Paint delamination and debonding refer to the separation of one coating layer from another, known as inter-coat adhesion failure, or the separation of the coating from its underlying surface, termed substrate adhesion failure. This issue arises from various causes, with inadequate surface preparation and prolonged exposure to corrosive environments, such as seawater, being the most common culprits.
Errors during the coating process led to the debonding of paint layers, exposing the substrate and causing the steel to oxidize.
Additionally, delamination can occur when the substrate material itself becomes compromised. For instance, in roofing sheets, the stress from drilling and fixings can weaken the coating and substrate, causing them to separate. This separation reduces mechanical strength, leading to splits in the protective coating. If these splits are left unprotected, water ingress can occur, resulting in corrosion.
In this post, we will focus on paint blistering caused by loss of adhesion and cathodic delamination. But first, let’s clarify the distinction between debonding and delamination.
Steel cladding that is suffering from severe debonding due to contamination during re-coating carried out by non-approved paint contractors.
Delamination and debonding
Delamination – occurs when a laminated material, often a coating or other composite, separates into layers due to impact or other factors. This failure can manifest as fractures within the adhesive or resin, within the reinforcement, or as detachment of the resin from the reinforcement.
Debonding – happens when an adhesive ceases to adhere to a substrate material. The adhesive could be an organic polymer or an inorganic coating. Debonding occurs when the physical, chemical, or mechanical forces maintaining the bond are disrupted, possibly due to external force, contamination during coating process or environmental factors.
Blistering is caused by contaminants between layers and failure to properly prepare the cladding for re-coating.
Paint blistering delamination
Paint blistering results from the loss of adhesion or debonding between coats. This issue is primarily caused by contamination between layers, exceeding recommended overcoat times, or applying paint to a glossy surface. To prevent blistering, keep the area clean and free from contaminants, adhere to the manufacturer’s recommended intervals between coats, and sufficiently abrade glossy surfaces before applying the next layer.
Paint blistering delamination de-adhesion and debonding.
Cathodic delamination
Cathodic delamination refers to the separation of a coating from its substrate at a defect site in a corrosive environment. This typically occurs when an electrochemical reaction produces hydroxide ions between the coating and the metal substrate, leading to the weakening or loss of adhesion. Common in seawater-immersed organic coatings and areas exposed to corrosive material, this process can create osmotic pressure, causing blisters and further separation of the two elements.
Cathodic Delamination
What surfaces are affected?
Paint delamination can affect the protective coatings of any substrate from concrete and timber to steel and aluminum. Paint delamination takes place on floors, roofs, pipelines, guttering, in fact anywhere the requires a protective coating. Whether its occurring on a concrete floor or steel roof sheet, the process happens for generally the same reasons.
Delamination on pipelines caused by inadequate cleaning prior to coating.
How to prevent paint coating delamination
Like any coating process its all about preparation and the quality of the product. Whether you’re applying a protective coating system to metal cladding or a concrete floor, its important to get some key things right.
Choose a quality coating system
The same rule applies to protective coatings as it does for any other product, buy cheap, pay twice! Don’t be governed by the price. If you buy a cheap paint system it won’t last as long as a good quality product. For example here at D&D Coatings we use only the highest quality coating products by the most reputable manufacturers for all our projects. You don’t want a situation where in twelves months or less, you have to redo all the work that should have lasted years.
Good preparation
When applying paint directly to a substrate or over an existing coating, proper procedures must be followed. Strip the old coating using abrasive blasting to create a suitable profile on the steel substrate. Ensure the exposed area is dry, clean, and free from dust and contaminants. This preparation is crucial for the base coat to adhere properly and prevent catastrophic adhesion failure. Any dirt, oil, dust, or grease on the surface can hinder optimal adhesion of the coating.
Don’t work when its too hot or too cold
It might sound obvious but its a common mistake made by many. Don’t apply coatings when its too hot, or when its too cold. Painting on a hot surface forces the solvent out of the coating too quickly resulting poor adherence. When the surface is too cold, condensation can develop making the steel substrate vulnerable to flash rusting and corrosion settling in. It can also affect the properties of the paint and weaken the bond between the substrate and the coating.
