Square butt welds are used on light-gauge sheets through 3/32 inch. No preparation of the edges is
required other than cleaning. A root gap of 1/64 of an inch is used to allow for full penetration of the weld.
In welding two plastic sheets by the butt-weld method, the sheets must be held together on a flat surface
by some type of clamping device or by being weighted down. Two passes are recommended in making a
square butt weld – the top pass and a pass on the under side.
The square butt weld is an acceptable weld for all ordinary loads. It is simple to make and is used where
cost is the principal consideration. In making a square butt weld, care should be taken to be sure there is
complete fusion of the edges of the sheets.