Additives can change the working properties of a coating or to add a special feature by simply stirring it into the product. Some are simple dispersants while others may react with the chemicals that constitute the paint film. Since all of these alter the formulation, manufacturer defect warranties may be compromised and care must be taken on the part of the consumer to ensure that the additive and the paint can be used together. A paint manufacturer like Coronado that supplies additives will have tested their products for compatibility. Other generically similar products may work well with a particular additive, but not necessarily.
Testing is recommended prior to full-scale use to determine if there are any negative effects.
Unusual aromas, increased brittleness, a change in opacity, decreased spread rates, induced pot life, and difficult brushing are all possible side effects from use of certain additives. Over adding may also create its own share of problems. A variety of additives should be a part of every painter's toolbox. Paints are made and tested in a controlled laboratory setting but are applied in the real world where environmental conditions change day to day. The label might say that paint X is good for both metal and wood, however, the same paint applied on a metal door during a windy hot dry day will seem like an entirely different product on the wood trim in a damp, cool restaurant.