What Does Recoat Window Mean?
A recoat window is the time period during which a subsequent coat of enamel paint may be applied. It indicates the allowable time frame in which a successive coat must be applied to ensure a strong chemical bond of the two coats.
Any coat applied outside the recoat window without additional surface preparation may not adhere sufficiently to the first coat and results in low-quality coating incapable of providing protection against corrosion.
Corrosionpedia Explains Recoat Window
The recoat window refers to the period that begins from the point at which the coat of paint has cured enough to be topcoated, and then to the point at which the coat has hardened in a way that additional coating cannot adhere sufficiently.
Coating within the window allows the previous coat to cure enough to support the subsequent coat without sagging, while enabling the two coats to bond strongly to one another. As the coating cures further and beyond the recoat window, its ability to react with successive coats diminishes.
If coating outside the recoat window, additional surface preparation such as the application of a bond coat, or mechanical abrading, is necessary to allow for proper mechanical bonding.
Problems associated with painting outside the recoat windows include poor performance such as the inability to protect against corrosion, fish eyes, poor adhesion, and premature failures. The manufacturers may include procedures required when coating outside the recommended window.
The recoat window is influenced by the film thickness, type of paint, substrate, and ambient conditions such as humidity, temperature, and air flow. It usually shortens at high temperatures and humidity.
The recoat window ranges from a few minutes to 24 hours for fast curing, to several days or weeks for multi-day applications, while some paints have indefinite recoat windows.
The epoxy primer for some applications such as in the field, construction sites, and shops requires variable recoat windows. This provides flexibility for projects in which the completion dates cannot be specified due to distribution logistics, construction schedules, and environmental factors.
Other areas where a variable recoat window is desired are:
- Marine applications
- Paper mills
- Storage tanks
- Power plants
A longer recoat window is sometimes beneficial for applications that need recoating after millage repairs, holiday repair, or multi-day applications.