Reply by jmos

One of the concerns I’ve always had about dados is that there is no long grain to long grain glue surface, and glued end grain is not that strong. I’m not sure you really even get much strength from the area you accidentally finished. But, having said that, I wouldn’t want to try it without that surface, especially in a large piece that will hold weight.

I think masking and sanding the inserted area is the way to go.

Another possibility, not as good but absolutely solid, would be to glue up what you have, and use some screws from the outside (start by drilling small holes centered in the dado’s from the dado out to make sure they are perfectly centered, then drill through and counter bore from the outside). Plug the holes and finish the plugs. It will keep the dados together, but hiding the plugs can be tricky.

Good luck.

edit – another thought in lieu of sanding, try a scraper to take off the finish, probably easier to control, faster, and less dust.

-- John