Painting Defects

Settling

This is the separation of the pigments and occurs to a certain extent in all paints. It becomes a serious defect when the pigment is difficult to reincorporate into the paint by stirring.

The defect occurs due to the high densities of some pigments and can be accelerated by a drop in viscosity, the paint being stored at high ambient temperatures or by being subjected to vibration for example on long transportation by rail.

The control of settling lies in selection of suitable pigments and the addition of additives that increase the viscosity of the paint.

Slow Drying

Slow drying occurs when the paint remains tacky for an extended period of time. This will result in the film picking up insects or dirt before it is hard and will make repainting difficult.

The main causes are:

• Too thick of an application of the paint when using air-drying paints. As these paints require oxygen to penetrate the film to produce dying, if the film is too thick oxygen will not penetrate.
• The viscosity of the paint is too high for the application. This can occur in cold weather and can be overcome by reducing the viscosity with the recommended thinners for the paint.
• The paint was applied at too cold a temperature. This will cause the chemical reaction that takes place to cause the film to cure slowly.
• High humidity due to rain or the like will reduce the evaporation of the solvent, the first step in drying.
• The surface to which the paint is applied is not clean and has traces of wax or paint removed on it.
• The coat to which the paint is being applied has not dried when the next coat is applied.

Staining

Contamination of many surfaces with water, soot, smoke, tannins and tobacco can result in color coming through the paint surface to cause stains. Stains caused by water will leave a tide mark and after drying, the paint around the stain can be removed and the surface repainted. If the surface may become damp again, remove the source of the water or paint with chlorinated rubber or a hard varnish. Patches of soot or smoke should be removed before coating. Use of an insulating paint before the final coat can help. Nicotine should be removed with an alkaline cleaner (bleach) before coating. Remember to wash off all the alkali before attempting to paint.

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