Painting not only gives a good appearance to a structure but also provides protection against various infiltrative actions such as corrosion, decaying, weathering, etc. But however, paint film also gets deteriorated by these actions. Hence the paint should be selected based on many factors such as type of surface, type of environment, etc. Otherwise, defects may occur in painting. Some of the common defects that usually occur in painting works are explained in this article.
Defects in Painting
Following are the common defects that occur in painting :
- Blistering and Peeling
1. Blistering and Peeling
Blistering and peeling are defects in which swelling of the paint film occurs. The swelling is caused by the formation of an air bubble under the paint film due to the presence of moisture or oil or grease matter. If it is due to moisture then it is called peeling and if it is due to oil and grease matter then it is called blistering.
Blistering and peeling occur due to the imperfect seasoning of timber, usage of excess oil in final coat, imprisoned gases between paint coats, etc. These defects can be eliminated by using porous paints like emulsion paints instead of non-porous paints such as oil paints, enamel paints, etc.
Fading is the discoloration of the paint surface. This is mainly due to atmospheric agencies such as sunlight, moisture, etc. To prevent fading or discoloration, weathering resistant pigments should be used in the paint.
The paint film should be opaque enough to cover the background surface. The visibility of background due to insufficient opacity of paint film even after the final coat is called as grinning.
Chalking is the formation of powder on the painted surface. This is due to the use of insufficient oil in the primer. It can be prevented by using sufficient oil in the primer, applying paint at recommended spreading rate, etc.
When a thin layer of paint is coating on a glossy and smooth surface the paint may run back and sometimes leaves small areas of surface uncovered. This defect is called running.
When a surface is to be painted with a thick layer of paint, the thick paint film may run downwards and forms sagging of paint. It is similar to running but here the sag of paint is very thick.
The detachment of paint film from the surface is called flaking. It occurs when the bond between surface and paint film is poor. To prevent this, the surface should be cleaned and rubbed with abrasive paper before applying paint.
Blooming is the defect caused due to improper ventilation, weathering, defective paint, etc. In this case, dull patches are formed on the painted surface.
Wrinkling occurs when a thick layer of paint is to be coated on the surface. In this case, the paint film gets shrinks and develops crawls on the surface as shown in the picture. It can be prevented by allowing the undercoat to dry completely prior to the application of the final coat.
The formation of glossy patches on the painted surface is called flashing. This is caused due to the poor quality of paint, weathering action, poor workmanship, etc.
Saponification of paints occurred when the painted surface is exposed to chemicals such as alkalis. In this defect, soap patches are formed on the paint surface and paint film gets peeled off from the surface.
Alligatoring is pattern cracking similar to the scales of an alligator. It occurs when the hard coat of paint is applied over the soft coat or existing coat of paint. To prevent this, a high-quality oil-based primer should be used as a prime coat.
It is similar to alligatoring but here cracks are limited to a small area, unlike alligatoring cracks. It is caused when the paint is applied during very cold weather or due to the application of paint prior to drying of undercoat.
Mildew is a form of fungus which grows well in warm, moist and dark places. It grows rapidly and develops the grey colored patches on the painted surface. It also affects the bond between paint coats. It can be prevented by keeping the surface dry and clean before applying paint. If there is any trace of mildew growth, then wash the surface with the solution of bleach.