What Is Causing Bubbles or Blisters in My Polyurea/Hybrid Coating?

Once you’ve applied a fresh layer of polyurea or hybrid coating to a surface, the last thing you want to see are bubbles or blisters. Whether they appear in one spot or are seen throughout the entire coating, they are typically caused by the same thing: trapped air. Bubbling occurs when pockets form beneath the coating, which causes the coating to lift and create that bubbled appearance. Bubbles not only ruin the coating’s appearance but also result in adhesion failure.

Reasons Polyurea/Hybrid Coatings Bubble

Reason #1: Poor Surface Preparation

Option 1: Proper surface preparation is key to avoiding bubbling. When bubbles form, it is typically because contamination on the surface creates a barrier and prevents the coating from adhering. Rather than sticking to the surface, the coating will adhere to dust, debris, oils, etc., that are present. Once the coating has cured, over time it will blister and delaminate from the surface.

Option 2: Apart from an unclean surface, bubbles can also occur if the surface isn’t prepared in other ways. Some surfaces, to generate adhesion, will need to be abraded. This is typically done by sanding, shot blasting, or abrasive blasting to a certain degree. If the proper surface profile is not created, you will notice bubbling issues over time.

Option 3: Some surfaces will create more bubbling problems for coatings than others. If you are working over a porous surface, you need to make sure moisture is not trapped before applying the coating. When a coating is applied without proper surface prep, moisture will become sealed underneath. If the surface is subject to high temperatures that increase pressure, the only place for that moisture to go is up toward the coated surface, causing a blister.

Reason #2: Incorrect Mix Ratio

While mixing issues aren’t typically a problem for high-pressure spray coatings, sometimes the spray equipment can become off-ratio. If sprayed at the wrong mix ratio, it might be gummy and cause adhesion issues. This gumminess can indicate that too much of one component was used. While polyurea isn’t as sensitive to moisture as hybrids, it can be affected by being off ratio and will cause bubbles. An off-ratio issue will usually only occur due to incorrect equipment setup or required maintenance.

Another potential off-ratio issue can occur when using cartridge-based spray equipment. It’s important to start spraying off the surface you want to coat first. It takes a few seconds for the coating to mix thoroughly in the static mix tip. If you immediately start spraying the cartridge on your designated surface, you might notice bubbles in the coating once it has cured. If you are using the VFI Qwik Spray System, check out our how-to-use blog here for more tips.

Reason #3: Temperature Issues

If you’re working in extreme temperatures, whether it’s hot or cold, they can affect the way your coating cures, causing bubbling or pinholes. Applying a coating in direct sunlight or high heat will cause the coating to cure rapidly, which will accelerate the cure and may cause adhesion issues, which will make a blister. On the alternative, if you’re applying in colder temperatures, it slows the coating’s ability to cure, which can also leave room for more bubbles to form with uncured or partially cured material.

Reason #4: Moisture Issues

Polyurea coatings typically will not have moisture issues due to their insensitivity. However, while the moisture wouldn’t necessarily react with a polyurea, the coating wouldn’t be able to properly adhere to a wet surface. This lack of adhesion would generate blisters.

There are a few ways moisture can cause bubbling in hybrid coatings. If there is moisture on or in the surface, in the atmosphere, or within spray lines, bubbles can occur.

• Surface moisture. If you do not properly dry the surface before applying the coating, the coating will react and bubble. Some porous surfaces also contain moisture, which can create bubbling if that moisture flows to the surface from extreme temperature changes.
• Spray equipment moisture. If moisture from the air gets into spray lines, it can cause bubbling in the coating because the isocyanate component will react with the moisture. Isocyanate will create CO2 and start to foam, which is how these pinholes appear once sprayed.
• Humidity. If you’re working in an environment with relatively high humidity, the moisture in the air can react with the coating after it’s sprayed and while it’s curing.

Solutions

The best way to avoid bubbles or blisters after applying a polyurea or hybrid coating is by following the manufacturer’s instructions. Double-check your equipment to ensure it’s proportioning the correct mix ratio before spraying.

If possible, work in a temperature-controlled environment. The best application temperature for most polyurea and hybrid coatings is between 65-100°F. Avoid coating in direct sunlight, high humidity, or rain to minimize moisture-related issues.

Performing a moisture vapor test on porous surfaces that may contain moisture is also recommended. Thoroughly clean and dry your application surface before coating to prevent adhesion issues. The method of cleaning you use will depend on the type and level of contamination on your surface. This includes solvent cleaning, power washing, or mechanical cleaning.

Another important step for porous surfaces is applying a primer. This can create a barrier that helps prevent trapped air and moisture from reaching the coating to cause bubbles. Primer not only seals the surface but also promotes better adhesion between the surface and the coating, which also prevents delamination. The surface should be coated as soon as possible after preparation to avoid further contamination.

Some blisters can be repaired by identifying the cause, removing them from the surface, preparing the surrounding area, applying a primer, and reapplying the coating.

Contact VFI if you have other issues with your polyurea or hybrid coating. Our technical team is available to help troubleshoot and find solutions to your problems.