If the slopes of the height are about 3 cm, then the putty will not give a good result. In this case, you can not do without a metal and painting reinforcing grid. A painting grid resembling gauze is glued with PVA. The metal mesh is attached with special nails with large hats and is used for the middle layer of plaster (3 — 4 cm). After the putty dries, apply the finish putty layer. With subsequent painting the ceiling, a primer layer is applied. In order to improve the quality of the ceiling repair, it is recommended to use the finishing materials of one manufacturer. This will ensure the «compatibility» of materials.