[SOLVED] Access Point in plaster

Solution
Everything seems to block wifi technically even the water in the air. Not a optimum option but it still should work when you consider the almost every ones walls are made from some form of plaster and the wifi works ok.
access point embedded in the plaster as well as luminaries, does it harm the signal?
You should look (if possible) at the radiation patterns of the access point. Many of them are intended for ceiling mounting. If that type AP is mounted on a wall most of the signal radiates up and down. If you want to wall mount, then get an AP that was designed for wall mounting. Something like the Ubiquiti in-wall units.