SERVICE TAX AND VAT

Sir,

       If a contractor doing electrical and repair works and use some consumables  for it, then he has to pay service tax on total contract amount incl. labour and VAT on consumables. Is it correct? If no, then what is the correct method. And, if  the contractor has to pay VAT on such consumables , what will be the rate of tax if the consumables include items of different tax rates which cannot be identified.