High spot or remnants.. use a block of wood and 80 grit rough sandpaper remove excess material dulu.
Wipe down w damp rag remove loose dust.
The roughage is good for putty to adhere to.

Putty has expiry date so chk when buying.
If u open up the putty tub let it breathe 5 min like wine then it stick better and more pliable when compressed with metal scraper.

White cement need to cure longer. Otherwise when u paint over uncured part the gassing off makes pimples on the paint.

looks to be the same thickness as the pink part, just unpainted. paint it pink instead of plastering.

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.

Good to hear that, normally i use davco type products to seal gaps in drains and joints where water is flowing, thus the need for a very quick setting mortar. The other use for that type of cement is to “hold” rebar or some other pieces of item i need to place on concrete before applying the main concrete. It sets so fast that you can use it like an extra pair of hands.

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!

depends on what u use for. small internal wall cracks or holes use putty. bigger cracks use cement