If you’ve ever held a smooth, water-beading raincoat, a streak-free car paint job that repels water like magic, or a deck coating that sheds snow and moisture without cracking, you’ve encountered two key chemistry players at work: leveling agents and water repellency. As a leveling agent supplier, I field questions about this pairing all the time, and most of them boil down to a simple, often misunderstood question: How do these additives, designed to make coatings smooth and uniform, impact the very water-repelling property we might also be specifying? Let’s break this down from the lab bench, where my team tests these products daily, to the factory floor, where our customers apply them. Leveling Agent
First, let’s ground this in what each term actually means, because mixing up their core functions is where a lot of misinformation starts. Leveling agents are surface-active additives (surfactants, essentially) that reduce a coating’s surface tension, helping it flow evenly over a substrate, fill in tiny imperfections like brush strokes or pinholes, and form a continuous, uniform film instead of drying in uneven patches or beading up mid-application. Water repellency, on the other hand, is the ability of a coating to resist wetting, causing water to bead and roll off instead of spreading or absorbing into the film. The chemistry of these two seems almost opposing at first glance: surfactants lower surface tension, which sounds like it would make a coating more wettable, right? So why would a leveling agent ever improve water repellency, or when might it hurt it?
Let’s start with the good stuff—when leveling agents boost water repellency. I remember a call last year from a customer who makes marine anti-fouling coatings; he was complaining that his new, super water-repelling fluoropolymer coating was drying with so many fish eyes and brush marks that it failed his ISO 105-X12 scratch test. We recommended a modified polyacrylate leveling agent with a low hydrophilic-lipophilic balance (HLB, a scale that measures surfactant polarity), and he called me a week later saying his coating now flowed perfectly, had zero defects, and actually showed a 12% improvement in water contact angle (the standard measure of water repellency—higher angle = more repellent). That’s not a fluke, and here’s why it works.
When a coating dries, all its components—resins, pigments, additives—migrate to the air-coating interface as solvent evaporates, a process called surface segregation. Leveling agents with tailored chemistry can drive the right segregation here. The marine customer’s fluoropolymer has an extremely low surface energy (the core of its water repellency), but it’s a high-melt, high-viscosity resin that doesn’t flow well. The low-HLB polyacrylate leveling agent isn’t as low-energy as the fluoropolymer, but it’s miscible with the resin during wet application, so it doesn’t cause defects. As the coating cures, the leveling agent slowly migrates to the surface at a controlled rate, acting as a “bridge” that smooths out flow without disrupting the fluoropolymer’s ability to align at the top layer. The result? A continuous, uniform low-energy surface that doesn’t have the tiny gaps or uneven patches that would let water seep in. Without the leveling agent, the fluoropolymer couldn’t spread evenly, so there were tiny areas of higher surface energy (from the base resin or pigments) that dragged water down, lowering the contact angle.
Another example: exterior wood coatings. A lot of our customers use silicone-based leveling agents for these, because silicones are inherently low-energy. I once tested a clear acrylic wood coating that, without any additive, had a water contact angle of 82 degrees (pretty standard for acrylics) and began absorbing water into the wood after 72 hours of rain exposure. Adding a 0.3% concentration of a reactive silicone leveling agent—one that covalently bonds to the acrylic resin during cure, so it doesn’t leach out later—boosted the contact angle to 101 degrees, and the wood showed zero water absorption after 10 days of accelerated weathering. The key here is that the reactive silicone doesn’t just sit on the surface; it cures into the film, so it doesn’t rub off when you wipe the deck or get stepped on. That’s a big win because if a leveling agent is non-reactive, it can migrate too much over time, leaving bare spots on the surface.
But here’s the catch—leveling agents can kill water repellency if they’re not formulated right, and that’s the mistake a lot of newer formulators make. I worked with a small consumer paint brand two years ago that launched a “water-repellent interior/exterior paint” using a popular, generic polyether-modified polydimethylsiloxane (PDMS) leveling agent. Within three months, they were getting hundreds of complaints that rain beading was gone, and streaks were forming on siding. When we tested the failed batches, we found two issues: first, their generic leveling agent was too high in hydrophilic polyether groups, so it segregated to the surface first, creating a thin, polar layer that water adhered to. Second, they used too much of it—0.8% by weight, which is twice the recommended concentration. That’s a common error: adding more leveling agent doesn’t make the coating smoother; it creates excess surfactant that disrupts the low-energy surface.
Let’s get into the surface chemistry here to make this clear. Water repellency relies on the surface of the cured coating having a surface energy below 30 mN/m; anything above that will wet out easily. Most standard leveling agents have surface energies between 20 and 40 mN/m, depending on their chemistry. A high-energy leveling agent (like one with a lot of polyethylene oxide groups, which are hydrophilic) will never boost water repellency, because it’s pulling the surface energy up. Even a low-energy leveling agent (like a modified polyacrylate or reactive silicone) can cause problems if it’s not balanced. If too much is added, or if it’s too mobile during cure, it can create a thick, homogeneous layer at the surface that has a surface energy higher than the base coating’s low-energy resin. Or, worse, it can phase separate entirely—forming tiny, discrete islands on the surface that some areas are repellent and others are not, leading to uneven wetting.
