Management

Fleet Group Management

- Chalking of Paint and its effect on weather decks By Pradeep Nair & Luis Aranha

What is Chalking

Chalking is defined as... “The appearance of a loosely adherent fine powder on the surface of a paint film, arising from the degradation of one or more of its constituents.

Chalking is a fine, powdery white substance that forms on painted exteriors, chalking is most often seen in sunny climates & is normally caused by exposure to UV light. The rate of degradation will vary depending on the topcoat color, environmental conditions and the type of paint used.

Some chalking is to be expected as all paints will be affected by UV radiation to some degree, over time, particularly on weather decks. However, after a while, the decks will have dull appearance giving an impression of poor maintenance.

White or colored powdery chalking residue

Factors causing chalking

Sunlight and ultraviolet (UV) radiation:

Chalking occurs more quickly in exterior environments where the painted surface is fully exposed to high levels of sunlight over an extended period. Surfaces protected from direct sunlight will deteriorate at a much slower rate. Also, the intensity of the solar radiation will affect the degree of chalking. Radiation from sunlight interacting with the constituents within the paint film breaks down the bond between molecules in the coating film. Over time UV degradation of the binder or resin within the paint film will allow the exposed pigment particles to become more loosely bound to the surface. The result is a powdery surface. It is most common in epoxy coatings but can be seen in almost all coatings left exposed to causative conditions for a long enough period.

Hot/cold temperature cycling: Greater the extremes of UV radiation and temperature, greater the stress on the coating system.

Application of darker colored paint:

Darker colors absorb more energy (heat and UV radiation) from sunlight than lighter colors thereby putting greater stress on paint coating. High UV intensity and greater energy absorption will result in more deterioration of the paint surface. Also, chalking is visually more obvious on darker colors.

Marine environments:

The combination of salt and atmospheric moisture creates a corrosive environment and constant exposure will cause coatings to start showing signs of deterioration more quickly than otherwise might be expected.

Correct film thickness: Product application at lower than the recommended film build can accelerate the overall ageing process of the coating system, resulting in premature deterioration. If chalking occurs prematurely or non-uniformly, this is often a sign that there may have been some inconsistencies during application, resulting in fluctuations in the applied film build, leaving some areas more vulnerable to early degradation.

Wrong product: Using a paint that is designed primarily for interior use, on an exterior application. Epoxy resin coatings, in the absence of a suitable topcoat, will undergo yellowing and chalking on exterior exposure.

Detrimental effects of chalking:

 Lightens the color of the paint, giving the surface a dull appearance  Erode the paint film, resulting in a loss of protection  Run down onto the underlying structure and deface the appearance of the surface

Chalking observed on fleet vessels

Degradation due to the “chalking” is irreversible once it begins to occur and the appearance can often become quite irregular or patchy in appearance. To eliminate the effect completely, the entire surface will need to be pressure washed and/or scrubbed with a non-metallic scouring pad to remove all surface contaminants and chalking prior to repainting with an approved UV resistant coating system.

Minimizing/Avoiding chalking onboard

Sigmacover 350 expoxy paint is not ideal for topcoat for Sun/weather exposed deck areas, using it as a finish coat can result in chalking and discoloration giving a poor cosmetic appearance of the deck condition. Recoating with Sigmacover 350 at short intervals to reduce the chalking can be also challenging for the crew, given that surface preparation is more delicate for epoxy primers, and the area has to be roughened entirely (sand papered) and then High pressure washed to remove chalky residues.

Polyurethane Sigmadur 550 (Glossy) has greater resistance to Chalking and has been used on some vessels with good lasting results. Polyurethane will not suffer from breakdown in terms of UV light exposure compared to epoxy. Recoating Sigmadur 550 will be at much longer intervals and surface preparation is much simpler as it can be overcoated without roughening of surfaces.

Vessels in consultation with the technical superintendent should evaluate using Polyurethane Sigmadur 550 (Glossy) and update the maintenance chart onboard if it is not mentioning Chalking Free Topcoat on main deck areas.