Moisture Movement of Mixed Wood Species

Mixing species in a single furniture piece is no problem in most situations, but could create an issue if there are drastic changes in ambient humidity. March 30, 2008

Are there woods that shouldn't be joined together due to movement differences or any other factors? Let's say I was to build a project using an exposed sliding dovetail tenon joint with two different species. Is there more likely to be a joint failure if you used one wood that has very little movement and another that has a tendency to move more dramatically?

Forum Responses
From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
As you probably know, there will not be any substantial movement if there is the normal yearly RH cycling inside a dwelling. So, the small difference in shrinkage between commonly used woods will not be an overwhelming factor. What is typically the trouble area is when there is a major change in MC from the shop (or dry kiln MC) to the dwelling. Oftentimes, the change in MC is very large, although it does not have to be if the kiln and shop are properly controlled. So, my advice is to watch your incoming MC of all species used so that it is very close to the MC in use and you can easily mix woods.

For softwoods, we find that they machine better above 9% MC; for hardwoods, closer to 6.5% MC is preferred. Mixing hardwoods and softwoods can be an issue as the MCs are not matched close enough.