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 In Flexner On Finishing, Flexner on Finishing Blog, Shop Blog, Techniques, Wood Finishing

A hard maple board that was dried properly, so no sugar bleeding.

I get newsletters from a website called www.woodworkingnetwork.com. You should be able to sign up by going to this website. The website targets factories and larger shops, but the information can be used by anyone.

One of the regulars on the website is Gene Wengert, who is better known as The Wood Doctor. Gene is a wood technologist and used to work in Madison, WI in some capacity with the Forest Products Lab before going out on his own, writing about wood. I found an archive of Gene’s work at this website.

In one of his latest contributions to the Woodworking Network, Gene tells the story of a shop that had recently switched to water-based finish and was having a problem on hard maple, but just from one supplier of the wood. The problem was described as sugars from the maple working their way through the finish and creating a white frost on the surface. Why was this happening and why from just one supplier and not the others?

Gene explained that expensive chemical tests would have to be done to definitively find the cause, but he was willing to speculate.

He confirmed that hard maple did indeed contain sugars and that these sugars were soluble in water. Normal drying schedules for hard maple called for using temperatures of 150 degrees Fahrenheit or hotter, and these temperatures changed the chemistry of the sugars so they wouldn’t bleed out when the wood was dry.

So Gene speculated that the supplier was drying the wood using lower temperatures, with the result that water-based finishes dissolved the sugars and caused them to bleed to the surface. Gene suggested the shop get in touch with the supplier and see if this was the case. In the meantime, of course, the logical solution was to just stay with the other suppliers.

I tell this story because of how unusual it is and because it gives me the opportunity to introduce you to the Woodworking Network and to The Wood Doctor. I find both very interesting to read.

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Showing 2 comments
  • MikeyD

    Hmm…. It seems an interesting problem. I’ve looked into drying procedures, considered building my own kiln. One of the problems frequently mentioned is the issue of “case hardening” some hardwoods, with hard maple in thicker dimensions mentioned as a typical example. Drying at too high of a temperature means the outside of the lumber dries relatively quickly and first, creating a barrier for moisture from the center of the wood. It leads to an outside layer much harder than the rest, creating workability problems. Sounds like temperature control is critical and trying to do this casually is not a good idea.

  • Neitsdelf

    So, don’t use water-based finishes on air-dried maple, or lay down a coat of shellac first?

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