Filtration requires a close look at the pigments used in a formulation. The type, shape, size and flexibility of the pigment varies widely, as do the percent solids, viscosity and rheological properties of the vehicle. Substrates may vary from a clean metal finish (automobile), to dirty steel (a bridge), to wood (home siding) and plastic. It is safe to say that proper filtration is key in producing a quality liquid coating, whether that coating be for homeowner architectural use or industrial or commercial applications including military specifications.
In addition, vehicles, both solventborne or waterborne, are film-formers. It is not unusual for skins of polymeric material to form in a drum or in a tank either during transportation/shipment or during storage (particularly if warehouse or outside/ambient conditions experience wide temperature swings). If skins get into a batch during grinding, mixing or thin-down operations, expensive filtration may be the only way to remove the material. Removal can be difficult because the particulates are soft, pliable and flexible, and easily clog any kind of filter, even if the filter is back-flushable.