Stir the Finish – Unless it's Gloss - Popular Woodworking Magazine

Stir the Finish – Unless it’s Gloss

 In Flexner on Finishing Blog, Woodworking Blogs
flatting agent

Flatting agent from the bottom of the can.

I have a confession to make. No one knows I did this, at least no one who speaks English, not even my wife. But you are about to know it.

In 1974 my wife (who is Danish) and I moved to Denmark to try to live there. Things were not good in the United States. Nixon had just resigned because of Watergate, and the economy was bad because of the first oil crisis. We had always talked about trying to live in both countries before settling on one. This was a good time in our lives to try Denmark.

For the first year or so, my wife worked. I learned Danish, took care of our two small boys and turned a former small grocery store on the ground floor of one of the typical, block-size, early 20th-century four-or-five story apartment buildings you see all over Northern Europe, into an apartment.

Then it became time for me to get a job. I had a lot of experience with woodworking, so I went to the cabinetmaker’s union to see if anything was available. The economy was bad in Denmark, too, of course (stupid us; we didn’t realize this), so there were no openings. But there were some cabinetmakers who were willing to hire for finishing.

I picked the one closest to our apartment and went for an interview. The foreman asked about my experience spraying. My Danish was OK but not that good, so I hid behind that while I exaggerated and asked that the finisher I was replacing stay over an extra day to show me the system.

I got the job.

Several days later the foreman came into the finish room and asked me about the sheen of the pieces I was spraying with a catalyzed lacquer. The sheen was too glossy. Was I stirring the finish before spraying it? I wasn’t! My predecessor hadn’t mentioned this.

Big lesson. Any finish with flatting agents (to make it satin or flat) has to be stirred, or shaken mechanically, before applying.

I wish I were the only beginning finisher who has made this mistake, but I know I’m not. Be warned. If there’s any solid material on the bottom of the can, stir it in.

— Bob Flexner

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Showing 5 comments
  • John in Calgary

    Conversely, if you don’t mix in the stuff at the bottom properly each time you use the can, remember not to try to stretch the can to finish a project, otherwise you’ll just end up having to remove the final coats that ended up being only flattening agents!


  • DaveS2

    I generally stir all finishes on the assumption something in it has settled or separated. Are there any finishes where this could cause problems?

    • Bob Flexner
      Bob Flexner

      Not that I know of, and I really doubt there are any.

      • EastCoastWoodworker

        What about the old adage that stirring or shaking adds air bubbles into gloss varnishes (honestly, until I read your article just now, I thought this applied to all varnishes)? My method to date has been to gently stir until no solids appear on the stir stick, I also gently scrape the sides of the can.

        • Bob Flexner
          Bob Flexner

          Shaking will add bubbles. You can see them in the can. So it’s better to stir because unless you stir very vigorously, you won’t add bubbles. But…the activity that adds bubbles in your finish is brushing! The bubbles created in the can by shaking or stirring vigorously rarely transfer to the wood. It’s the turbulence created by the brushing that adds these bubbles. I’ve read that you can prevent this by brushing very slowly (so as not to create the turbulence). The instruction was one foot every 8 seconds. Try it! You better allow a lot of extra time. 🙂

          Some brands of varnish (all sheens) bubble less than others, and the bubbles pop out easier in some vanishes than others. Unfortunately, most of the brands have disappeared, leaving Minwax to dominate the market. In my experience, Minwax is among the worst for bubbles, but they do pop out pretty easily. You can usually help the bubbles pop out by brushing over lightly. If you’re still having trouble with bubbles, thin the varnish with 5 or 10 percent mineral spirits (paint thinner). This will give the bubbles more time to pop out on their own.

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