With the ever-more strict regulation of wood finishes containing VOCs (volatile organic compounds) along with a general increase in consciousness of health and environmental issues, more and more woodworkers are doing something they never thought they’d do: making the switch to waterborne wood finishes. In the process, many experience a fair amount of "internal resistance". Waterborne finishes are certainly a more environmentally friendly option than oil-based finishes, but how well do they work? In case you're on the fence about waterborne finishes or just wondering how they work, here’s a little information on the chemistry involved, what you can expect from the best waterborne finishes, and a couple of our top picks:
Calling a waterborne finish “water-based” is as common as it is misleading. Waterborne wood finishes are actually solvent-based finishes that just happen to use water as a convenient, logical and environmentally neutral vehicle. If you inspect a blob of wet waterborne finish under a microscope, what you’ll see are minute spheres of resin (most commonly acrylic and polyurethane) suspended in a mixture of water and a slow evaporating solvent, such as glycol ether. When you spread a waterborne finish out in the open air, the water begins to evaporate. The solvent, which evaporates slower, softens the protective coating on the tiny resin “latexes” and causes them to coalesce into one continuous film. Only waterborne finishes behave this way chemically, and logically enough, they're the only ones referred to as "coalescing finishes".
If waterborne finishes were truly “water-based” they’d wash off your project with a wet rag, and wouldn’t be much good for anything. But, in theory at least, when a coalescing finish has cured, it is impervious to water. That doesn’t hold true for solvents or heat, however. Heat and solvents can loosen the bond between the resin droplets and damage the finish or cause it to become sticky. In tests, not all waterborne finishes stand up well to solvents and heat. If you need a finish that will stand up to everyday household solvents like those found in perfume or a bottle of beer, and won’t get ruined if you set a cup of very hot coffee on it, you'd be wise to get some information on how the finish you're considering faired in solvent and heat resistance tests.
How a finish will stand up to use isn’t the only consideration, of course. The finish should be reasonably easy to apply, and most importantly should look good when it dries. There is a wide range in performance and ease of application among currently available products. Unfortunately, the failings of a few have generated a couple of common misconceptions that crop up frequently when it comes to the application and appearance of waterborne finishes. The first myth says, “You can’t spray waterbornes”. The truth is, many waterborne finishes spray exceptionally well. In fact, certain water borne finishes have to be sprayed on for acceptable results.
The second misconception holds that waterborne finishes all have a hazy, bluish appearance, and therefore aren’t any good over darker colored woods or stains. Here again, it really depends on the finish. While none come in the can with the rich amber color you're used to getting from oil-based varnishes, they do vary in dried appearance, with some coming out almost perfectly clear. Generally speaking, the best appearance a waterborne finish can provide is none at all - that is, it should be perfectly clear. If you find that you miss the amber effect, most waterborne finishes can be tinted to the desired color.
How do you know which one to get? The can isn't always the most reliable source of information. Fortunately, there's been enough interest warterbornes in recent year to generate ample debate on the merits of various brands. In the mix you'll find a couple very good independent tests. Based on them, and on what we hear back from wood finishers, here are a couple of top choices:
If you aren’t set up with spray equipment, or prefer to brush on the finish, then General Finishes EF Polyacrylic Blend Top Coat is a pretty safe bet. In the November, 1995 issue of Fine Woodworking Magazine, author and finishing expert Chris Minick tested fifteen waterborne finishes and named EF Polyacrylic the “best brush-on” , adding that this polyurethane and acrylic blend “applies easily, has excellent leveling properties, good vertical cling and looks great – a pleasant surprise in a brush-on finish.” The General Finishes EF Polyacrylic also faired well in stain, solvent resistance, heat and adhesion tests, and as a bonus, sands easy. Here's a customer review of EF Polyacrylic that seconds the "looks great" opinion.
If you really want to finish in style, and want a clear finish that both brushes and sprays exceptionally well, you won’t do better than General Finishes High Performance Polyurethane Top Coat. When Chris Minick came back with his encore waterborne finish test in the November, 2006 issue of Fine Woodworking, he named GF High Performance the “best overall” waterborne finish: “This finish was a dream to work with: it brushed and sprayed easily, it dried flat, it had great protection…” These observations have certainly been borne out in what we hear back about the product, including comments in customer reviews like the one left by Steve in Louisburg, who called it, “the best water based top coat I've ever used.”
We’re not knocking traditional solvent based clear finishes – they’ve been used with great success by woodworkers everywhere for a long, long time. The point is that now you have a health conscious, environmentally friendly alternative that really works. Keep in mind though, that “results may vary” from brand to brand, and it pays to shop around.