Always, every fiber cement comes with a trade line .like this
The purpose is to detect felt distortion and take the necessary corrective action. Causes of trade line distortions are generally caused by:
1 – Variation of the parallelism of the sheet machine rolls
2 – Different weight of the elementary layer on the felt
3 – Bending of the felt rollers
4 – Variation of the formation pressure on the sheet
5 – various – in the event the felt is too wide or becomes wider because of inadequate tensioning systems and therefore becomes necessary to trim the same, the easiest way is to trim the felt along the machine direction yarn, exactly between the two MD yarns.