（b）the substitution of proper and suitable materials； and
（c）the removal and proper reexecution， notwithstanding any previous test thereof or interim payment therefor， of any work which in respect of materials or workmanship is not， in the opinion of the employer， in accordance， with the contract.
in case of default on the part of the contractor in carrying out such order， the employer shall be entitled to employ and pay other persons to carry out the same and all expenses consequent thereon or incidental thereto shall be recoverable from the contractor by the employer， or may be deducted by the employer from any monies due or which may become due to the contractor.21 suspension of work
the contractor shall， on the written order of the employer， suspend the progress of the work or any part thereof for such time of times and in such manner as the employer may consider necessary and shall during such suspension properly protect and secure the work， so far as is necessary in the opinion of the employer. the extra cost incurred by the contractor in giving effect to the employer''s instructions under this shall be borne and paid by the employer unless such suspension is；
（a）otherwise provided for in the contract； or
（b）necessary by reason of some default on the part of the contractor； or
（c）necessary by reason of some default on the part of the contractor； or
（d）necessary for the proper execution of the works or for the safety of the works or any part thereof insofar as such necessity does not arise from any act or default by the engineer or the employer or from any of the expected risks defined in 8（2） hereof.
provided that the contractor shall not be entitled to recover any such extra cost unless he gives written notice of his intention to claim to the employer within twenty - eight days of the employer''s order. the employer shall settle and determine such extra payment and/or extension of time under 23 hereof to be made to the contractor in respect of such claim as shall， in the opinion of the employer， be fair and reasonable.
if the progress of the works or any part thereof is suspended on the written order of the emloyer and if permission to resume work is not given by the employer within a period of ninety days from the date of suspensing them， unless such suspension is within paragraph （a）， （b）， （c） or （d） of sub（1） of this clause， the contractor may serve a written notice on the employer requiring permission within twenty eight days from the receipt thereof to proceed with the works， or that part thereof in regard to which progress is suspended and， if such permission is not granted within that time ，the contractor by further written notice so served may， but is not bound to， elect or treat the suspension where it affects only part of the works as an omission of such part under 28 hereof， or， where it affects the whole works， as an abandonment of the contract by the employer.22 commencement time and time for completion