughly. Contamination from salt residue, for example, dirty sanding water or hand sweat, was left on the surface before painting. The blister pattern may indicate the cause (beading = wipe marks, prints = finger or hand prints)
  2. Wet sanding of polyester products without sufficient time to allow water to evaporate before application of undercoats and topcoats.
Blasenbildung
10x magnification
Blasenbildung
Scanning electron microscope image: Salt crystals in an open blister. 100x magnification.

HOW TO AVOID

  1. Thoroughly clean the areas to be painted with clean tap water. Change sanding and cleaning water regularly, especially in winter, when vehicle paintwork is covered in salt. Finally (depending on the substrate), clean the area with Glasurit 700-1 Cleaner, Glasurit 541-5 Wax and Silicone Remover or Glasurit 360-4 Metal Cleaner.
  2. Do not wet sand polyester products, use dry sanding only.

REPAIR

Sand down the paint system to a sound surface. Refinish using the recommended undercoats and topcoats.