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Paint Peeling

August 1, 2011

 

Paint peeling is a very common problem and poor adhesion is the main reason behind this. The paint gets separated from the substrate leaving some paint behind.

Potential Reasons

  • Due to improper surface preparation,ie painting is done over surface which is wet,dirty or shiny.
  • Substrate had poor adhesion prior to being repainted.
  • Quality of the paint is low.

Paint Peeling in steel structures

In case of steel structures paint peeling mainly occurs due to improper surface preparation. De-lamination  occurs in the structure after paint-peeling. De-lamination refers to separation of layers from each other, of the structure which may be steel or iron and this leads to significant loss of mechanical toughness of the structure. It also leads to rust and corrosion of the material and decreases the life-time of the structure.

General Recommendation

After preparation of the surface for painting  the surface is subjected to environmental factors. The term “Hold the Blast” is commonly used and refers to the prevention of rust bloom from forming between the blasting and coating cycles. As a result general rules have been established which attempts to meet the specifications set by NACE and SSPC to maintain a 3°C differential between the air dew point and the surface to be painted,even an apparently dry surface before painting can later show major blistering and de-lamination problems. To avoid the  problem of peeling and de-lamination, dehumidifier can be used to remove moisture from the air at the surface, so that the air dew point is lowered sufficiently for the metal.

TDS Solution

TDS provides desiccant based dehumidifiers along with other accessories and technical manpower to provide the desired humidity level. The desiccant based dehumidifier removes moisture from the air by chemical attraction rather than condensation. Dehumidification is used 24 hours per day until all the blasting,painting and lining application is complete.

Dehumidifier takes moist air from outside environment, and feed dry air to the interior of the structure where coating is to be carried out. The dry air prevents condensation and high relative humidity at the surface.

Paint Peeling in concrete structures

Paint Peeling happens in concrete structures too. The main cause is improper surface preparation before painting. Most of the time painting is done over the concrete without completely drying it. Life & quality of painting gets hampered if it is done in the presence of high moisture levels, instead of adhering to the substrate i.e. concrete, the paint adheres to water, lowering its life. 

General Recommendation

Moisture level in the concrete should be maintained at 3-5%.

For steel structures 3°C differential between the air dew point and the surface to be painted needs to be kept.

TDS Solution

Drying i.e. reduction of moisture can be done with the help of dehumidifiers. Dehumidification is the most effective and quickest method of moisture removal. Dehumidification involves lowering the dew point of the air surrounding the steel structures and concrete so as the water starts to migrate  to the dry surrounding air. Dehumidification helps to achieve and maintain the desired level of moisture to prevent coating failure.

For inside coating of concrete floor/wall & pressure vessels dehumidified air can be fed through duct from the machine. In case of outside concrete painting in open atmosphere, a vapour barrier surrounding the job is created and dehumidified air is passed inside the vapour barrier through duct.

The desiccant based dehumidifier removes moisture from the air by chemical attraction rather than condensation. Humid air is directed across a desiccant material that acts as a drying agent. The moisture is collected in the desiccant. The moist desiccant is dried using second hot air stream that heats the desiccant and releases the moisture. Then the desiccant is reused to dry more air. In a continuous process the air is dried by the desiccant and at the same time the moist desiccant is dried for reuse so that dry air is available at all times continuously.

To provide the above parameters TDS provides a complete customized package solution of dehumidifiers,condensing units,blowers & ducts backed with technical manpower to maintain the required moisture(3%-5%) and temperature level.

 
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