Just FWIW, and in a pinch ... and perhaps too old fashioned/cheesy for most
these days, but I've occasionally used a method learned from an old cabinet
maker in England many years ago:

"string" or "twine"

... the baling variety works fine.

Judging from the work of his ancestors (pieces that were still doing what
they were made to do), it appears to have worked for at least a couple of
hundred years.


I've always understood this as a fairly common practice. Also, wooden
boats are chinched with jute rope and old plank floors have rope
chinching, after they have dried and shrank. Agreed, rope as an
expansion material, this way, is certainly not new. Rope can be
stained, as well, to match nearly any color needed. Whether rope or
baling twine, dipping in wax, before applying, is common, also, though
I am not sure about this on/in panel applications.... certainly can't
hurt. In a pinch, waxed rope can seal a boat's shaft from water
leakage.

In a home, near here, someone tried to fill gaps in a plank floor with
tile grout. What a mess. I couldn't believe that.

Sonny