Paint failures or defects can occur due to various reasons, including poor or insufficient steelwork preparation, inadequate application techniques, or environmental factors. Here are some common paint failures and their causes:
- Insufficient Film Thickness: This occurs when the paint is not applied in the specified thickness. It can result from non-systematic application and inadequate checks with a wet film gauge.
- Sags/Runs: Sags or runs happen when the paint is applied too thickly or too much thinner is added. It can be due to not following the specification or occasional faults in the paint. Immediate repair with a brush is necessary.
- Dry Spraying: This occurs when the paint dries before reaching the surface, resulting in a rough and powdery texture. Poor application techniques or difficult weather conditions can contribute to dry spraying.
- Pinholes: Pinholes are small holes or voids that can occur on porous substrates. They are often found on zinc silicate surfaces and can be caused by applying a thick layer of paint or strong ventilation during application.
- Blistering: Blistering is a common adhesion-related problem that appears as raised bubbles on the paint surface. It can result from poor cleaning before application, particularly if the substrate is contaminated with salt. Osmotic blistering occurs in underwater or high-condensation areas.
- Rusting: Rusting occurs when a blister bursts, exposing the underlying unprotected metal to corrosion. It can happen in areas with thin paint film, such as sharp edges, rough welds, or difficult-to-access spots.
- Cracking: Cracks can appear after the aging of the coating and can be caused by factors such as a harder top coat than the layers underneath, excessive thickness combined with temperature variations, or fast curing of two-component systems. The excessive thickness of zinc silicate can result in “mud cracking.”
- Flaking: Flaking occurs when the paint film fails to adhere properly to the substrate. It can be a result of a poorly cleaned surface or applying paint over areas with blistering or cracking.
- Chalking: Chalking is an aging problem where the binder in the paint degrades due to UV radiation, leading to a powdery appearance on the surface. Different paint binders have varying resistance to chalking.
- Other Paint Defects: Other paint defects include wrinkling/lifting (small wrinkles in the paint film caused by skin drying or softening of previous coats), blooming (dull patches due to poor paint quality or inadequate ventilation), fading (gradual loss of color due to sunlight’s effect on pigments), flashing (presence of glossy patches caused by poor workmanship or paint quality), grinning (thin final coat revealing the background), and saponification (formation of soap patches due to the chemical action of alkalis).
Addressing these paint failures requires proper surface preparation, adherence to paint specifications, and using appropriate application techniques in suitable environmental conditions. Regular inspections and prompt repairs are important to maintain the integrity and performance of the paint system.