Finish Test Follow-up: A Surprise Ending
Three days after performing the finish experiment I wrote about in last week’s post, I was cleaning up the mudroom and had to move the samples. When I picked up the one finished with Osmo Polyx Oil, I was astonished to find that the stains from red wine and hot sauce had disappeared completely. I looked at the Cabot water-based poly and Minwax Helmsman spar varnish samples, which had also been stained by the hot sauce. Not a trace remained. After pinching myself to make sure I wasn’t dreaming, I concluded that more research was called for.
I called the technical department at Minwax to ask about the spar varnish. The staff person I spoke with said that as a finish intended for indoor and outdoor use, their spar varnish is formulated to expand and contract with changes in the wood’s moisture level; this keeps the finish from cracking. Based on the process I described, he suggested that the finish film expanded (at the molecular level) and allowed the hot sauce to penetrate at least partially into it, though not into the wood. When the hot sauce was wiped off and the residual moisture (vinegar and water) evaporated, poof! there went the stain. Note: He reminded me that the manufacturer recommends a 30-day curing period.
I called the technical department at Cabot next to inquire about the behavior of the water-based poly. “You may not believe this,” said the person on the other line. “You just asked me the same question about Minwax spar varnish.” Both Minwax and Cabot are now owned by Sherwin Williams. He suggested the same explanation for the stain’s disappearance from the water-based poly sample, adding that the Cabot product has a higher solids content than some water-based finishes.
For insight into the Osmo sample, I called my supplier, World Class Supply (worldclasssupply.com), and explained what I’d observed to the owner, Reid Rowlands. He asked about the wood species, grit to which I’d sanded, and application process. He pointed out that with a close-grained hardwood species such as hard maple, which would inherently be less absorbent than many others, sanding to 220 grit was excessive; the finish would penetrate better (as Osmo is intended to do) if the substrate were sanded to a less-fine grit. One likely result of sanding hard maple to 220: You increase the possibility of over applying and having wax build up. (Full disclosure: I saw no evidence of wax build up. The finish was satin smooth to the touch and as matte as I have ever seen with Osmo Polyx Oil.) He also said the third coat I’d applied was not necessary and that I may have wiped off as much as I put down with the third coat. “The wood will drink as much of the Osmo product as it wants,” he wrote, and “when it’s done, it leaves the excess on top that needs to be buffed off or there will be built up wax.” What was clear to us both was that while the finish had apparently absorbed the pigment from the red wine and hot sauce, the stain had not reached the wood. In other words, the finish had protected the substrate. And in the three days since the experiment, whatever moisture had penetrated the Osmo and left its mark had evaporated, taking the apparent stains along with it.
The moral of this story:
Each of these finishes performed well. I am tempted to add that the three mentioned in this post performed a miracle – and that would not be hyperbole, considering that the word basically means a marvelous event. Each has its particular method(s) of application, which may be suitable for one person’s shop situation and not for his or her neighbor’s. Each also promises a higher or lower sheen and more or less ambering. Based on my test, the suitability of the application and drying process, along with your preferred degree of sheen and ambering, appear to be the salient differences between these products, at least for interior use.
Note: Follow the manufacturer’s recommendations for applying finishes and allowing them to cure before you subject them to abuse.