How Shiplap Works
(Note: In the images below, gaps and angles are exaggerated for clarity.)
Dry fit your pieces. Notice that the top edges touch first, making every seam perfect.
As you trowel your glue and begin to lay the PlasDECK, each new strip is pushed gently towards the previous strip. Glue gathers and fills the space between to create a seal. Any excess is pushed up to the surface and cleaned off with denatured alcohol.