Wood Finishing: Clear Wood Finishes for Interiors
Manufacturers are developing both waterborne and modified, oil-based clear wood finishes that meet new low-VOC regulations. The waterborne finishes don't yellow with age, dry quickly and are low-odor. Oil-modified finishes require fewer coats and won't raise the grain on wood.
by Amy Johnson
from modest homes to upscale offices. The art of finishing wood is timeless, but the science is moving ahead at a record pace. Today, one of the biggest issues driving changing technology is the requirement to reduce volatile organic compounds (VOCs).
There are a couple approaches to lowering VOCs, according to Richard Braako, who started his career in product development for United Gilsonite Laboratories (UGL) and now serves as environment, health and safety manager. “One is to modify solvent-based materials by replacing solvents with products not listed as VOCs. Increasing solids by adding alkyds also decreases the proportion of VOCs in a formulation. The second is the development of waterborne coatings.”
While both approaches are in use today, there is continued pressure on manufacturers — typified by stricter local VOC controls in parts of California, New York and Kentucky — to develop high-performance waterborne finishes. Steve Revnew, director of architectural marketing, residential segments, for Sherwin-Williams explains, “This focus on providing painting contractors with waterborne products that not only meet aesthetic and performance needs — but, more importantly, that are also attuned to environmental considerations — continues to signal change in the industry that can only be called ‘revolutionary.’”
According to Kelly-Moore corporate product manager Rod O’Neal, the company achieved compliance with VOC standards by switching to acetone, a solvent exempted from regulation. Kelly-Moore also sells pre-catalyzed lacquer and conversion varnish that are solvent-based but meet VOC requirements. O’Neal says the oil-based formulations are more forgiving than waterbornes. “When you add multiple coats of oil-based materials, the coat underneath remelts, hiding errors. Waterborne materials are less forgiving. Each layer is distinct so flaws are carried through.”
Penofin Performance Coatings achieves lower VOCs by basing its products on a low-solid formula using oil from sustainable Brazilian rosewood seeds, which penetrates more deeply than traditional tung oil and offers better UV protection. According to Joan Griswold, executive vice president of sales and marketing, this product is stain and sealer in one; no top coat is required. Griswold does not believe VOC reduction means the end of beautiful wood finishes. “The industry needs to continue developing products that both perform well in terms of durability, longevity and beauty and meet clean air standards. I think it can be done.”
Dean Camenares, principal at East End Woodstrippers in Holbrook, N. Y., cautions that an acrylic resin can dry to a “whitish” look, rather than clear, if it is built up too heavily. “Acrylic doesn’t have the same warm look you expect from traditional varnish,” he says. “It looks more sterile” — a look that is not really compatible with his company’s mission of preserving irreplaceable original architectural woodwork from old-growth trees found in historic buildings.
The performance and applicability of waterborne coatings is improving all the time. “The most important thing to bear in mind is that waterborne coatings should be your first choice (because of) the overwhelming benefits new waterborne technologies bring to painting contractors,” Revnew says. Sherwin-Williams is developing these new products and technologies to supply user-friendly products that offer improved productivity and better end-user satisfaction as well as regulatory compliance, he says.
One obvious advantage of waterborne materials is they do not yellow with age. Revnew calls the finish “ultra clear.” Contractor Nigel Costolloe, president of Catchlight Inc. in Brookline, Mass., says, “Yellowing is not a concern with waterborne technology; gloss retention is excellent.” Braako cites the same advantage. “Generally speaking, water-based finishes are less likely to yellow. There is nothing in our product that is prone to yellow.” He does caution that an underlying stain can still yellow under certain conditions that have nothing to do with the coating.
Camenares believes the waterborne finish approximates the look of traditional varnish more closely than oil-modified finishes. It also dries more quickly and emits less odor. Braako points out that lingering odor is a problem for new “tight” buildings where inside ventilation carries it throughout the building but limited access to fresh outside air prevents the odor from dissipating.
Waterborne finishes are applied by the same methods — cloth, brush or spray — as oil-based materials, but there are slight differences. Camenares doesn’t believe waterbornes spray as effectively, so he usually brushes them on. He also points out the need for more coats than with traditional materials. Braako explains, “Water coatings are lower in solids so you don’t get the same film build as with oil-based. You may need five or six coats to reach the same gloss you can get with three or four coats of oil-based varnish.” He also warns that a common error is spreading waterborne materials too far, as they have a tendency to spread more readily than oil-based materials. He recommends careful compliance with the spread rate calculated by the manufacturer to achieve the correct film thickness.
There is general agreement that most waterborne materials dry to a softer finish than oil-based ones. Braako confirms that water-based coatings never get as hard as oil-based urethanes, so they may not be as durable. For this reason he recommends using oil-based systems on floors. In contrast, Revnew describes the Sherwin-Williams Wood Classics product as tough and durable.
Kelly-Moore’s O’Neal admits there are still some technological challenges to the development of widely accepted waterborne finishes. “The problem is grain-raise on new wood. The water penetrates the wood and swells the grain. We are working to keep that to a minimum and the technology has come a long way. I definitely think the trend is to waterborne.”
Perhaps the biggest hurdle is contractor resistance — new habits are difficult to form. Sherwin-Williams’ Revnew frankly says, “The only case where I see an oil-based product being preferred is when a contractor believes that the product is better. Typically, with proper education contractors will learn the advantages of waterborne products.”
Stronger local VOC regulations, workers’ compensation issues and solvent disposal restrictions are all factors that encourage contractors to consider a switch to waterborne lacquers and finishes. But as the technology develops, the best reasons may be better performance and easier application.