Low-VOC paints dry faster, have less open time, and less flow and leveling. That's why it's important that painters be aware of the limitations these products have and adjust their techniques accordingly.
by Susan Brimo-Cox
Such is the case with low-VOC paints, because making the switch from traditional paints to low-VOC paints is not as simple as it may seem.
If you’re a professional painting contractor in California, Arizona or another area of the country where low-VOC coatings have been the norm for several years, you may wonder what all the fuss is about. But if you’re painting in the Northeast or Mid-Atlantic region — where the change-over is still relatively recent — you may still be bristling with frustration as you refine your old painting techniques to adapt to the subtle, yet significant, challenges these coatings offer up.
And if you haven’t had to make the switch yet, just wait. Your time will come. Several Midwestern states (Ohio, Indiana, Illinois, Michigan and Wisconsin, for example) are currently considering adopting low-VOC regulations similar to those in Northeast and Mid-Atlantic states.
Nigel Costolloe, president of Catchlight Inc. Fine Residential Painting, expects the laws to eventually be adopted nationwide “since air pollution does not recognize state lines and manufacturers will not want to produce two kinds of products.”
What’s the big deal? The VOCs: volatile organic compounds. While VOCs are found in both latex and oil-based paints, there are less of them, obviously, in low-VOC coatings. Therein lay the difficulties.
Low-VOC formulas contain less solvent and a different type of emulsion. “An emulsion with a low Minimum Film Formulation Temperature (MFFT) is necessary,” reports Jim Armstrong, senior lab manager at Rodda Paint Co.
These differences may seem small, but they mean low-VOC paints handle and perform differently.
Dan Greenwell, Duron Architectural Product Specialist, explains that with both low-VOC latex and oil-based paint it is more difficult to keep a wet edge while you are applying the paint. Flow and leveling characteristics of these products also is lessened, and they will want to setup more quickly.
Armstrong echoes the observations that low-VOC paints dry faster, have less open time, and less flow and leveling. That’s why it is important, he says, that painters be aware of the limitations these products have and adjust their techniques accordingly.
Another area of concern, reports Shashi Patel, executive vice president at Muralo Co., is with block resistance, which is less in low-VOC paints than with traditional paints if they are not formulated properly.
Armstrong points out that low MFFT is not well suited for developing block resistance. But, he agrees, too, “there are ways to mitigate the problem through formulation.” Still, he adds, a solvent-free coating will not achieve the block resistance of a traditional, solvent-containing acrylic trim enamel.
Bruce Schneider, end-user marketing manager at Purdy, observes low-VOC coatings “generally don’t have the adhesion of traditional alkyds when applied over grimy, chalky, peeling surfaces.”
And when it comes to cleanup, Greenwell recommends using both soap and water for low-VOC latex paints, whereas just water was usually sufficient in the past. Low-VOC oil-based paints, he says, clean up about the same as traditional formulas.
There are practical approaches to painting with low-VOC paints that minimize potential problems presented by the rapid drying characteristics of these products.
Armstrong says that when “cutting in” a room you need to work in smaller increments and roll in as soon as possible. And he shares a tip: “If painting in warm, dry conditions, placing a humidifier in the room will help slow down the dry time.”
Greenwell also emphasizes that speed is critical and points out that painters working with low-VOC paints learn quickly to just apply the paint and move on. “You can’t continue to brush ‘back and forth’ or roll ‘up and down’ for an extended period, perhaps as you once did with more traditional paint.”
And don’t forget the basics. As Costolloe points out, “Brushing skills are important; brushing from dry into wet, feathering the finish stroke and brushing with the grain.”
As you would expect, using a quality brush improves the results. And when working with low-VOC paints, as with traditional paints, choose a synthetic bristle brush for latex or water-based formulas and natural bristles for oil-based products. But what about bristle count, brush stiffness and other characteristics?
Greenwell observes that paintbrushes with a greater number of bristles hold more paint and require less dipping. This helps you keep moving, since your wet-edge time is reduced.
According to Patel, because low-VOC paints generally contain higher solids, a slightly stiffer brush will work better to spread paint around.
Schneider points out that some brush manufacturers have developed stiffer brushes that push through heavier paints more easily. Purdy started making Pro-Extra brushes about five years ago specifically for low-VOC paints.
On the other hand, Glen Wiseman, Wooster district manager of Ohio and West Virginia, says that low-VOC products go on easier and look better if you use a softer, finer bristle. For solvent-borne paints, he recommends white China bristle or an ox hair/China bristle blend. “Although black China bristle has long been a favorite of professionals, white bristle and ox hair are softer and finer than black bristle and will do a better job with high solids.”
For low-VOC acrylic coatings, Wiseman says a top-quality, 100 percent nylon brush offers the benefit of faster, more thorough cleaning than a nylon/polyester blend.
The rules don’t really change much for low-VOC paints when it comes to rolling them on. Most experts agree that you need to choose roller nap based on the smoothness or roughness of the surface being painted and the sheen of the finish, not whether you’re using a traditional or low-VOC paint.
John Dee, owner of John W. Dee Painting & Decorating, says with rollers it comes down to productivity versus leveling. “High nap always carried more paint, but can result in a linear roller pattern.”
As with brushing on, you need to work quickly. This minimizes any roller stippling.
But Wiseman says to be careful with lamb’s wool rollers. “For low-VOC coatings, a lamb’s wool 1⁄2-inch or 3⁄4-inch cover would cause mud-cracking because too much product is being applied.”
He also says to steer clear of paint pads. For one thing, Wiseman says, time is money and paint pads don’t have enough capacity. In addition, he adds, because paint pads are thicker and tackier (stickier), high-solids coatings will pull the flocked fibers from the paint pad and ruin the finish.
Painters who may have used brushes and rollers extensively in the past may turn to spray application of low-VOC paints in response to the quicker setup time of these coatings. While this is an effective solution, there are still some cautions.
It’s a good idea to start with the lowest pressure possible and increase it slowly until any “fingering” disappears.
Will you be backrolling? If so, says Armstrong, “backroll immediately to ensure proper flow and color development.” Again, use a humidifier to help slow down the dry time in the room if the conditions are warm and dry.
Wear and tear of spray equipment is another issue with low-VOC coatings. Greenwell reports, “Low-VOC paints may cause earlier wear of spray tips and pump packings, and may cause more frequent cleanings of ‘in-line’ strainers.”
Overall, the durability of low-VOC paints is very good — according to some, often better than traditional coatings. For that reason alone, the use of additives to extend the wet time of these products can be problematic.
As Armstrong points out, “traditionally additives detract from the overall film properties.”
In addition, using additives may impact or void product warranties.
Greenwell cites other examples of problems using additives: With latex paints, some wet-edge extenders may result in an “after tack” that leads to dirt pickup and less resistance to mildew growth. And wet-edge additives may cause more yellowing of interior oil-based paints.
The most important issue with extenders and additives, however, is the legal one.
While legal additives are available, many wet-edge extenders add VOCs to the paint. And as well as it may work, Schneider observes, “It is illegal to use paint thinner in VOC-compliant oil paints.”
If you decide to use an additive to increase workability, be sure you remain in compliance with your local and federal VOC regulations.