Q.  We have some jatoba pieces and they seem to have a lot of splits developing after we finish the pieces...like a month later when installed in a home.  We checked the MC on the returned pieces and it checked ok.  Any ideas?

A.  Jatoba is a very dense and extremely strong wood species.  The wood does not shrink much...8% green to oven dry maximum.  Small change in humidity and moisture content of kiln dried wood will not create enough stress to initiate new checks or cracks.  Therefore, the cracks you see opening are preexisting cracks that are hard too see until the wood is exposed to dry conditions.  A small amount of shrinkage means that the cracks reopen.

Jatoba is know to develop checks and cracks in drying, especially if it is dried too quickly.  Over-drying under 7.0% MC also means the wood will behave in a brittle manner when machining.  This can accentuate cracking, but such damage can be hard to detect until exposure to a low humidity, such as in the wintertime in a heated home.

Incidentally, when measuring MC, it does little good to check the pieces after defects develop, as the defects mean that the moisture has changed.  So, you will almost always see low MCs after seeing the defects.  The important measurement is the MC before the defects are seen; that is, before the piece dries.

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.


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