The paint droplets must blend together on the surface of the part and form a
smooth layer with a uniform thickness. Premature evaporation of the solvent
during spraying must therefore be prevented, otherwise an effect called "dry
spray" may occur. The climatic conditions, like temperature and humidity,
should be well-controlled for a good, reproducible coating result. An
undesirable temperature rise during hot days can lead to the dry spray effect.
The paint can also be applied with a brush (stripe painting), a roller, a
resilient pad (decorative figures), by dipping or by dyeing (fibers and
fabrics). A mask can be used if the surface of a part is only partially to be
covered with paint. The painting process can also be integrated with the
injection molding process in several ways, avoiding the need for a
separate painting line.
Foam molded parts cannot be painted immediately after molding. The gases
produced by the foaming agents must first reach equilibrium with the ambient
air. This outgassing may require 24 to 48 hours, depending on temperature and
humidity. Painting before this equilibrium is reached may cause blistering.