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Coating defects

APPLICATION DEFECTS, CAUSES AND SOLUTIONS

There are a lot of different factors which can affect the outcome when trying to get a good surface finish. We would like to help you, so we prepared this special section on “APPLICATION DEFECTS, CAUSES AND SOLUTIONS”. We will identify the various defects on painted surfaces, look at the factors which cause them and give you a solution for their correction. A combination of that ensures you a quality result and a long lasting finish.
We wish you good work and a lot of success!

Blisters

Causes:

  • Too short flash off times between the coats
  • Too thick primer coat
  • Water polluted compressed air
  • Too high air humidity (over 80 % at 2K materials)
  • Condensed water due to temperature fluctuations in the compressed air installation 

Prevention:

  • Flash off between coats min. 5 -10 min/20°C, or until surface is mark free
  • Compressed air should be dry and clean
  • Avoid the formation of condensed water in the air installation. Keep a stable temperature and humidity

Traces of sanding in a top coat

Causes:  

  • Sanding of the primer with unsuitable (too rough) abrasive paper
  • Sanding of the substrate with unsuitable (too rough) abrasive paper 
  • Insufficient putty isolation prior to application of the top coat
  • Too low viscosity of top coat

Prevention:

  • Use abrasive paper of prescribed grit
  • Sanding marks with a fine abrasive paper
  • Isolate thoroughly puttied repairs with filler
  • Follow the prescribed viscosities of top coats
  • Follow the prescribed drying times
  • Follow the prescribed coating thickness

Bad adhesion to the surface

Causes:

  • Poorly prepared, contaminated surface (grease traces, finger prints, dust etc.)
  • Use of the materials, which are not suitable for certain types of substrates
  • Thinning of material with unsuitable (not original) thinner

Prevention:

  • Clean surface thoroughly before painting
  • Always check which material is suitable to a certain type of substrate
  • Use of recommended thinners

Surface soaking

Causes:

  • Not dried through, not cured old coat
  • Too thick thickness of old coating

Prevention:

  • Follow the prescribed drying times
  • Follow drying through times with synthetic (KH) coats
  • Isolation of problematic surfaces
  • Follow the prescribed thickness for coats

Sagging

Causes:

  • Incorrect material viscosity 
  • Too thick film thickness 
  • Unsuitable spray gun (nozzle), pressure
  • Too cold material or substrate or too low room temperature
  • Use of unsuitable thinner

Prevention:

  • Follow technical instructions for use
  • Use a suitable spray gun
  • Warm the object and material to room temperature +20°C
  • Use of a recommended thinner

Craters

Causes:

  • Wax, grease, silicone contaminated surface
  • Compressed air contaminated through condensed water or oil residue
  • Use of silicone, polishing agents or sprays in the vicinity of painting area
  • Insufficiently cleaned surface before coating

Prevention:

  • Before coating clean the surface thoroughly with Anti silicone cleaner 
  • Regular maintenance of oil and water separators (filters)

Matt effect (gloss decrease)

Causes:

  • Too high air humidity
  • Surface soaking
  • Hardener defects – hardener reacted with air humidity
  • Humidity in compressed air supply

Prevention:

  • Follow technical instructions for the application of material
  • Keep hardener cans sealed properly
  • Enable sufficient air flow (during drying)
  • Follow drying times
  • Use the recommended hardener

Bad leveling

Reasons:

  • Unsuitable (too high) viscosity
  • Unsuitable application technique
  • Unsuitable working temperature
  • Use of unsuitable thinner
  • Unsuitable spray gun (nozzle), pressure

Prevention:

  • Follow technical instructions for use – viscosity and temperature
  • Use of prescribed spray gun (nozzle)
  • Use of prescribed thinner

Repair of incurred damage:

  • Sand to filler and repeat painting of top coat as prescribed

Popping

Reasons:

  • Incorrectly dried-through filler
  • Trapping of solvents and air because of too high film thickness
  • No flash off between coats
  • Wrong hardener and thinner
  • Interrupted drying (not following drying time)

Prevention:

  • Apply the prescribed coat thickness
  • Wait between the first and the second coat 10 – 15 min/20 °C or until mark-free surface
  • Regular check of activation and temperature of a drier
  • Follow prescribed flash off times between coats and final flash off
  • Use the prescribed hardener and thinner

Repair of incurred damage:

  • Sand to sheet metal and repeat painting of top coat

Sandy surface

Reasons:

  • Isocyanate hardener for 2K materials reacted with air humidity

Prevention:

  • After opening the packaging with isocyanate hardener, use it up as soon as possible or
  • Close well
  • Before repeated use of hardener from the already opened packaging: check hardener, which should be clear, colourless and without any floating particles

Repair of incurred damage:

  • Sand to filler and repeat painting of top coat

Incompatibility of the materials

Reasons:

  • Mixing of enamels produced with different binders (resins), which are incompatible or only partially compatible. Example: MOBIHEL Enamel and MOBIHEL 2K acrylic enamel (defect size depends on ratio of different materials)

Prevention:

  • Follow instructions for product use
  • Mix only mixing enamels from the same quality series of MIX-es

Repair of incurred damage:

  • Sand to filler and repeat painting of top coat

Extended drying time

Reasons:

  • Too heavy coats
  • Low ambient temperature 
  • High relative humidity

Prevention:

  • Follow instructions for product use

Poor hiding power

Reasons:

  • Insufficient colour coat thickness or number of colour coats applied
  • Too much thinner added to colour

Prevention:

  • Apply the prescribed coat thickness 
  • For pigments with poor hiding power use coloured filler
  • Follow instructions for product use