There are small bubbles in my cured DiamondFinish Clear. How do I prevent this and fix it?

DiamondFinish Clear is a moisture-cured urethane. In some cases, small application issues can create tiny bubbles (micro-bubbles) in or on the clear film. The good news: the fixes are usually simple.

Micro-bubbles typically happen when thinner/reducer solvents become trapped inside the coating film. If the surface “skins over” too quickly, solvents can’t evaporate as intended. As they try to escape, they can leave bubbles, pinholes, or small craters.

Common causes of micro-bubbles:

• Not stirring properly before each use. Even though it’s a clear, it must be stirred gently and thoroughly before every coat. Touch the bottom of the can and lift repeatedly to disperse any settled resins/additives. Avoid violent shaking (shaking can introduce air). Don’t substitute shaking for stirring. Stir occasionally during use for the most uniform finish.
• Applying coats too heavy. DiamondFinish Clear should be applied in thin coats. Medium/heavy coats can skin over and trap solvent. Build film thickness with multiple thin coats—not heavy coats.
• Recoating too soon. If you apply the next coat before the previous coat has flashed/dried enough, solvents can become trapped. Recoat when the prior coat is dry-to-touch and does not leave a fingerprint—often within 2–4 hours depending on temperature and humidity.
• High humidity (above ~85% RH). Excess humidity can cause the surface to skin over faster and trap solvent. When humidity is high, either apply when conditions improve or reduce with KBS #1 Thinner or Xylene (about 10–30%) to slow/normalize flow and cure behavior.
• Trace moisture on the substrate. Moisture on the surface (especially porous substrates) can cause micro-bubbles. Dry the surface thoroughly before coating. Keep surface and air temperatures within a few degrees of each other, and ensure the surface temperature is at least 5°F above the dew point.
• Overworking the brush or roller. Rolling/brushing the same area repeatedly can accelerate skinning and cause micro-bubbles. Apply, lay it off, and move on—avoid going back over the same area over and over.

Simple fix:

Let the coating cure until sandpaper does not gum up, then sand smooth with 320 grit or finer and recoat. If needed for better flow-out, reduce the recoat 10–20% with KBS #1 Thinner or Xylene.