Guangzhou Jinwei Chemical Co., Ltd

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Paint Defects Manual ( VI )
- May 26, 2018 -

Paint Defects Manual (6)



26.Polishing Marks

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DEFINITION

Very fine lines in the paint surface with a low gloss greyish appearance from polishing paste and/or cloth.

CAUSES

[1]The sensitivity of the paint surface to polishing marks is greater when: the paint has not been allowed to dry for long enough; the film thickness is too high; the incorrect choice or amount of hardener has been used. 

[2]Excessive pressure has been exerted on the polishing machine, (polish burnt in).  

[3]Polishing machine tilted during polishing process.

[4]Wrong polishing head. 

[5]Aggressive/coarse polishing paste. 

[6]Polishing when the painted surface is too hot from the oven or in direct sun light.

HOW TO AVOID

[1]Ensure only the correct film thickness, drying times and choice of hardener and thinner are observed. Before polishing, allow the paint layers to dry sufficiently (rebake using Infra Red if necessary). 

[2]Do not press too hard or tilt the polishing head and use the correct head for the application being carried out. 

[3]Do not use too coarse a polishing paste. 6] Ensure that the paint surface is cool and/or not in the sun.

HOW TO REPAIR

Polish out the problem with any standard deep gloss polish. If the problem is more severe, first use a fine polishing paste.


27.Poor DOI


DEFINITION

Distincness of Image (DOI) refers definition of paint film's projection, which is closely related to the smoothness and gloss of paint film. It is one exterior decoration performance of paint film. Poor opacity means bad decoration performance. DOI can be visible or quantized by special test equipment.

CAUSES

[1]Coarse substrate, rough sanding paper or not fine enough sanding.

[2]Paint applied runs vertically, lack of gloss, fails in fineness and opacity.

[3]Bad spray booth condition lead particles existing on the top and lack of gloss.

[4]Bad atomization cause serious orange peel.

[5]Insufficient thickness makes lack of saturation.

HOW TO REPAIR

If after sanding and polishing, it is still ineffective, then should choose another refinish system with better DOI to apply.


28.Poor Drying


DEFINITION

The paint film could not dry thoroughly after normal necessary time and requires an extra long drying period, or fails to harden thoroughly.

CAUSES

[1]Incorrect mixing ratio of 2K paint (too much or less of hardener).

[2]Unsuitable hardener.

[3]The temperature could not reach requirement.

Normally speaking, when the temperature is lower than 10℃, the drying process would be excessively slow.

[4]Over-thickness of the paint film.

[5]Poor weather condition and poor ventilation.

[6]Insufficient, bad quality or wrong thinner.

[7]Incorrect application method.

HOW TO REPAIR

[1]Increase the drying temperature to make the paint film dry thoroughly.

[2]If the paint film could not dry thoroughly even by increasing the temperature, sand or remove the paint, then re-spray.


29.Paint Mist,Dry Spray


DEFINITION

In the spray process, paint mists drop on the paint finish and make the paint finish rough, full of small particles and loss of gloss.

CAUSES

[1]Incorrect spray method: Spray gun too far away from the surface, not vertical to the surface, spray speed too fast, or air pressure too high.

[2]Incorrect viscosity; thinner too fast.

[3]Too near to the surface and easily affected by the paint mist.

[4]Poor ventilation of the spray room.

[5]No covering of the part unnecessary for application.

[6]Dirty or damaged spray gun.

HOW TO REPAIR

[1]Primer: Allow it dry, then sand.

[2]Topcoat: Fine sand the last layer of dry spray, then polish.

[3]Single layer silver basecoat: Sand and re-spray.


30.Putty Patch or Substrate Scratches


DEFINITION

During the paint drying process, paint finish loses gloss and the under layer defects like putty patches and substrate scratches could be seen easily.

CAUSES

[1]Wrong size of sanding paper and poor sanding.

[2]Substrate dry spray.

[3]Insufficient flash-off time between layers.

[4]Poor drying condition.

[5]Primer is sanded when it is not thoroughly drying.

[6]Uneven stirring of the primer.

[7]Poor solubility of thinner.

HOW TO REPAIR

[1]For small defect, after thoroughly drying, fine sand, then polish.

[2]In serious cases, after thoroughly drying, fine sand, then re-spray.