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Technology Tips from the Paint Lab: Understanding and Dealing with Blistering Headaches

A D+D Online Feature published December 13 2010

by V.C. “Bud” Jenkins
	Large blisters will form on solvent-borne acrylic coatings, especially low-VOC coatings, on a cold, clear morning. Where do they come from? What causes them?... (Login to read the full article)

Comment from Michael EDISON, (12/14/2010, 9:14 AM)

This is a very useful, practical article. One point I would question is in regard to VOC reduction by use of Acetone (or other VOC-exempt solvents). Since the VOC-exempt solvent is deducted from both the numerator as a weight per unit volume and from the donominator as a volume %, it doesn't seem like these exempt solvents offer much VOC reduction from a regulatory point of view. Am I missing something? What would be typical VOC-compliant combinations of acetone and xylene/aromatic 100 in a solvent-borne acrylic coating?

Comment from V. Jenkins, (12/14/2010, 11:07 AM)

The reason that using Acetone or PCBTF as an exempt solvent is to get the viscosity down without causing smog. It works to get the viscosity down, but then the formulator has to put up with the side effects such as fast evaporation in the case of acetone or high cost in the case of PCBTF. There has been a movement among the regulators to change the rules to grams of voc per pound of applied paint solids. That way there would be true VOC reduction when paints are applied. In a solution acrylic, 25 to 50% of the solvent weight might be acetone. Formulators will generally put in as much of the slower evaporation voc as they can in order to get the paint to flow out, but the Acetone helps get the paint onto the roller or out of the gun.

Comment from John Fauth, (11/19/2012, 8:35 AM)

I think the industry understands there is no single cause of bubble formation in acrylic sealers. There certainly is a correlation between exempt oxygenated solvents (such as acetone, tertiarybutyl acetate and dimethyl carbonate) and bubble formation as described in the article. But to single out acetone as the culprit just isn't accurate. I think this phenomena is more common on warm days (rather than cool mornings), and there's no doubt that solar energy plays a part as well. As does outgassing from capillary pores as the concrete substrate warms and air expands. That's more likely the cause of bubble formation on cool mornings the author describes. Other causes of bubble formation in low-VOC coatings include entrapped air from vigorous roller application, over application due to several factors (fast solvent evaporation raises solids content resulting in heavier DFT, use of sealer to knock down bubbles or cob webbing increases WFT, etc) and a host of other factors that do not impact traditional aromatic solvents (xylene, aromatic 100, etc) in the same way.

Comment from VCBud Jenkins, (11/19/2012, 11:40 AM)

I would like to respond to John Fauth's comment that there is no single cause of bubble formation. I agree, but the emphasis of my article is to show that vapors get trapped below the surface of the film when the sunlight warms and hardens the surface. Whether the vapors come from the trapped xylene or the outgassing from the concrete pores is not as material as the fact that they do get trapped and cause a bubble to form. I have seen these bubbles grow in front of me like a balloon. We have had more problems such as these since we have been using acetone as a primary solvent in low VOC sealers which is why I mentioned acetone. Blisters can happen for other reasons but the faster evaporating solvents are one important reason that they happen.

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