So being kind enough, I offer to actually tear down those hollowness becos of safety issues. They had kids at home, if due to your renovation, the plastering drop down, it will either be a large piece or sharp edges. And tot they were kind enough to lend me a ladder, a hammer and a scrapper, I started to tear, check, tear, check(hollow parts)
In the end, the whole kitchen ceiling become like this, where u can see the rockstone and plaster.
I spent 11/2 hr there doing all this. And after that, I offer to do it for the master and common bath. But before doing the rest, I told them, it will be different cost if they want to engage me to scrape off the whole ceiling for the 3 areas, including scrapping off the rockstone, paint sealant and then follow by 2 coats of painting.
Upon hearing the cost, they said its was my own fault... ....for tear down the hollow plaster. Which before I begin to tear down, they was informed already and they agreed to. Initial I only used my hands, they was the one to pass me the hammer and the scrapper.
Furthermore, they said since u r doing reno, u are the cause of it, so u(ya that's u, Bro) should pay half of the cost.