I have an old 1960's tongue and groove floor that, after some renovations (removing an internal half-height wall), will be joining (butt end-to-end) some new tongue and groove (85mm x 22mm matai)
I had initially hoped to match the old/new board widths exactly and feather in some of the new pieces in to reduce the visual impact of the join, but this is proving to be difficult as although the boards are the same width, the original installers in the 1960's were very inconsistent with their cramping and there are (sometimes quite large) inconsistent gaps moving the ends of the boards out of alignment fairly quickly.
I thinking about routing out a 30m or 40mm wide channel about 6mm deep cross-wise along the join (ie, evenly across the ends of the old/new lengths) and dropping in a piece of contrasting wood to accentuate the join rather than hide it.
This obviously raises concerns about expansion.
Is this likely to be a problem?
(To be clear, I was going to use new matai for the cross piece insert and I'm not at all concerned about the difference in wood color between the new and old matai - after sanding/finishing and a decade of aging I imagine they will look fairly similar. I'm just not a huge fan of the straight-line room-wide butt join running the full width of the room - functionally it's fine, but looks a bit a naff. By putting the cross piece in I'm thinking about making it look more like a feature/ slightly more intentional rather than the constraint that it is)