Content area
Full Text
Painting a bridge or an industrial structure is an expensive operation. Now more than ever, state DOTs and facility owners are specifying warranties and application methods to ensure the longest possible life for their coatings. Determining what factors affect paint cure can help to achieve the optimum performance and provide the owner and contractor with fewer headaches down the road. As always, for any coating to be successful, a good specification, quality contractor, proper equipment and of course an effective inspection program are all necessary components.
Once paint is applied we need to wait a specified period of time to let the paint pass from a liquid state to a solid state. This is commonly known as drying time.
Contractors, coating inspectors and owners speak of drying, hardening and curing of a coating, but it is important to clarify each of these coating states as they mean different things and occur at different times in the process.
Drying to the Touch for Solventand Water-Based Coatings
The paint-drying process corresponds to the evaporation of all solvents and diluents added to the paint in order to make it a liquid. Paint "dry" happens when the solvents evaporate from the coating, leaving the paint feeling dry to the touch even though it is not 100-percent cured. Drying time is sensitive to temperature and humidity. For most coatings, to be "dry to the touch" is not a sufficient state over which to apply another coat. Product data sheets must be consulted to ensure proper application.
Hardening (Dry to Recoat)
The hardening of a coating corresponds to the process by which the main polymer of the coating hardens with all the other pigments and additives that make up the paint, creating a solid and adherent coating. Hardening does not necessarily mean curing. Hardening is, however, most often the state at which recoat is acceptable.
Cure (Complete Cure)
The paint-curing process corresponds to both the drying and the hardening processes. For example, a coating can be dry to the touch 30 minutes after application but not hardened enough to recoat until...