Q: Can waterborne acrylic coatings be used on steel?
A: Absolutely. A common perception is that if a waterborne coating is applied to clean steel, the result will be rust. Although steel will rust in the presence of water, oxygen and electrolyte (salt), waterborne acrylic industrial coatings designed for coating metal are formulated to inhibit the rusting of the steel surface while the paint is drying. On the other hand, waterborne paints not designed for coating steel, such as exterior house paints, can lead to rusting known as flash rust. However, industrial waterborne acrylics have been used successfully on steel and other metal surfaces for 40 years in both field and factory settings.

Q: What is flash rusting and how can it be prevented?
A: Flash rusting is signaled by the presence of small rust spots on the paint film, or sometimes by a tarnishing of larger areas, and usually appears shortly after application and before the coating is dry to touch. It generally results from slow drying conditions, especially at high humidity, and is caused by the migration of corrosion products through the paint film. It generally does not affect long term performance, but detracts from the coating’s appearance. Flash rusting can be eliminated through proper formulation of the waterborne acrylic coating. Inorganic salts such as sodium nitrite are typically added as flash rust inhibitors. Avoiding application under extremely high humidities is also recommended.

Q: Can I thin my waterborne industrial paint with water to make it flow or spray better?
A: Waterborne paints are designed to be applied at the supplied viscosity, and thinning should not be necessary. If thinning is required, use only clean water and use it sparingly. Excessive thinning will result in sagging, reduced film build, and possibly performance problems. Always follow the manufacturer’s recommendations.

Q: Are waterborne acrylic coatings useful for immersion service?
A: While waterborne acrylic coatings can be successfully used in many aggressive industrial environments, they are not recommended for immersion service. Some waterborne acrylics, such as those used for roof coatings, can withstand periods of contact with pooled water, but they are not suitable for permanent immersion.

Q: Why aren’t all waterborne coatings considered zero VOC (volatile organic content)?
A: Although they are more environmentally-friendly alternatives compared to many solventborne coatings, most waterborne acrylic coatings do contain some volatile organic compounds, and thus are not zero VOC. The organic compounds often enter the paint formulation from co-solvents called coalescents, which are necessary to soften the acrylic polymer particles so that they can fuse together as the film dries. Many additives such as defoamers, pigment dispersants and wetting agents also contribute low levels of volatile organic compounds.

Q: What types of waterborne acrylic coatings are commercially available for use on steel?
A: There are a number of different types of industrial coatings available that are based on waterborne acrylics. Anti-corrosive primers designed for direct application to prepared steel surfaces are usually formulated with inhibitive pigments to aid in long term corrosion protection. Topcoats are available in a range of sheen from flat to high gloss. A special class of coatings that are designed to act as both the primer and finish coat are also available, as designated as DTM (direct-to-metal) coatings. Elastomeric coatings are formulated to be applied as surface-tolerant, thick film coatings which provide corrosion protection and flexibility. Waterborne acrylic wash primers are meant to act as a thin film tie-coats between substrates that are difficult for adhesion (such as galvanized) and successive coats. Two-component coatings based on acrylic/epoxy crosslinked systems are used for both industrial maintenance and interior institutional coatings, where greater chemical resistance is required.

Q: What is the temperature and humidity range normally recommended with waterborne acrylic coatings?
A: The best temperature range for use of waterborne acrylics is between about 60 °F and 90°F, although painting at temperatures as low as 45°F can be done. Most manufacturers recommend temperature ranges of about 45 to 110°F. Painting at very high relative humidity (>90%) can lead to significantly slower drying times. Usually it is recommended to paint when the humidity is less than 85-90%, and the temperature is at least 5 degrees above the dew point to prevent condensation. Painting under conditions outside of the manufacturer’s recommendations can lead to problems with film formation and eventually performance. Click here for more information on this topic.

Q: How long does a waterborne coating have to dry before it can be recoated?
A: If applied within the recommended temperature and humidity ranges, most waterborne acrylic coatings will dry and can be recoated within 4 to 8 hours.