Guangzhou Jinwei Chemical Co., Ltd

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Paint Defects Manual ( V )
- May 21, 2018 -

Paint Defects Manual (5)



21.Lifting / Solvent Aggression

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DEFINITION

Distortion or shriveling of the surface while the topcoat is being applied or drying.

CAUSES

[1]Incompatible materials. Solvents in the new topcoat attack the old surface, e.g., lacquer over enamel.

[2]Insufficient flash time or drying between coats.

[3]Improper surface cleaning or preparation.

[4]Wrong thinner or reducer.

HOW TO AVOID

[1]Use only materials that are compatible with the old surface, and designed for use with one another.

[2]Don't pile on topcoats. Allow sufficient flash and drying time. Topcoats should be applied when the previous coat is still soluble or after it has completely dried and is impervious to the topcoat solvents.

[3]Thoroughly clean the areas to be painted before and after sanding. Ensure the surface is completely dry before applying undercoats and topcoats.

[4]Use a thinner or reducer that is recommended for the topcoat being applied and is suitable for existing shop conditions.

HOW TO REPAIR

Remove the finish from the affected area and refinish.


22.Metamerism

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DEFINITION

Metamerism is the effect where a colour that appears the same shade to a second colour under certain conditions, may look totally different under different conditions. The most common existence of this problem is where two colours match in daylight, but appear different under artificial light (especially sodium street lighting).

CAUSES

Apart from the individual nature and the many variations of human colour perception, there a various other reasons for the occurrence of metamerism.

The pigment and/or base-colour composition of the repair paint does not correspond to the pigment composition of the original paint. 

The mixing of an unknown colour shade (where no mixing formula is available) without checking the shade under different light sources before use. 

By tinting a colour without reference to the base colours used in the colour formulation, i.e. tinting with a base colour which is not part of the original colour formulation.

HOW TO AVOID

For previous unknown colour shades, metamerism can only be avoided with the use of electronic colour measurement. For known shades (where a mixing formula is available), the shade must be checked under various light sources. Tint only with base colours which form part of the mixing formula and/or as specified in the tinting table.

HOW TO REPAIR

Slight variations in colour due to metamerism can be overcome by blending the colour into the surrounding panels. For severe metamerism, the colour shade must be re-mixed or reassessed by electronic colour measurement.


23.Orange-Peel Effect

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DEFINITION

Poor surface texture of the paint similar to the surface texture of an orange skin.

CAUSES

[1]Spray gun held too far from object. 

[2]Spray pressure too low (poor atomisation). 

[3]Paint film too thin. 

[4]Viscosity to high.(paint too thick). 

[5]Hardener and/or thinner too fast for the conditions or size of object. 

[6]Spray nozzle too small. 

[7]Flash-off time too long between coats.

HOW TO AVOID

[1]Keep spray gun within the recommended distance from the object. 

[2]Ensure spray pressure is as recommended. 

[3]Always apply wet coats. 

[4]Adjust paint viscosity as recommended. 

[5]Choose correct hardener and thinner (> temperature table). 

[6]See tech data for correct choice of spray nozzle. 

[7]Allow a long enough flash-off between coats.

HOW TO REPAIR

If the problem is only slight, sand down with P1200, polish with a fine polishing paste  and finish with a high gloss polish.


24.Poor Coverage

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DEFINITION

Substrate showing through the top-coat. Old paintwork, spot primer or areas of filler are visible through the top-coat.

CAUSES

[1]Substrate not coloured to similar even shade.

[2]Poor covering shade(e.g. no heavy metal pigment).

[3]Top-coat over-thinned.

[4]Top-coat not stirred properly before use.

[5]Paint coats were applied to thin.

HOW TO AVOID

[1]A uniform substrate is required, especially when using translucent colours(e.g. when using 3-coat pearl effect systems)

[2]For poor covering colours, use a tinting filler.

[3]Stir base colours thoroughly and always thin as per specification.

[4]Spray sufficient film thickness(solid colours 50-70 microns, Metallic basecoats 15-25 microns). Alternative for water-based colours: - spray a thin adhesion coat - blow dry - finish with 2 spray coats.

HOW TO REPAIR

After drying, sand down and repaint.


25.Pinhole Marks

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DEFINITION

Small holes or craters in the new paintwork as a result of solvent boil not removed properly from the substrate (old finish).

CAUSES

Solvent Boil or aeration of the old paint finish.

HOW TO AVOID

Either sand out the holes/craters completely or, where possible, fill the holes.

HOW TO REPAIR

Pinholes or small craters can only be repaired successfully by thorough sanding of the substrate or by filling the areas if practical or desirable.