Advice on paint defects

Loss of Adhesion

Definition

Loss of adhesion can manifest itself in 2 different ways. First – where a total lack of adhesion occurs below the entire paint film. Second – where a lack of adhesion occurs between coats.

10 x magnification Reverse side of a flake of paint removed from a fine sanded Aluminium substrate (with oxide residue adhering). 50 x magnification Reverse side of a flake of paint removed from a coarse sanded bodywork surface (with metal and rust residue adhering). 50 x magnification

Causes

Loss of adhesion can occur when:

  1. Substances which can cause adhesion failure are left on the substrate (e.g. silicon, oil, grease, wax, rust, sanding residue, etc.) 
  2. An unsuitable primer or surfacer was applied to the substrate.  
  3. Insufficient sanding was carried out to the substrate. 
  4. Primer or base coats were applied too dry or too thin. 
  5. Poor drying conditions.

How to avoid

To avoid the result of loss of adhesion to the substrate, always use the correct type of primer and/or surfacer for the substrate (e.g. for aluminium, steel or plastic etc.). Only apply primers as per specification (see Technical Data Sheets or Tech Data on the cans.) Do not apply coats too thick. Thoroughly clean the substrate before application of paint materials.

Repair

Remove all coats with poor adhesion. Thoroughly sand and clean the substrate. Repaint using the correct choice of primer and/or surfacer and/or top-coats.