After reading your explanation, it seems I have received the wrong advice. I have spralling concrete on my bathroom ceiling and I was told to use putty. Another shop recommended using Davco k11 rapid plug. I have a 1kg white cement at hand. What should I use? I have already applied anti rust coating on the exposed bars.

Watching this video makes me understand why the previous repair in 2011 by the contractor failed so miserably. I didn't do my homework then and trusted him. What is the yellow tube thing that was used to seal cracks?
I was told to use sealer paint and Jotun Majestic Sense to cover hairline cracks on the wall.And if the hairline crack is too wide, use putty first. Now I know I have to stand 3 feet away before I call it a hairline crack!

The actual label on the Davco tin doesn't have this description "non shrink grout cement".
....will try to upload a low resolution image tomorrow....I have just found ANOTHER two problem areas:
1) one tiny section of spralling concrete in one bedroom
2) a section of the wall in the sitting room is partially plastered because it was hidden by two cabinets.

https://pictr.com/images/2022/12/27/EUZCvq.md.jpg
This tiny one in the bedroom, I can patch it myself? Putty, white cement or Davco?

Sorry, I am a novice here. You mean scrap off the loose portion and touch the ceiling to see if it is damp after rain (it's raining everyday now) before doing any mending?

https://pictr.com/images/2022/12/28/EUNFyQ.md.jpg

This one can DIY with white cement or putty right? Sitting room wall partially plastered. The unplastered wall held remnants of the old wallpaper. I have washed out the glue with hot water and left it to dry for 2days.

Unless the whole house is under renovation and the workman is always there, all repair work on minor ceiling spralling are completed in one visit. There is no luxury of time for the coating on the rebar to dry or the concrete to set. The contractor will just paint over and move to the next job. This is what I have heard from friends who hire contractor to fix their bathroom ceiling.

You are right. That Davco is 7X the price of white cement and putty. My first attempt to prepare the mix was too slow and the whole mixture turned into a rock before i could apply on the ceiling. Yes, it sets in five minutes. There was no time for proper skimming. I am using Davco now for the bathroom ceiling that has an exposed rebar.

The other cracked ceiling in the bedroom was thankfully just the plastered celing coming off. It wasn't damp. I patched it with putty.....will spread another layer of putty tomorrow before painting over with Vinelex and antimould paint the next day.

Many thanks to diffyhelman2, ceo684 and jojolicia for your advice and reassurance. I got the job done. It was the most difficult part of the painting job.
My apology for a late greeting......Happy New Year, everyone!