Flexner on Finishing: Slow Drying


Why stains and finishes sometimes dry slowly.
By Bob Flexner
Pages: 82-83

From the April 2008 issue #168
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A friend called with a problem. He had applied an ebony oil stain to oak and after the stain had dried for two days, the polyurethane he then brushed picked up some of the color and smeared it around the surface.

Was there a problem with the stain, or did he do something wrong?

Well, I could think of several possible problems with the stain. First, a very dark stain requires more pigment. So maybe the manufacturer just hadn’t added enough binder (oil or varnish) to encase all the pigment well. Second, some manufacturers are replacing solvent with slow-drying oils to comply with California VOC rules and then selling this product to the entire country to avoid having to make two lines. Oils dry slower.

But my first thought was the weather. Though it had been mild lately, with highs in the 60s and lows in the 40s and 50s, that’s still too cool for normal drying. Most stains and finishes need at least 65° to 70° temperatures for eight hours or more to dry at a normal rate. (Exceptions are water-based stains and finishes, which are affected more by humidity than temperature; and lacquers, which can be made to dry normally in cold weather by adding acetone or fast-evaporating lacquer thinners available from auto-body supply stores.)

So I asked about the shop temperature while the stain was drying. My friend assured me he had heat, but on further questioning he revealed that he turned it off at night.


From the April 2008 issue #168
Buy this issue now