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10

Substrate

Delamination / loss of adhesion

The varnish loses its bond with the substrate or the layers lose adhesion to each other - an effect visible as peeling or complete loss of the coating. It may occur immediately after painting or become visible only after months of operation.

Stratification takes three forms:

  • The entire paint system peels off from the metal substrate
  • The clear or base coat peels off as part of the system - between coats
  • The paint loses adhesion to plastic elements
Delamination / loss of adhesion

Cause

General causes - apply to all forms of delamination
  • Substrate contaminated with grease, silicone, oil, wax, sanding dust or corrosion - the most common cause of loss of adhesion
  • Inappropriate primer system for a given substrate - not every primer is suitable for every substrate
  • Insufficient thickness of the primer layer - too thin a layer does not provide adequate adhesion
  • Too smooth sanding - too little mechanical texture of the surface reduces the adhesion of subsequent layers
  • Wrong selection of hardener or thinner affects the hardness and elasticity of the coating
  • Failure to adhere to the recommended flash-off time between coats - solvent or water trapped between coats will cause adhesion loss
  • Lacquer layer too thick - ingredients not mixed in the correct proportions result in excessive thickness
  • Exceeding the maximum open time in wet-on-wet systems
Specific causes - between system layers
  • Too many layers of base applied one after the other without proper evaporation - the surface becomes rough and uneven, the colorless paint has nothing to stick to
  • Base coat applied from too far away or at too low a pressure - dry spray creates a grainy, matte surface on which the clear coat does not adhere properly
  • Failure to adhere to evaporation times between base and clear - solvent residue trapped between layers
  • Clear coat not matched to the base - chemical incompatibility between products of different systems
Specific causes - plastics
  • Incorrect or insufficient cleaning of plastic elements - some plastics require aging and heating at appropriate temperatures and the use of special products that remove adhesive agents
  • Lack of adhesion promoter or unsuitable primer for the plastic
  • The selected paint system is not suitable for a specific type of material - PP, TPO, ABS require different preparation systems

Prevention

Substrate preparation
  • Carefully inspect the substrate when degreasing - remove all traces of grease, silicone, wax and corrosion
  • Make sure the substrate is thoroughly cleaned before each subsequent step in the process
  • Use sandpaper with the appropriate gradation - do not sand too smoothly, the appropriate mechanical texture is crucial for adhesion
  • Plastic elements should be aged and heated at the appropriate temperature before cleaning and grinding
Product selection
  • Check the technical data sheet to select the correct system for your substrate
  • Use only recommended paint systems - do not mix products from different systems
  • Always apply an adhesion promoter to plastic elements before the primer
  • Select the varnishing system recommended for a specific type of material
App
  • Observe the recommended evaporation time between the application of subsequent layers
  • Once evaporated, wipe with an antistatic cloth between each coat of base coat - especially in hot climates
  • Mix the ingredients in the correct recommended proportions
  • Do not apply excessive amounts of material - observe the recommended layer thickness
  • In wet-on-wet systems, do not exceed the maximum open time
  • Use proper air pressure to avoid over-application of material

Repair

General repair rules
  • Remove all layers with poor adhesion - never cover the problem with additional layers
  • Sand the delaminating system down to a sound, firmly adherent layer
  • Sand and clean the substrate thoroughly before re-application
  • Identify and eliminate the cause before repainting - otherwise the defect will return
  • Recoat using the appropriate primer, filler and topcoat system
Repair on plastics
  • Remove the damaged paint system completely
  • Wash the element under pressure or steam
  • Wait until the element is completely dry - rest
  • Degrease and clean thoroughly
  • Rebuild the paint system based on appropriate products dedicated to a given material