Painting defects

Below we have provided you with a list of the most common defects in painting and coating. For the errors you will find the possible causes and tips on how to avoid them.

Assistance

Flaking, peeling

Cause
  • Unsuitable coating system (lean on fat)
  • Change of the substrate
Cause
  • Substrate reversible or not cured
  • Pre-materials revised too early
  • Layer thicknesses that are too high
  • Drying times too short
  • Sandpaper too coarse
Avoidance
  • Solvent test
  • Filler only on bare sheet metal
  • Insulate with a 2Pack-filler; spray the filler in several thin coats and observe flash-off times.
  • Ensure proper drying of the starting materials
  • Do not grind too roughly
  • Observe processing instructions
Cause
  • Silicone contamination (e.g. hand cream, welding spray, neon tubes, sealants containing silicone, etc.)
  • Residues containing oil, wax, grease
  • Spray air contaminated by condensation or oil residues
  • Dust incidence
  • Dew fall and moisture exposure during drying and curing
  • Exhaust air time too short during heat curing
Avoidance
  • Silicone-free hand creams (Stokolan)
  • Extreme cleanliness (when processing hammertype coatings complete separation incl. wash thinner!)
  • Careful cleaning of the substrate before starting the painting process
  • Regular maintenance of the spraying equipment
Cause
  • Residues of chemical pretreatment of sheet metal
  • Substrate not sufficiently dried out and cleaned
  • Pores/voids not ground out
  • Polyester materials not insulated
  • Spray air contaminated
  • Condensation due to temperature fluctuations
  • Hand sweat
  • Salts and minerals in grinding water
  • Influence of humidity during filming
  • Inclusions from porous substrate
  • Too short flash-off time for baking enamels
  • Lack of primer
Avoidance
  • Allow pre-materials to dry out well, careful cleaning of the substrate
  • Polyester products insulate
  • Carefully grind out or fill in shrinkage marks
  • Avoid condensation
  • Ensure clean spray air, regularly check oil and water separators
  • Use demineralised water for cleaning
Cause
  • Influence by interfering substances from the subsurface
  • Excessive humidity during drying/curing
  • Insufficient ventilation during drying/ curing
  • Condensate precipitation
Cause
  • Exceeding the storage time
  • Not stirred or not stirred sufficiently
Cause
  • No correct, uniform base
  • Not sufficiently stirred
  • Layer thickness too low
  • Viscosity too low
Avoidance
  • Also stir vertically
  • Process viscosity and film thickness according to specifications
  • Use light background/ primer
  • Spray neutral substrate
Cause
  • Paint contamination
  • Incompatible addition of paint or thinner
Avoidance
  • Work cleanly. Sieve material if necessary
  • Mix only compatible coatings and thinners
Cause
  • Exceeding the pot life
Cause
  • Sprayed too wet, too dry, too thin, too opaque
  • Spray gun (nozzle), spray pressure not according to regulations
  • Surface weathered by environmental influences
  • Deviation in the series painting (multiple shades)
  • Substrate is too dark, e.g. with lead-free top coats (red, yellow, orange)
  • Not sufficiently stirred
Avoidance
  • Use recommended primer
  • Colour comparison (sample sheet)
  • Coating “droplet method
  • Stir not only horizontally, but also vertically (if necessary, mechanically with compressed air stirrer).
Cause
  • Peroxide residues in the wood (from bleaching)
Avoidance
  • Allow peroxide to decompose completely by heat or ammonia before painting
  • Use suitable hardener
Cause
  • Absorbent substrate
  • Layer thickness too low
Cause
  • Absorbent substrate
  • Exposure of fresh coating to moisture (white tint at higher temperature and humidity)
  • Too high pigment content due to inadequate agitation
  • Disturbances during drying and curing of the coating
Cause
  • Substrate not sufficiently pre-treated
  • Condensation due to temperature fluctuations / dew point undershoot
  • Wrong paint system
  • Drying times / flash-off times too short
  • Insufficient dissolving of the substrate due to exceeding the recoat time (especially with 2Pack-EP and PU systems)
Avoidance
  • Observe manufacturer information
Cause
  • Too high film thickness of the base coat
  • Too short intermediate and final flash-off times of the base coat
  • Incorrect mixing ratio of clear coat/hardener
  • Poor intermediate adhesion
Avoidance
  • Adhere to the layer thicknesses of the basecoat according to the product information.
  • Observe the intermediate and final flash-off times specified in the product information.
  • Observe mixing ratio of clearcoat to hardener according to product information.
Cause
  • Insufficient cleaning, drying (annealing)
  • Unsuitable adhesion promoter
Avoidance
  • Anneal before cleaning
  • Thorough cleaning
  • Evaporation of the cleaning agent
Cause
  • Improper storage
Cause
  • Grinding through to the substrate
  • Not isolated
  • Insulated with unsuitable filler
