Tibouchina Emergency Surgery

Due to losing my conservatory to an extension this winter I was forced to leave my Tibouchina urvilleana out in the cold.  Inevitably it withered and died.  I bought it back inside when I could (more in hope than expectation) and pruned it down to a short framework.  Sap poured out of the pruning wounds and after a while they were covered in a white mould like substance.  Yesterday I took it out to perform a mercy killing only to see some new buds further down the plant!  I decided to prune again to remove the 'mouldy' branches.  Once again the sap is pouring - how can I prevent the mould reforming and actually will it be harmful to the plant if I leave it?