Painting Defects

Viscosity Drop

Low viscosities may be simply due to incomplete stirring or the addition of too much solvent. The viscosity may decrease on standing in water-borne paints due to enzymic attack on the thickeners used. Modern latex paints use thickeners that are not readily attacked by bacteria. Changes in the orientation of the pigments (for example partial flocculation) may reduce the viscosity.

Wrinkling, Webbing, Frosting and Gas Checking

Wrinkling is the development of wrinkles in the paint film as it dries, usually due to the formation of a skin. Defects similar to wrinkling are webbing, frosting and gas checking. Webbing is the development of wrinkles, usually in a well defined pattern and if it occurs in an oven it is called gas checking. Frosting is the formation a haze which is due to fine wrinkles and it occurs in gas fired drying ovens.

The causes can be:

• Due to the paint's being applied too thick, especially with high oil-length alkyds, varnishes with wood oil and too much cobalt drier, enamels based on alkyd or phenolic resins with drying oils and black enamels containing bitumen.
• Stoving paints containing bitumen.
• Frosting may be due to the products combustion in the oven reacting with the surface of the film or may be due to high humidity.
• Too much cobalt drier.

Sometimes the wrinkle pattern may be induced into the paint to produce films that will hide surface defects.

Another type of defected related to wrinkling are crocodiling or alligatoring where the wrinkle pattern resembles the hide of one of these reptiles.

Posted in: BGAS Grade 3/2,BGAS Study Material,Frosting,Gas Checking,Painting Defect and Definition,Painting Defects,Viscosity Drop,Webbing,Wrinkling