The most common mistake is placing the tape on a frame that is too narrow. The tape supplied is 15 mm wide. Frames must provide a flat surface at least 15mm wide (30mm for large windows) in order to provide sufficient area for adhesion when the membrane is under tension after shrinking with the hair-dryer.
Some enthusiasts neglected to adequately clean window frames which had acquired a greasy surface over the years. Others applied the tape directly to unpainted wooden frames, not realizing the timber had been treated with an oil or wax protective coating.
Frames painted long ago should be cleaned with a solvent such as methylated spirits. Oiled or waxed frames, and rough-sawn timber surfaces, must be sanded down to reveal fresh, smooth timber in a ‘Dressed And Ready’ condition before applying the double-sided tape.
See: Window frames treated with oil, wax, or in poor condition