Water-based coatings vs. solvent-based coatings

Coatings frequently take their name from the binder, or resin, from which they’re made. Epoxies, alkyds and urethanes are all examples of resins that give a coating their name. But these aren’t the only parts that make up a coating. In addition to additives, which can lend a coating certain performance properties, and the pigments that lend color, coatings also contain an element that dissolves it all into a liquid for easy application.

This liquefying agent typically takes the form of water or some other chemical solvent. Hence the terms “water-based” and “solvent-based”. Which type of product is right for the job will depend on the circumstances. Generally speaking, one is not better than the other, but they do perform differently in different situations. Ideally, both options will exist side-by-side in a coating professional’s arsenal.

WATER-BASED COATINGS

Water-based paints make up about 80 percent of household paints sold today according to the Paint Quality Institute, a paint advising and testing organization. There’s no doubt this is in large part due to one of the main attractions of water-based products, whether it’s an interior house paint or heavy-duty protective coating: fewer odors.

When working in confined or poorly ventilated spaces, the evaporation of solvents can be uncomfortable for workers or even flat out hazardous to their health. For this reason, many projects like those involving fuel storage tanks and railroad tank cars make use of water-based coatings. These also reduce the concentration of flammable materials that build up in a confined space. That does not mean, however, that the use of water-based coatings negates the need for OSHA approved confined space safety measures.

Environmental compliance is another common reason for choosing to use a water-based coating. Many solvents evaporate into what are known as volatile organic compounds, or VOCs. National, state and local governments often regulate VOCs by limiting how much businesses are allowed to emit in a given timespan. The EPA sets national rules for VOCs, but some states have tightened restrictions even further, necessitating concerted efforts to limit their emission.

Water-based coatings don’t necessarily contain zero solvents, though. Many contain what are called co-solvents, solvents present in lower concentrations and meant to help push the rest of the water out of the coating as it dries. But since water-based coatings have either no, or considerably less solvents, they are a great way to lower a business’s VOC output. For some companies, this can mean spending less on environmental compliance advising. Or keep them from paying significant fines for exceeding VOC quotas.

SOLVENT-BASED COATINGS

Solvent-based paints are made up of liquefying agents that are meant to evaporate via a chemical reaction with oxygen. Typically, moving air surrounding a solvent-based coating will help to speed up the reaction, reducing drying times.

These coatings have one major advantage over water-based coatings. They are less susceptible to environmental conditions such as temperature and humidity during the curing phase. Humidity can actually prevent the water in a water-based coating from evaporating, making them impractical in some climates.

Water-based coatings also present a challenge to the surface prep stage of a coating project. Water, while a promising substitute for solvents in some situations, is also a key component of the corrosion process, the entire reason for the industrial coatings industry in the first place. If water makes contact with the substrate before the coating is applied, spot rusting may begin to occur. In order to ensure that this is not the case, water-based coatings must be formulated so that all the water is drawn out through the surface film before corrosion can occur. This is not a consideration with solvent-based coatings.

So, in summary, though water-based coatings may be a good option for jobs involving confined spaces and continuous coatings use, they’re not without their weak spots. Jobs in open, humid conditions, such as those often found in infrastructure recoating projects, can still benefit from the right coating. If you would like to discuss which type of product might be best for your project, we’d love to hear from you. 

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