Additives
Additional ingredients that affect and enhance many paint properties

Additives are ingredients which are used at low levels in paint formulations, but which play an important role in providing properties which a paint might otherwise lack. They are added during the manufacture of the paint, and not by the painter in the field. Below is a list of additives commonly used in waterborne acrylic paints, and a description of how they affect the properties of those paints:

THICKENERS AND RHEOLOGY MODIFIERS: rheology is the science of how a liquid tends to flow. Without thickeners, the prescribed amounts of pigment, binder and liquid would result in a mixture too thin to be practical for most applications. These additives provide adequate viscosity (thickness), so the paint may be applied properly. They impact how thick the paint goes on and how well it flows out when applied. Modern rheology modifiers help latex paints to:
- resist spattering when applied by roller
- flow out smoothly
- be less likely to spoil than those modified with older-generation thickeners (with spoilage, the paint may smell putrid and/or lose viscosity)
- resist sagging when applied in thick films

SURFACTANTS: specialized soaps, these additives help to stabilize the paint so that it will not separate or become too thick to use. They keep pigments dispersed for maximum gloss and hiding, and help :wet” the surface being painted so the paint won’t “crawl” when it is applied. They also provide compatibility with tinting colorants so that the correct color will be obtained, and help insure that it won’t change before the paint is used.

BIOCIDES: two types are generally used in waterborne acrylic coatings. The first is a preservative to keep bacteria from growing in the paint. This is especially important for paint stores in containers that are repeatedly opened and closed, because contamination can occur. The second is a mildewcide, to discourage mildew from growing on the surface of the paint after it has been applied. These are used mainly in exterior paints, although some interior paints, such as those formulated for use in damp areas (e.g., housepaints for kitchens and baths), may also contain mildewcide.

DEFOAMERS: These additives break bubbles as they are formed in the paint when:
- the paint is mixed in the factory
- it is put in a shaker or stirred
- it is applied to the surface (especially important when rolling or spraying the paint)

CO-SOLVENTS: are additional liquids other than water that are added to latex paints. One type is a coalescent, which aids the binder in forming a good film. It temporarily softens the acrylic binder particles so that they can fuse or coalesce, even when the paint is applied at its minimum recommended application temperature. Another type of co-solvent is added to help the liquid paint resist damage if frozen during storage. A third type of co-solvent is used to enhance application properties such as flow and “open time”. Open time is the time during which the paint can be applied and worked, before it sets up. Increased open time also helps in cutting back into a previously painted area when spraying, brushing or rolling large areas.

FLASH RUST ADDITIVES: are additives which inhibit the formation of rust while the waterborne paint is drying, also known as flash rust. Resistance to flash rust is especially important for waterborne primers or direct-to-metal (DTM) finishes, which are applied to bare steel or other ferrous surfaces. A properly formulated waterborne paint designed for application to ferrous substrates will not exhibit flash rusting, even under slow drying conditions such as high humidity, due to the presence of the flash rust additive.

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