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

DiamondFinish Clear is a moisture cured urethane and a few application issues can sometimes cause small bubbles (micro-bubbles) in or on the clear coating film. The good news is the application tweaks to fix this issue are small, simple, and easy.

The cause of the small bubbles is solvent (thinner/reducer) becomes "trapped" in the coating film when the surface layer skins over too quickly and this prevents their evaporation into the atmosphere which is part of the normal curing process for coatings. Solvents that vaporize within the paint film (because they are unable to escape as intended) leave bubbles, pinholes, or craters as they push through and "pop" the surface.

Here are common causes of small (micro) bubbles in the DiamondFinish Clear coating film.

  • Lack of proper stirring before each time DiamondFinish Clear is applied. Some think that because DiamondFinish Clear is a clear coating that it does not have to be stirred. But, just like all coatings, DiamondFinish Clear must be stirred well before each coat/application so the coating can adhere to the substrate and cure properly giving the desired finish. Before each use, stir DiamondFinish Clear gently and thoroughly. Proper stirring is very important for the best uniform sheen and finish. Effective stirring includes repeatedly touching bottom of can and lifting to disperse any settled resins or additives. Avoid violent or excessive shaking motions which produce air bubbles that will adversely affect the finish. Do not substitute shaking for stirring. For the best end results, continue to stir often during the course of use.
  • Too heavy of a coat applied. DiamondFinish Clear must be applied in thin coats only. If a medium or heavy coat is applied, solvent entrapment can happen as the outermost part skins over causing solvent entrapment. Apply DiamondFinish Clear in thin coats only. You can apply several coats to create a desired film thickness, but this must be done with many thin coats and not with heavy or medium coats.
  • Not enough time between coats. If a subsequent coat of DiamondFinish Clear is applied too soon, micro-bubbling can occur as the solvents from the previous coat try to evaporate but are now trapped. Re-coating can be done once the first or consecutive coat is dry-to-touch and does not leave a fingerprint which is typically within 2-4 hours depending very much on temperature and humidity.
  • Excess humidity in the air can cause DiamondFinish Clear to skin over too quickly causing micro-bubbles. When humidity is high (above 85RH), you can slow the cure by adding KBS #1 Thinner or Xylene (10-30%) or do the application when the humidity is not so high.
  • Trace moisture on the surface to be coated can cause micro-bubbles. Always dry the surface really well before you apply DiamondFinish Clear. This is especially a key on porous substrates. Always make sure the surface and air temperature are with a few degrees of each other. The surface temperature should be at least 5F above the dew point temperature.
  • Overworking the roller or brush. If the brush or roller is overworked when applying DiamondFinish Clear, this can cause the DiamondFinish Clear to cure too quickly forcing a skin over layer which then can cause micro-bubbles. It is always best to roll or brush an area with DiamondFinish Clear and move on immediately versus rolling or brushing an area over and over again.

To simply fix the issue, sand smooth with 320 or finer grit sand paper, and then recoat. Wait to sand until DiamondFinish Clear has cured enough that the sandpaper does not gum up when sanding. When you recoat with DiamondFinish Clear, you can thin or reduce 10-20% with KBS #1 Thinner or Xylene to help flow out (relieve surface tension) when needed.