How to Achieve an Incredible Looking Finish When Applying A Moisture Cured Paint

How to Achieve an Incredible Looking Finish When Applying A Moisture Cured Paint

You just applied the final coat of a moisture cured paint or coating. It’s still wet and so far, everything looks great. You call it a job well done and leave the piece to dry thoroughly. Later you come back to inspect your work and see micro bubbles have formed in the coating. Ugh! Now you must either deal with it the way it is, or sand down the bubbles and apply another coat. Keep in mind, user error is the main reason why moisture cured paints and coatings form bubbles, and it can be easily avoided.

What is a Moisture Cured Paint or Coating?

A moisture cured paint or coating is a type of coating which cures in the presence of atmospheric moisture. It forms a protective film by reacting chemically with the moisture in the air. Moisture cured paints and coatings are a one-part (1K) formulation and include clearcoats, such as DiamondFinish Clear, Rust preventative coatings, like RustSeal, BlackTop, and KBS MAXX, as well as other paints, coatings, and sealants. Among the benefits of moisture cured paints and coatings is that they withstand pooling water, produce a hard, durable, and highly reflective surface, and have good adhesion characteristics. Moisture cured coatings are popular for use in humid environments as the humidity can help rather than hinder curing, as it can with paints and coatings that aren’t moisture cured. However, excessive humidity can cause problems with the curing of moisture cured coatings, which we’ll talk about a little later.

Moisture cured paints and coatings are made up of pigments, additives, resins and solvents. Since they cure in the presence of water vapor, their formulation is solvent based, rather than water based. The solvent functions to dissolve or disperse a variety of components used in the formulation. As the paint or coating begins to dry the solvent evaporates and the resin component remains to create a hard coating that is not breathable. This advanced coatings technology helps to resist stains, contaminants, and rust.

Why Moisture Cured Paints and Coatings Can Form Bubbles

That brings us to those nasty little bubbles in the paint or coating you may have found after it dried. The bubbles are typically formed because of gas and vapor pressures within the paint or coating. This typically happens when a coat of product is applied too thick and a film, or skin, forms over the top of the still wet and solvent rich paint or coating. Much like pudding that has skinned over. The solvent gas in the wet coating has difficulty evaporating through the film and becomes trapped. Known as Solvent Entrapment, the condition forms bubbles under the skin. Blistering can also occur with moisture cured paints or coatings. This is different than bubbling and can happen when they are applied during high humidity, or on wet surfaces, meaning a wet on wet application.

The resulting bubbles eventually dry in place as the paint cures. This not only looks bad but can compromise the protection the paint or coating is intended to provide; a hard, non-breathable film that seals the material it is applied to away from moisture, oxygen, and contaminants. The bubbles can cause the coating to form a permeable Swiss cheese like structure which can allow these elements to pass through.

Tips for Applying Moisture Cured Coatings

  • Avoiding paint bubbles is a matter of taking care and being patient. Instead of applying a couple of thick coats of product to get the job done quickly, time should be taken to apply it in multiple thin coats. With each coat being given sufficient time to dry and off-gas solvent. For example, with RustSeal, KBS recommends applying an additional coat once the first or consecutive coat is dry-to-the-touch and does not leave a fingerprint, which is typically within 2-6 hours depending on temperature and humidity. Applying an additional coat on top of that which has not had sufficient cure time is a sure-fire way to make the paint or coating bubble up.
  • Remember to not apply moisture cured products in rainy, excessively humid conditions, or on wet surfaces.
  • When brushing or rolling on moisture cured coatings it’s important to not “overwork” the brush or roller. Continually going back and forth over the paint or coating forces out the solvent gases at a faster rate than that intended by the manufacturer for proper self-leveling and curing.

In Summary

User error is the main reason why moisture cured paints and coatings can form bubbles. However, by being patient and taking care to not apply coats too thickly and allowing sufficient dry time between coats it can be avoided.