The valorization of waste fishing trawl (WFT) and waste fishing rope (WFR) fibers in cementitious materials (CMs) has gained attention in recent years; however, the lack of information on the cutting and cleaning techniques for these fibers hinders their widespread commercial utilization. Existing research primarily relies on manual cutting, which proves to be impractical for large-scale production due to its time-consuming nature and lack of industrial feasibility. This research is a component of the VALNET project and introduces an innovative technique that utilizes the cutting mill to convert WFT and WFR into fibers to effectively overcome the constraints of earlier methodologies. By employing a rotor with blades, this apparatus enables efficient and precise cutting of WFT and WFR, eliminating the need for labor-intensive manual cutting. The sustainable cleaning of WFT and WFR was carried out utilizing rain and wind by placing them outside for a certain period of time. The advancements presented in this study provide a pathway for an efficient and scalable valorization of WFT and WFR fibers in CM. The study focused on analyzing the impact of varying fiber sizes and percentages on the mechanical properties of CM. Different sizes obtained from the cutting machine and different fiber percentages were examined to gain a better understanding of their influence. The fibers obtained by the utilization of a 20 mm sieve yield optimal outcomes, while the incorporation of fibers at a volume fraction of 0.5% yields the most favorable results. Furthermore, the study presents evidence of a noticeable rise in porosity resulting from the incorporation of WFT and WFR fibers, regardless of their size and proportion. Porosity slightly increases as the fiber length increases, but the rise in fiber proportion leads to a significantly greater increase in porosity.