When a waterborne wood coating is brushed on, the brush marks still level out on their own during the first ten minutes or so, but after about half an hour they set, leaving a series of ridges when the surface is sanded. Workshops habitually add leveling agent to the paint; add too much and the film becomes slippery and recoat adhesion drops, while the brush marks stay exactly the same. For brush marks to form, two conditions must hold at once: the coating has not finished leveling within the given time, and the driving force for leveling is not enough to smooth out the grooves left by the brush. A waterborne system has a shorter open time than a solventborne one; water evaporates quickly and thixotropic recovery is also fast, so the paint enters a non-flowing state before it has spread out.
Whether the Brush Marks Are Uniform or Localized Tells You the Cause Differs
Uniform brush marks across the whole panel usually mean the open time is too short: the film sets soon after brushing, which is closely tied to the application environment and the paint's viscosity. Localized heavy brush marks with more pronounced edges commonly point to uneven substrate absorption, where dense wood grain takes in paint quickly and the film dries locally first. When a film shows both craters and brush marks, the surface tension is out of balance; at that point adding leveling agent may only create more craters, and the first thing to check is where the contamination comes from.
Order of Handling: Adjust Application Conditions First, Then Check the Substrate, and Only Then Touch the Leveling Agent
First adjust application viscosity and the application environment. When the temperature is high and the draft is strong, water escapes quickly; lowering the solids content slightly or shortening the interval between coats can buy time. Then check substrate sealing: unsealed wood takes in paint quickly, so applying a sealing primer first creates room for leveling. Only then turn to the leveling agent, starting below the recommended value and observing how much the brush marks improve. If doubling the dosage brings no improvement, the bottleneck is not in the leveling agent.
Selection Points: Look at Dynamic Surface Tension and Compatibility Together
In a waterborne system, it is not enough for the leveling agent to lower static surface tension; what decides how fast the film spreads is dynamic surface tension, and volatile types and reactive types differ greatly. Then look at compatibility: poor compatibility with the resin leads to exudation, haze and craters. Third, look at the effect on hand feel and recoatability: a high silicone content gives a slippery feel, but used too much it reduces intercoat adhesion.
Chemitech's Solution
For waterborne wood coatings, industrial coatings and architectural coatings, Chemitech offers silicone-based, acrylic-based and polyurethane-based leveling agents that can be used in brushing, roller coating and spraying.
Compared with silicone types, acrylic types have less effect on intercoat adhesion and are better suited to applications that require recoating; polyurethane types have good hydrophilicity in waterborne systems and a broader compatibility range with waterborne resins; silicone types improve craters and orange peel more directly, but demand tighter control of dosage. The three differ noticeably in slip and recoatability.
A coating's open time is decided by the resin system and application conditions; a leveling agent can only improve spreading within a limited window, and expecting it to extend that window is unrealistic. The specific match has to be judged in light of the system conditions.
Once the resin system, application method and environmental conditions are described to our technical team, we can give a product direction and support it with sample validation. Waterborne Leveling Agent Solutions and Coating Orange Peel and Crater Solutions are worth a look first.
Summary
Brush marks in waterborne wood coatings mostly come down to neglected open time and substrate sealing; the leveling agent cannot be blamed for everything. Controlling the temperature and humidity of the application environment, sealing the substrate well, and only then adjusting the type and dosage of the leveling agent is what makes improvement reliable. When selecting a product, put dynamic surface tension and compatibility first, and avoid high-silicone types where recoating requirements are high. Chemitech offers three leveling agent lines for waterborne systems, silicone, acrylic and polyurethane, which can be matched to the resin and application method. If you have a formulation list, our engineers can go through it with you at any time.