Q. I am making replacement wood columns that require, due to historical authenticity, 10 staves that are joined with a spline. The column shape is called a regular decagon...I took geometry and actually learned something that proved to be somewhat useful. We are in serious discussions about the correct adhesive to use to be historically correct. It looks like there was no adhesive used in the original columns, but maybe it was hide glue and it has disappeared over the years. What do you think about adhesives?
A. If the columns are not structural, but just decorative, you can make them with very little, if any, adhesive. Take the spline and put it in an oven for six hours before you use it. This heating will dry it out and cause it to shrink; so the spline will fit fairly well at first, but will fit very tightly when the moisture is returned to its in-use level. If the spline is also long enough, the geometry of the decagon will maintain its integrity.
The only risk is if decay or rot fungi get in and start to weaken the wood itself. Do what you can to limit wetting, as all rot requires high moisture.
Note that the groove for the spline will get smaller as the wood dries...actually, the wood around the groove is shrinking which causes the groove to get smaller. (The groove itself does not have any forces to cause it to shrink or swell.) So, if the staves are a bit high in MC (final in-use MC is 12 percent MC in most situations and locations--fine tune this as needed) and if the spline is real dry at the time of assembly, you will have a tight column without an adhesive.
When making chairs in the old days (1800s), we often would have wetter legs and very dry stretchers, which were connected to the legs with a dowel at the ends. Sometimes we would just put the dowel end into hot sand to dry and shrink the end just before insertion. We often use very dry dowel pins even today, counting on their swelling to get a super tight joint, even with adhesive.
If the columns are structural, then you need to be concerned about the strength in the long term. A structural adhesive would be the only way to go.
Have something to say? Share your thoughts with us in the comments below.