Finish Test: Water vs. OilComments (0)
This article is from Issue 40 of Woodcraft Magazine.
Is it time to close the lid on oil-based poly?
By Craig Bentzley
I opened my first can of water-based finish over 20 years ago. Lured by the promise of easy cleanup, low odor, fast drying time, and nonflammability, it seemed to be the perfect clear-coat solution. Unfortunately, these first-generation finishes were difficult to apply, didn’t hold up well, and just looked bad. Like many woodworkers, I closed the lid on these newcomers and stuck with solvent-based varnishes and lacquers.
Since then, stricter regulations limiting the amount of volatile organic compounds (VOCs) have driven manufacturers to further develop better water-based formulas. Ready to give water-based finishes a second chance, I compared five commonly available products against two popular alkyd varnishes. Surprisingly, the results were convincing enough to make me reconsider my old go-to finishes.
Ease of application
All of the finishes sprayed nicely. Based on my results, it’s hard to imagine a situation where a small shop woodworker would want to spray anything else. I was pleasantly surprised to discover that several of the finishes brushed out quite well (see chart, page 35)—provided that you use the right brush.
As shown in Photo A, above, garden-variety polyester brushes introduce bubbles and brush marks into the finish. Taklon brushes, available from art supply houses, or Wooster’s “Alpha” brushes, available at paint stores, have soft bristles with straight or tapered ends that allow the finish to flow more smoothly.
In terms of drying times, all of the waterbornes left the alkyds in the dust. Faster drying means that a project can be completed in a fraction of the time required by oil-based counterparts. For example, a small side table can be finished with four coats in one day, versus a day and a half using traditional products. In all cases, the waterborne finish samples were ready for scuff-sanding well before the recommended (on average, two-hour) drying time. The samples sanded easily, producing fine dust without clogging the paper.
It’s worth noting that grain-raising was a nonissue. I did not need to dampen the stock prior to applying the first coat.
What’s In The Can?
Getting manufacturers to divulge their product ingredients is tantamount to obtaining missile launch codes. At the risk of over-simplification, most water-based finishes fall into two categories: modified resins that are suspended in water, and hybrids made of water-absorbing resins.
You don’t need a chemistry degree to understand that you get what you pay for. I had to apply more coats of the least-expensive finishes to match the look achieved with the pricier product, costing time and negating savings. Surprisingly, even with the additional coats, the less expensive finishes weren’t as stain resistant as the pricier competition.
First-generation finishes were criticized for having a bluish cast. These days, such is not the case. With one exception, the finishes dried crystal-clear, much like nitrocellulose lacquer. In contrast, General Finishes Enduro-Var had a slight amber tone, similar to alkyd finishes.
If you’re looking to enrich the color of woods like cherry and walnut, you’ll need to add another step to your finishing process, such as staining the wood or tinting the finish. (I prefer staining the wood with aniline dyes, because they offer more control and dry quickly.)
Although all the finishes I tested were labeled “semi-gloss,” the sheen varied from product to product. The Minwax Polycrylic was shinier than the other products, while the General Finishes Polyacrylic was the flattest. Minwax’s finish was also the least viscous and required more coats to achieve the same build as the other finishes.
If you wipe up spills quickly enough, even a waxed surface can qualify as “stain-resistant.” The real problems come from the messes that you fail to clean up. To that end, I prepared the sample boards, staining half with an oil-based stain, allowing 48 hours to dry, and then brushed on four coats of finish. After giving the finish samples a week to cure, I applied six real-world staining agents: red candle wax, red wine, mustard, Fantastik spray cleaner, nail polish remover, and rusty steel wool soaked in vinegar and let them dry overnight (Photo B).
As expected, the most dramatic damage took place on the lower priced finishes, with the rusty steel wool/vinegar having the biggest impact on all samples. For complete results, see the chart at right.
To test heat resistance, I filled a ceramic cup with boiling water and placed it on each sample, allowing it to cool (Photo C). Surprisingly, none of the samples had objectionable damage, and all fared comparably to their alkyd counterparts.
To test for finish adhesion, I cut a grid of 10 squares to the inch into both the stained and unstained side of each sample with a knife (Photo D). A strip of clear packing tape was burnished over the grids and allowed to sit overnight before removal. All of the finishes performed well on the unstained section. Surprisingly, both alkyd finishes and the Enduro-Var had adhesion problems on the oil-stained surfaces.
Compared to the early generation of waterbornes, all of these finishes are winners, but General Finishes Enduro-Var impressed me the most. The Enduro-Var was easy to apply, provided a warmth that most resembled oil-based urethanes, and offered the most protection. If I wanted to cut costs, or needed to pick up a can of finish at the hardware store, I wouldn’t hesitate to use Varathane’s polyurethane. For good protection without the amber color, I’d use General Finishes High Performance.
I'm not ready to surrender shellac and may continue to use alkyd finishes for some projects, but after this test I’m making room for waterbornes in my workshop. If solvent-based lacquers and polyurethanes were to disappear from store shelves, I think woodworkers would do just fine without them.
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