Guangzhou Jinwei Chemical Co., Ltd

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Paint Defects Manual ( IV )
- May 12, 2018 -

Paint Defects Manual (4)



16.Faults in Painting Plastic - Pinhole

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DEFINITION

Small holes in the paint surface due to pores and bubbles in the plastic. This problem often appears on the soft flexible parts (e.g. PUR rear spoilers) and GRP fibre-glass mouldings.

CAUSES

Expansion faults or foam holes in the plastics from production.

HOW TO AVOID

Thoroughly check the plastic part for pores before painting and where necessary use the pore filler wiping process.

HOW TO REPAIR

Porous paintwork can, in principal, be repaired using the pore filler wiping process(sand down, porewipe, refinish).

Note: Too many pores in the plastic will make it very difficult to paint. It is important to check the plastic for pores thoroughly before painting.


17.Fading


DEFINITION

Color pigments changed after exposure to prolonged sunlight.

CAUSES

[1]Inferior paint used for refinishing.

[2]Repeated exposure to strong sunlight or corrosive atmosphere or contamination.

[3]Use improper hardener which lower the properties of the paint film.

HOW TO AVOID

[1]Use quality paint for refinishing.

[2]Protect the vehicle from bright sunlight when not in use.

[3]Keep vehicle clean and well maintained.

[4]Use recommended hardener per technical data sheet.

HOW TO REPAIR

Sand and repaint.


18.Industrial Fallout

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DEFINITION

Spots of corrosion on top of the paint surface.

CAUSES

Industrial Dust Corrosive deposits from chimneys of foundries and ironworks. Rail and road chippings. Iron particles, which mainly occur on top flat surfaces, oxidise in moisture and humidity and then attack the paint surfaces. Spark Damage Ash from overheated electricity cables on tramways and railways. Spark damage from welding and grinding operations. The hot and sometimes glowing, particles of iron burn into the paint surface.

HOW TO AVOID

Immediate removal of the metal particles and regular maintenance by polishing and waxing will help to avoid the problem. Where welding or grinding work is being carried out, ensure that all vehicles adjacent to or near the work are fully covered to protect them.

HOW TO REPAIR

Use a metal dust remover and finish off by polishing the surface with a polishing paste. If the metal particles are deeply etched into the pain surface, sand down the affected areas with P1200 and then polish with a polishing paste.


19.Loss of Gloss/Matting

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DEFINITION

Matt or matted paint surface.

CAUSES

[1]Paint swelling.

[2]Excessive film thicknesses.

[3]Weathering (results of the action of sulphur dioxide or nitrous oxide combined with moisture and/or severe UV radiation).

[4]Wrong amount of hardener.

[5]Poor or incorrect paintwork care:

(1)Incorrect polishing (polish too aggressive, or polished in direct sunlight).

(2)Weathered surfaces due to poor aftercare maintenance.

(3)Car wash brushes too coarse.

(4)Car cleaning agent too aggressive or concentrated. 

[6]Newly repaired paintwork weathered too early. Thick coats or newly repaired paintwork are [7]sensitive to condensation (below dew point).

Insufficient air circulation during drying.

HOW TO AVOID

(1)See chapter on “Swelling”.

(2)Always keep to the film builds as recommended. With poor covering top coats (yellow and reds) use a tinting surfacer.

(3)Ensure regular paintwork aftercare.

(4)Keep to recommended mixing ratios.

(5)See chapter on “Aftercare of vehicle paintwork”.

(6)Keep to recommended film thicknesses and drying times.

(7)Check air circulation, replace floor and ceiling filters if necessary. If in doubt, consult your spraybooth manufacturer.

HOW TO REPAIR

Try to polish out the problem with a polishing paste, and finish with a high gloss polish.

If the gloss cannot be restored, then remove back to a sound substrate and refinish.


20.Loss of Adhesion

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DEFINITION

Loss of adhesion can manifest itself in 2 different ways. First – where a total lack of adhesion occurs below the entire paint film. Second – where a lack of adhesion occurs between coats.

CAUSES

Loss of adhesion can occur when:

[1]Substances which can cause adhesion failure are left on the substrate (e.g. silicon, oil, grease, wax, rust, sanding residue, etc.) 

[2]An unsuitable primer or surfacer was applied to the substrate.  

[3]Insufficient sanding was carried out to the substrate. 

[4]Primer or base coats were applied too dry or too thin. 

[5]Poor drying conditions.

HOW TO AVOID

To avoid the result of loss of adhesion to the substrate, always use the correct type of primer and/or surfacer for the substrate (e.g. for aluminium, steel or plastic etc.). Only apply primers as per specification (see Technical Data Sheets or Tech Data on the cans.) Do not apply coats too thick. Thoroughly clean the substrate before application of paint materials.

HOW TO REPAIR

Remove all coats with poor adhesion. Thoroughly sand and clean the substrate. Repaint using the correct choice of primer and/or surfacer and/or top-coats.