If you go to the link above it will really help you. Butted panels leave a small crack "canyon" between the panels. The single very thin line of tape placed over the penciled line then primered over until the edge of the tape is level then sanded down until you see the tape will leave a crack or canyon and look as thought two panels are placed against each other.
Carl
ORIGINAL: RubenJ
I want butt jointed panels, so I put two strokes of tape along both sides of the lines?