Construction Supervisor Carlo Diponio is working alongside specialist concrete repairer Martin Baker and apprentices Aaron Gelder and Nathan Beaman, using a cleaning machine which pumps out steam at high temperatures.
The repair programme will take around 12 weeks to complete - with a full week needed to clean the left side of the Sealion Pool.
Work was originally due for completion nearer to Easter.
Zoo bosses today said it had been finished earlier due to the project being carried out by in-house apprentices rather than an outside organisation.
Firefighters battled the blaze for more than three hours before bringing it under control by 9.16am.