Leveling (coatings)
- Also known as
- flow and leveling
Leveling is the ability of a wet coating to flow out after application and form a smooth, even film, eliminating brush marks, roller texture and other surface irregularities before it dries. It is driven by surface tension and opposed by the coating's viscosity.
What is leveling?
Applying paint with a brush, roller or spray gun leaves a surface that is not perfectly flat: brush marks, roller stipple or the texture of spray droplets. While the film is still wet, surface tension pulls the surface toward the smallest possible area, which means flattening those ridges. Good leveling lets that happen before the coating becomes too thick or dry to move.
What controls leveling
- Surface tension, which provides the driving force.
- Viscosity, which resists flow. Lower viscosity after application levels better.
- Time, the window before solvent or water loss and curing raise viscosity.
- Film thickness. Thicker films generally level more easily.
The trade-off with sagging
The same flow that levels a film can make it sag or run on vertical surfaces. Formulators use rheology modifiers so that viscosity recovers at a controlled rate after application: slow enough to level, fast enough to resist sagging.
Leveling additives
Flow and leveling additives, such as certain acrylic polymers, silicones and surfactants, even out surface tension differences across the film. Such differences can create defects such as orange peel, cratering and picture framing. Good pigment dispersion and substrate wetting also support a smooth film.
Frequently asked questions
A textured surface resembling the skin of an orange, a common leveling defect in sprayed coatings.
It lowers viscosity and can improve leveling, but it also increases the risk of sagging and can affect film thickness, hiding power and VOC content.
Sources
- Organic Coatings: Science and Technology, 4th edition, F. N. Jones, M. E. Nichols and S. P. Pappas, Wiley, 2017