Another critical factor is the type of coating system: water-based vs. solvent-based, 1K vs. 2K. I can’t tell you how many times a customer will use a leveling agent designed for solvent-based coatings in a water-based system, and wonder why their water repellency vanished. Water-based coatings have higher surface tension to begin with—around 72 mN/m, vs. 20-30 mN/m for solvent-based alkyds or urethanes. So the leveling agent needs to be matched to that system to reduce surface tension just enough to improve flow, without disrupting the water-repelling properties. For example, a water-based silicone leveling agent has to be emulsified to work in water, and the emulsifier is often a high-p H, hydrophilic surfactant. If the emulsifier doesn’t degrade during cure, it stays on the surface, making the coating more wettable. We solved that for one water-based exterior paint customer by developing a water-dispersible silicone leveling agent with a hydrolyzable emulsifier that breaks down during cure, leaving no polar residues on the surface—their contact angle went from 79 degrees to 98 degrees, and they had zero streaking.
Then there’s the role of leveling agents in preventing “dewetting,” which is the enemy of both smooth coatings and water repellency. Dewetting happens when a coating layer pulls back from the substrate, leaving tiny gaps. If that happens in a water-repelling coating, the gaps expose the substrate or base resin, which has a much higher surface energy. I tested a water-based fluoropolymer coating for a metal roofing application that was dewetting on galvanized steel, leading to rust spots and water pooling on the surface. Adding a small amount of our modified acrylic leveling agent reduced surface tension to match the substrate, so the coating wet out evenly, no gaps, and the fluoropolymer’s low-energy surface was continuous. The customer’s warranty for the roof went from 10 years to 20 after that change, and the water repellency test results showed no change after 5,000 hours of salt spray.
Wait, but what about anti-graffiti coatings? That’s a system where both leveling and water repellency are non-negotiable. Anti-graffiti coatings need to be smooth enough that spray paint can be wiped off easily, and they need to repel water so rain doesn’t seep under graffiti and make it harder to remove. A lot of formulators struggle here because traditional leveling agents can leave a residue that makes the coating more prone to graffiti sticking. We worked with an architectural coatings company on this, and we developed a hybrid leveling agent that combines the flow properties of a polyacrylate with the low surface energy of a silicone, but with a structured molecular design that doesn’t leave excess polar groups on the surface. The result: the coating had a water contact angle of 105 degrees, wiped away spray paint with just mild soap and water, and had zero brush marks or defects. That’s the sweet spot for many high-performance coatings—leveling agents that don’t trade one property for another, but enhance both when formulated correctly.
Another thing to consider is long-term durability, not just initial water repellency. A customer who makes packaging coatings told me that their initial water contact angle was great, but after being folded and creased for a few weeks, the repellency dropped by 30%. The issue was that their leveling agent was a non-reactive silicone that moved to the surface when the coating was flexed, leaving areas without the low-energy layer. We switched them to a crosslinkable silicone leveling agent that bonds to the polymer network during cure, so even when the coating is flexed, the low-energy groups stay locked in place. After six months of testing, their creased samples still had a contact angle of 97 degrees, vs. 72 degrees with the old leveling agent. That’s a common oversight: many formulators test water repellency right after application, not after the coating goes through its intended use stressors—flexing, UV exposure, abrasion. A good leveling agent has to maintain its balance over time, not just during the first 24 hours after cure.
So let’s sum this up, from the lessons my team and I have learned over thousands of formulating tests and customer projects. The relationship between leveling agents and water repellency isn’t a yes/no, it’s a matter of matching the right additive to the right coating system, at the right concentration, with the right chemistry. Low-HLB, reactive or crosslinkable leveling agents with tailored low surface energy will almost always boost water repellency by ensuring a continuous, uniform low-energy film forms, no defects, no gaps. Generic, high-hydrophilic leveling agents, or over-dosed additives, will disrupt the surface, pulling up surface energy and making water repellency drop. And the coating’s base chemistry, application method, and intended use all matter—what works for a marine anti-fouling coating won’t work for a water-based interior paint, no matter how good the additive is.
If you’re a formulator struggling with this balance—your coating is either too streaky or too bad at repelling water, or it works initially but fails over time—we can help. Our team has tested leveling agents for systems from exterior wood stains to industrial anti-graffiti coatings, and we can tailor an additive to your specific application, not just recommend a one-size-fits-all product. If you’re ready to work through your coating’s performance challenges and find a solution that gives you both the smooth finish you need and the water repellency your customers are asking for, reach out to our team to discuss your project details.
Weak Cationic Softener References
- Koleske, J. V. (2005). Surface Coatings: Science and Technology. John Wiley & Sons.
- Holmberg, K. (2001). Surfactants and Polymers in Aqueous Solution. John Wiley & Sons.
- Owens, D. K., & Wendt, R. C. (1969). Estimation of the surface free energy of polymers. Journal of Applied Polymer Science, 13(8), 1741-1747.
- Lambourne, R., & Strivens, T. A. (1999). Paint and Surface Coatings: Theory and Practice. Woodhead Publishing.
- Zhao, J., et al. (2018). The effect of leveling agents on the surface properties and performance of water-based fluoropolymer coatings. Progress in Organic Coatings, 123, 217-225.
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