Background: Up to 50% of all long-term catheterized individuals experience recurrent episodes of urinary catheter infections and blockages, leading to urine retention, pyelonephritis and septicaemia if the catheter is left in situ. We have previously reported the synergistic activity of weak organic acid (WOA) combinations against nosocomial uropathogens. Aim: To investigate the efficacy of selected WOAs, citric acid and propionic acid, alone and in combination, on prevention of crystalline biofilm formation and catheter blockages. Methods: Static crystallization assays and dynamic in vitro bladder model assays, with scanning electron microscopy, were performed for determination of bacterial viability, urinary pH and time to catheter blockage. Findings: The rate of encrustation around the catheter eyeholes was reduced in the presence of the citric acid/propionic acid combination, extending the time to blockage three-fold. Conclusion: Synergistic WOA combinations identified herein represent promising alternatives to antibiotics to combat the global healthcare burden of catheter-associated urinary tract infections and related blockages.