  • Filler not processed according to instructions
  • Substrate not thoroughly dried
Avoidance
  • Solvent test
  • Insulate with a 2-component filler; spray the filler in several thin coats and observe flash-off times.
  • Avoid cut-throughs
Cause
  • Incorrect hardener
Avoidance
  • Close hardener container after use
  • Mixing ratio clearcoat / hardener according to product information
Cause
  • Not fully cured undercoat, e.g. fresh synthetic resin paints
  • Unsuitable substrate, e.g. non-solvent-resistant plastics
  • Too thick layers
Avoidance
  • Observe prescribed drying times
  • Remove or isolate solvent-sensitive substrates
Cause
  • Deviating spray viscosity, spray technique, intermediate flash-off times and layer thicknesses
  • Spray gun (nozzle), spray pressure not correct
  • Paint material, substrate or room temperature too cool
  • Incorrect dilution or viscosity too low
  • Substrate has loosened
Avoidance
  • Processing according to manufacturer’s instructions
  • Use proper spraying equipment
  • Heat object and material to room temperature of 20 °C
  • Select good combination of hardener/thinner
Cause
  • Substrate not sufficiently dried out
  • Polyester materials not insulated
  • Pores not ground out
Avoidance
  • Allow starting materials to dry out well
  • Sand or fill pores well
Cause
  • Insufficient preparation of the substrate
  • Dust incidence
  • Unclean working equipment
Cause
  • Change of the substrate
  • Unsuitable coating system (lean on grease / primer on paint)
  • Incorrect pretreatment of the substrate
  • Layer thicknesses too high
Cause
  • Too thick layers if the surface dries too quickly
  • Swelling of coatings by water or solvents
  • Pull up (overpainting too early or too late especially with alkyd systems)
Cause
  • Sanding with too coarse sandpaper
  • Soft, elastic substrates
  • Top coat applied too thinly
Avoidance
  • Solvent test
  • Isolate the soft ground
  • Use specified abrasive paper
  • Apply normal layer thickness
Cause
  • Spray viscosity, spray pressure, spray technique
  • Spray gun, spray nozzle
  • Too short flash-off times
  • Unsuitable processing temperature
  • Unsuitable thinners
Avoidance
  • Observe processing instructions according to product information
  • Select suitable spray gun and spray nozzle
  • Guide the spray gun parallel to the object
  • Remain in the manufacturer’s product system
Cause
  • Climatic influences
  • Wrong hardener addition
  • Too thick layers
  • Insufficient substrate pre-treatment
  • Plasticiser migration
Cause
  • Unsuitable viscosity
  • Unsuitable solvents
  • Unfavorable temperature of the substrate and the coating material
Cause
  • Bleed-through of bitumen, organic pigments and dyes
  • Yellowing with phenolic coatings
  • Effects of light and industrial waste gases on pigments
  • Overburning with thermosetting coatings
Cause
  • Incorrect hardener
Avoidance
  • Observe data on product information
Cause
  • Deviating spray pressure, spray viscosity, spray technique, processing temperature
  • Unsuitable solvent combination
  • Scarred underground
  • Unsuitable spray gun (nozzle)
  • Too fast drying
  • Poorly flowing base coat
  • Absorbent substrate
  • Incorrect processing technique
  • No optimal layer thickness
Avoidance
  • Observe processing instructions according to product information
  • Proper surface preparation
  • Suitable spray gun (nozzle)
  • Use specified dilution
Cause
  • Layer thicknesses/ humidity
  • Substrate soluble
  • Curing error or hardener had already reacted with air humidity
  • Wrong dilution
  • Water or oil in the spray air
  • Drying interrupted
  • Sprayed too dry
Avoidance
  • Comply with the specifications on the product information
  • Closing hardener cans
  • Ensure sufficient fresh air supply
  • Do not interrupt forced drying
  • Observe drying time
  • Use correct dilution
Cause
  • Sanding water residues in corners, edges, folds and under trim strips
  • Spray air contaminated
  • Poor insulation of polyester products
  • Humidity too high
Avoidance
  • Always dismantle attachments if possible
  • Carefully blow out
  • Check oil and water separators regularly
Cause
  • Freshly painted, not yet cured coating
  • Layer thickness too high, drying time too short
  • Curing error or hardener no longer usable
  • Use of unsuitable dilution
Avoidance
  • Observe processing instructions according to product information
Cause
  • Condensation formation in fast-drying NC systems
Avoidance
  • Add retarder
Cause
  • Deviating spray viscosity, spray technique, flash-off times, spray room temperature
  • Spray gun, spray nozzle, spray pressure not correct
  • Unsuitable thinner
Avoidance
  • Set spray viscosity according to dipstick
  • Guide the spray gun parallel to the object
  • Select suitable spray gun and nozzle
  • Use thinner of the manufacturer
  • Observe processing instructions according to product information

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