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Ali Hamza
Ali Hamza
Mechanical
18 Jan 2019

What are the defects of painting??

Defects of Painting :

Cracking:

 Cracks extending throughout the thickness of paint are caused by improper seasoning of painted wood, excessive use of drier or application of too many coats resulting in an excessive thickness of paint. It results in scaling of paint.

Crazing and crocodiling:

 Use of too much oil, use of impure oil and insufficient drying of undercoat may cause hair cracks in top coat. If these hair cracks enclose small areas then the defect is known as crazing, however, if the areas enclosed are large then the defect is known a crocodiling.

Blistering and peeling:

Exposure of paints, rich in oil, to strong sunshine causes blisters. Blisters are also caused if oil or grease is left on surface to be painted. Painting a surface with moisture present on surface or in pores of wood causes peeling.

Runs and sage:

  Slow drying paint, painting over a glossy surface, use of excessive drier or excessive humidity and change of temperatures during drying period is the usual causes of the defect.

Chalking:

Use of insufficient oil in priming coat causes the paint to rub off with hands or clothes (the defect being known as chalking).

Washing off:

Use of pigments soluble in water causes the depo-sit of dissolved matter at lower edges forming streaks.

Dull appearance:

It is caused by use of excessive drier or on the paint becoming old.

Slow drying:

 Use of inferior or old oils, painting over damp surfaces or during unfavourable weather conditions causes this defect.

Yellowing of white paint:

 For indoor paintings where gloss is desired white enamel should be used otherwise minimum linseed oil, which has a yellow tint and does not bleach unless exposed to sun-shine should be used.