7. If any work required by a notice served under section 6 be not executed to the satisfaction of the Board within the period fixed by the notice, or within such further period (if any) as may be allowed by the Board, orIf any work executed in pursuance of any such notice be not maintained in repair to the satisfaction of the Board, orif any operations required by any such notice be not carried on to the satisfaction of the Board, the Board, after serving a warning notice on the defaulters, shall prepare an estimate of the cost of the work which ought, in their opinion, to be carried out, and may entertain any establishment necessary for the preparation of such estimate, and may also cause such work to be executed.