Is it permissible to withhold the remaining dues of a worker (plasterer and painter) due to his poor workmanship and delayed completion, especially when there are defects that require rectification at the original employer's expense?

You have the right to deduct from the worker's wage an amount equivalent to compensation for defects in his work. It is permissible to deduct the wage of a worker who was late in completing the work or did not complete it as agreed. The deduction should be commensurate with the compensation for defects and the damage resulting from the delay. Experts should be consulted in assessing these matters.