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Paint Defects Manual ( II )
- Apr 16, 2018 -

Paint Defects Manual (2)


6.Chalking

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DEFINITION

Decomposition of the binding agents at the paint surface resulting in the release of the of the colour pigments. Reds and yellow colours turn whitish and dark blues turn bronze.

CAUSES

[1]Choice of wrong hardener or amount.

[2]Colour coats applied to thick.

[3]Weathering(aggressive environmental pollution such as sulphur dioxide and nitrous oxides in combination with high humidity and exposure to UV radiation).

[4]Poor after-care of the paintwork.

[5]Poor repair to a previously chalking paint finish.

HOW TO AVOID

[1]Always use recommended hardener and mixing ratio.

[2]Always keep to the recommended film thickness and number of coats. For colours with poor covering power (yellow’s reds etc), use a coloured surfacer (as used by OEM Automotive Industry).

[3]Regular paintwork maintenance.

[4]Ensure chalked paintwork is removed back to a “sound” substrate before refinishing.

Use base coat + clear lacquer system where possible.

HOW TO REPAIR

Try to polish out the problem using a fine polishing paste and finish with a high gloss polish. If the chalked surfaces do not respond to this action, or if the problem returns within a short period(a few weeks), then the damaged paintwork must be removed back to a “sound” substrate and refinished.


7.Cracking, Crazing

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DEFINITION

Cracks of various lengths and depths.

CAUSES

[1]Inappropriate paint system used on thermoplastic substrates (direct use of polyester body fillers/fillers, wash primers/synthetic resin products on TPA) which caused the TPA surface to soften.

[2]Refinished paintwork insufficiently cured (too little or no hardener used).

[3]Inappropriate paint system used:

Wash primer overcoated with polyester products.

Synthetic resin or nitro-cellulose paints overcoated too early.

[4]Cracks on plastic parts:

see chapter on "Faults in painting plastics".

[5]Exposure to strong UV radiation, extreme temperature fluctuations.

[6]Flash-off time too short in wet-on-wet process.

[7]Total film build too high.

HOW TO AVOID

[1]Apply a suitable paint system to the substrate.

[2]Ensure correct hardener quantities.

[3]Use correct paint system.

[4]Plasticise materials (see chapter "Faults in painting plastics").

[5]There are no complaints about "cracking" with regard to present Glasurit automotive refinish products.

[6]Respect recommended flash-off times.

[7]Check paint system and film thickness of old paintwork and sand down or strip down, if necessary.

HOW TO REPAIR

Sand down to the "sound" layers. Refinish using the recommended undercoats and topcoats.


8.Corrosion, Rust

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DEFINITION

Paint damage showing at the paint surface as irregular shaped blisters. If the blisters burst then corrosion spots are clearly visible (e.g. brown rust on steel or white rust on aluminium).

CAUSE

[1]Mechanical damage to the paint surface (e.g. stone chips, scratches etc.) causing penetration of moisture to the underlying coats or metal substrate. 

[2]Poor preparation of the metal prior to painting. Poor cleaning (see also chapter on "Blistering"). Poor rust removal or removal of metal particles from the metal surface.. 

[3]Flash rust formation on newly stripped or sand blasted metal surfaces.. 

[4]Inadequate or missing cavity sealing. (Rust through from behind).

HOW TO AVOID

[1]Stone chips or scratches should be repaired immediately. 

[2]Ensure through cleaning of all metal surfaces with an appropriate metal cleaner. Remove all rust by sand blasting to produce a bright metal substrate. Tin all welded seams. 

[3]Sandblasted areas should be primed immediately after blasting to avoid flash rusting 

[4]Seal and protect all cavities with the recommended products.

HOW TO REPAIR

Remove all paint and corrosion (rust) from the affected areas (by grinding, stripping, sandblasting). Thoroughly clean the area with an appropriate cleaner and wax and grease remover. Prime bare metal as quick as possible to avoid flash rusting and build up with the ecommended primers, surfacers and top-coats.


9.Clouding

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DEFINITION

Spots or stripes of light and dark patches, mainly seen in metallic finishes.

CAUSES

[1]Uneven spray application.

[2]Flash-off between coats or prior to application of clear coat too short. 

[3]Colour coat applied too heavy or too light.

HOW TO AVOID

[1]Application must be even and correctly overlapped with the previous gun stroke. 

[2]Ensure correct flash-off times are observed between coats. 

[3]Apply the basecoat as recommended in the technical information.

HOW TO REPAIR

If clouding occurs during the application of the basecoat, compensate by spraying over the affected areas using the correct technique. If clouding occurs after the clear lacquer has been applied, allow to dry, sand down, and repaint, using the correct technique.


10.Color Floating


DEFINITION

Because the granule size, shape, density and dispersion of pigments are different, the pigments in the top layer and under layer disperse unevenly, and there is color difference in different spray layer.

CAUSES 

Color floating relates closely with pigment convection during the formation process of paint finishes, thus incorrect manufacturing formula and technique are the main reason for this paint defect.

[1]In the manufacturing which needs more than two pigments, color floating occurs easily because solvent in the coating volatilizes differently.

[2]Excessive difference in density of different pigments.

[3]Dispersion of color paste could not reach requirement, incorrect dispersion method, or unsuitable dispersing machine.

[4]Lack of anti-floating agent.

[5]Low viscosity.

HOW TO REPAIR 

Re-spray with qualified paint over the defected paint finish.