Flipping the tongue with hardwood flooring is a standard technique. Doesn’t involve cutting grooves and doesn’t involve butt joints. Jussayin’.Butt joints are used all the time, and with no problem. Here are a few examples of how a transition is normally accomplished, and another example of laying a boarder. In none of these is a spline used. It isn't used for two reasons. The first being that it just isn't needed. The second is that more damage could be done by attempting to put a groove in for a spline.
Bamboo Wood Flooring/Part 13/How to install No Threshold Perpendicular Flooring - YouTube
Installing Hardwood Floor Borders - YouTube
How to Add On to a Wood Floor Design with Border - YouTube
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