How to Repair Plaster Mouldings
Cornices are fitted to cover the gap between wall and ceiling. With an ornate plaster cornice, you may want to dig out the encrusted paint to reveal the original profile; a small pointed stick and lots of water will do the job, but be patient – it will take time.
Adding a cornice is a simple job if you use one of the modern lightweight polystyrene mouldings (these are simply glued into place), but fitting traditional plaster mouldings requires more care. It is probably best to fit the cornice prior to decorating. You will need to cut the required mortices at internal and external corners in addition to using adhesive, which needs to be applied on the two sides of the curve, you will normally have to drill holes in the plaster moulding to fit screws into the wall after pushing it into place. You need to clean off the excess adhesive and make good any gaps between the cornice and the wall with plaster filler.
Dado rails are traditionally positioned at waist height around a room to protect the wall from damage caused by chair backs. Adding a dado rail can be easy if you use one of the timber mouldings that are fitted by a clever click-on system, otherwise you will have to screw sections of timber moulding on to a completely flat wall. Any dips can be filled beforehand and sanded for a smooth surface.
These come in choice of polystyrene or plaster. Polystyrene ceiling centres are easy to fit, requiring only adhesive. Plaster ceiling roses are relatively heavy, so need to be held up with screws driven up into the ceiling joists, as well as adhesive; otherwise the whole lot might come crashing down! You will need to establish the position of these joists with a joist detector before fixing the ceiling rose.
Find the centre of the ceiling by using two lines of string stretched diagonally from opposite corners of the ceiling. Mark the position of the ceiling rose on the ceiling by drawing round it with a pencil, centred on where the strings intersect.
Seal the ceiling and the back of the rose with a coat of dilute PVA adhesive. Apply some plaster or tile adhesive to the back of the rose, then press firmly into place. Wipe off any excess glue. If you have a central ceiling light, make a hole in the ceiling rose and pull the lighting flex through before fixing the rose. Paint the ceiling rose to finish.