Crazing from Body Sweat - Popular Woodworking Magazine

Crazing from Body Sweat

 In Flexner on Finishing Blog, Woodworking Blogs

Close up of crazing from body sweat on a chair’s crest rail.

All finishes craze ­– that is, develop small cracks – as they age, especially if they are exposed to a lot of sunlight. But there’s another type of crazing, and it can happen much faster. This is crazing caused by body sweat.

You commonly see crazing of this type around cabinet-door pulls and drawer handles, and on chair backs, arms and wooden seats.

This type of crazing is caused by the acids in body sweat slowly breaking down the finish. The finish also softens and becomes dirty as dirt sticks to it. In severe cases the finish separates into small “islands.”

The finishes most prone to this type crazing are lacquer, shellac and water-based finish. Cross-linked finishes such as oil-based varnish and polyurethane, and two-part catalyzed finishes, are much more resistant.

If the crazing is superficial, you may be able to remove it by abrading with steel wool or an abrasive pad and still leave enough finish in good condition underneath to be functional. But usually, when the crazing has become bad enough to get you to do something about it, it’s too late for this. The finish has to be stripped and replaced, which usually means stripping and refinishing the entire door, drawer or chair.

— Bob Flexner


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Showing 7 comments
  • Steven Davis

    So, if we expect heavy handling, we should either “pull a Schwarz” with something like a soap finish that will develop character with handling and use or go to a crosslinking finish and expect to strip and refinish every XX years.

    There is a real argument for “starting with the finish” and going backwards through a build.

    Thank you.

  • bowmandk

    So preventing this sort of thing is all fine and dandy, but I suppose a more interesting question for a preservation expert might be how do you replicate this?

    • Bob Flexner
      Bob Flexner

      This type of crazing (showing small “islands”) can be approximated pretty well with crackle lacquer, for example, from Mohawk Finishes, and maybe from liquid hide glue and latex paint or water-based finish. I’m not so familiar with this process. (Maybe I should do an article in Popular Woodworking.) But I don’t know a way to imitate the type of crazing that occurs from age (light and oxygen). I wish I did.

  • Cal1948

    Crazing on cabinets:
    Sweat and oil are bad enough. Now I am finding family members cook partially under cabinets and steam the finish with coffee makers, electric rice makers and the like. What non paint finishes are able to stand up best to this near daily episode steaming?. Should we give up and go to “paint.”?? Until I read the above discussion on crazing, I was thinking some form of polyurethane or simply go to an oil rubbed finish that can be easily “refreshed”


    • Bob Flexner
      Bob Flexner

      Polyurethane if you’re brushing or a two-part catalyzed finish if you’re spraying would be the most resistant to damage. Your suggestion of an oil finish, often refreshed, is interesting. It might work. But keep in mind that you’re going to stink up the house every time you do the refreshing, and you’re probably going to become lax in time and there will be problems. Oil doesn’t really offer any significant protection to the wood, especially from water or steam, so you’ll have to refresh often. But after many coats (after each deteriorates), sanding smooth between each, you might get a situation you could live with. At least, reduced grain raising.

  • Steven Davis

    What finish options are there that are both resistant to humanity and reversible or repairable?

    Oil-based varnish?

    Or, if reversibility is tricky, what would be most easily repaired from the terrors of humanity?

    And how well does wax protect over a finish from people of regularly refreshed?

    • Bob Flexner
      Bob Flexner

      Great questions. Resistance and repairability are opposites. Resistant film-building finishes are crosslinking finishes: varnishes and two-part finishes. Repairable film-building finishes are evaporative finishes, shellac, lacquer and, somewhat, water-based finishes. All finishes are “repairable” by adding another coat on top. This is what you’re doing with oil finishes, for example, when you want to “refresh” them, even though drying oils crosslink. Adding another coat of oil works well because there’s no build. Adding another coat of film-building finish often doesn’t work so well because of the damage caused to the existing coats.

      Wax adds scratch resistance (slickness) and shine (if the surface is dull), but it adds nothing for protection. That it does so is one of the great myths in woodworking. Moisture goes right through it unless the wax is thick as you find on the ends of some exotic woods to reduce checking. Wax buffed out as a polish adds no protection.

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Bill Rainford jointing a board