Polyurea coating has been called a revolutionary chemistry that can be applied down to -35˚ F and withstand water exposure almost immediately. As good as the technology is, however, the truth is that no coating chemistry can make up for an improperly prepared surface. Ask anyone in the industry, and they’ll tell you that most failures are a direct result of poor surface preparation.
In fact, in its infancy, polyurea was promoted as the coating that would cure on any substrate. But many early polyurea jobs failed because the coating cured without sticking to the substrate. The result was a catastrophic adhesion failure for the job and a public relations problem for the polyurea industry. The performance properties of a coating system don’t eliminate the need for the user to ensure that the coating system has something structurally sound and clean to which to adhere.
If a surface is contaminated with oil, for example, the oil must be removed. The substrate must not only have a surface or anchor profile to get good mechanical adhesion, but also have a level of cleanliness appropriate to the application and end use. Beware of the salesperson who tries to convince you that the product is tough enough to make up for an inadequately prepared anchor profile.
Also known as surface profile, the anchor profile is the topography of the surface to be coated. If the anchor profile left by the surface preparation is too smooth, it allows for coating slippage, or creep, when the coating is exposed to lateral pressure. So be sure that there is an appropriate level of roughness for the coating to fill. The level of anchor profile required depends on the coating system used, the choice of primers, and other considerations that the specifier should consider. The graphic visually demonstrates the anchor profile.
Ask questions and get answers that make sense ahead of time to avoid having to backpedal and investigate a job failure later. Polyurea coating technology is coating chemistry. Protect yourself with the facts. At the end of the day, you are the one to whom your customer will either give, or not give, repeat business and referrals. It’s your reputation on the line.
Cross-link density refers to the way polymer threads are woven together and the density or packing of those threads. The higher the cross-link density, the better the barrier-type properties of a coating system.
An example illustrating the cross-link densities of two different polyurea coating system formulas is chain link fence vs. chain mail armor. Both are made of metal, are woven together, and offer a certain level of protection. If a circus performer were to throw an ax at you, you could feel equally confident of your safety by standing behind either a section of chain link fence or a section of chain mail armor. In both cases, the molecule size of the ax cannot penetrate the cross-link density of your formula. However, if that same circus performer were to throw a razor-sharp 7” balanced knife at you, you would probably not feel the same level of confidence standing behind the fence as you would the armor. Why? Because the cross-link density of the armor doesn’t allow the small molecule knife to pass through. Which would you choose for protection, the chain mail or the chain link fence?
In comparing Polyurea coating systems, cross-link densities are not all the same. Although similar, the end results, and the level of protection offered, can be very different from one formula to another. By design, coatings with no solvents or volatile organic compounds (VOCs) of any kind (listed, exempt, or other) have the capacity of exhibiting the highest cross-link density.
Don’t be deceived or misled. The use of any solvent in a coating system is both a performance and safety concern. Look for materials which are designed for the specific needs of your project
The original definition of a Volatile Organic Compound (VOC) was any organic compound with a vapor pressure higher than 0.1 millimeter of mercury, allowing it to enter the atmosphere quickly and easily. VOCs typically lower the viscosity, or thickness, of the coating chemicals and enable the chemicals to be more easily sprayed. Most solvents meet the original definition of a VOC–entering the atmosphere quickly and easily–but not all solvents are VOCs, something not commonly known
An exempt solvent is a solvent compound that by all characteristics is a VOC according to the original definition but has been exempted from the law for some reason. Unscrupulous coating suppliers can incorporate either non-VOC solvents or even exempt solvents into their formulated products. By definition, they now have a non-VOC product. Some companies will sell a product labeled as Zero VOC that contains non-VOC solvent, but never disclose that information on the label. Zero VOCs does not mean no solvents, and the product label may not tell the whole story.
By using a non-VOC solvent to disperse the resins, formulators can use much cheaper resin raw materials. On the other hand, true 100% solids resin materials, while more expensive, have a low enough viscosity to be cold sprayed without the use of any type of recognized solvent. Beware of the phrases Zero VOCs or No VOCs. They do not automatically mean solvent-free or no solvents.
Investigate further into whether a coating, in fact, has no solvents, versus only no VOCs, by learning more about some of the solvents defined as “exempt solvents” in the United States. These include: Acetone, Methyl Acetate, Volatile methyl siloxanes, Parachlorobenzotrifluoride (PCBTF), Methylene chloride, and a wide range of chlorofluorocarbons. You may find these listed either on a side panel of the packaging or on the Material Data Safety Sheet (MSDS). When you request a MSDS from the product manufacturer, it should always be made available to you. Some manufacturers provide this information on their websites