Step 1: Verify on the plans of the strata that the balcony is clearly marked as “common property” ie with thick black lines;
Step 2: If you find it is “common property”, then
(a) List all the problems you see with the concrete (render falling apart, paint peeling etc);
(b) Take as many photos as you can;
(c) Write a history of when you first saw the problem(s) and what you did about them;
(d) Record what if anything the OC did when you approached them on the matter
Step 3: Call NSW Fair Trading on 13 32 20
(a) Tell them of the problem(s) and what you have done to address them;
(b) Ask what sections of the Strata Act you can rely on to compel the OC to do its job;
(c) Apply for Strata Mediation (a free service offered by NSW Fair Trading) between you and the OC where a Mediator attempts to arrive at an agreement between the parties. It is voluntary for the OC to attend and any agreement is not binding but Mediation is needed to have been undertaken (successful or not) before you can apply to NCAT (the Tribunal). Mediation can be applied for online and takes under 10 mins to do.
Best of luck.