Fixing Cornices to Plastered Walls and Ceilings

It is important that you always have the cornice the right way round when preparing it for fixing. Two things you have to be aware of are; the wall line and ceiling line. When setting out, the first thing you need to do is find out how far the cornice sticks out by placing a square against the ceiling and wall line. The distance between the square and the the outside edge of the ceiling is measured to find out how far the cornice sticks out. Make a marking at either end of the cornice and then use a chalk line to mark out between both of these points, this then needs to be done on every wall. Cornices should be cut to a mitre, but it will have to be reinforced so that it does not crack so the mitres do not need to be very tight. After the projection lines have been marked out onto the ceiling, you can draw a line between the angle on the wall and the point where the projection line meets it to work out the mitre lines. The cornice can be placed against the projection line and with two markings, you can mark the mitre lines onto the cornice. One mark is where the mitre line and ceiling meet, the other mark is where the mitre line meets the wall line. This method can be used on any type of mitre. To cut mitres, squares should be secured on to the bench you are using to cut the mitres in a position where the cornice is able to rest against them. Some wood should then be fixed in front so that it is unable to be moved. Once the cornice is against the the square supports and the mitre has been marked for cutting, you can start to cut using a saw. When cutting the mitre, make sure the saw is kept upright and goes straight through the marks. The cornice should never be cut if it is laying flat because otherwise you will end up with a very wide angle. Another way of cutting straight cuts and 90 degree angles is to use a box that is made for individual cornices. The box should be made and measured to ensure it is the perfect size. If it is too big, the cornice will move around while cutting. Stopped end mitres are cornices that are stopped with a straight cut and are generally found where there are staircases that come through the ceiling. When making a short return, it is better to finish with the external mitre cut and placed on the ceiling line. The self return is then fixed to the back of the cornice. To make the self return lie flat on the wall and ceiling, it must be cut in line with the back of the cast. Although there are easier, modern methods, you may sometimes be required to use traditional methods when fixing the cornice. The cornice can be fixed in position once the mitres have all been cut and the setting out is completed. The fixing points can be marked with a pencil on the wall and ceiling. Working on your own will be difficult when fixing the cornices because you have to drill and plug the wall and mark the cornice where it lines up with the holes. Blocks of wood can be used to hold the cornice in place, or for smaller/lighter casts, you can nail them for short periods of time. You can then screw the cornice in place. Fixing blocks can then be removed once the cornice has been cut and fixed in place. It is not always easy to be able to get a fixing point, so to resolve this you may need to cut holes that are big enough to get your hand through in the ceiling board. A wad is soaked in plaster and passed through the hole in the ceiling boards on the back of the cast and onto the plasterboard. The holes can be repaired once the wads have completely set. Another way to fix cornices, dado rails and other light weight mouldings is to use a variety of fixing adhesives. One adhesive that can be used is tile adhesive. The only thing with tile adhesive is that it needs to be supported until the adhesive dries. A deep cross key needs to be made on the background for the backs of smaller mouldings to be fixed to. Casting plaster can be used to fix smaller mouldings too. The material must become cream like, so it should be mixed and then left to stand for a while, then it can be applied directly to the back of the mould and put in place. It will need to be supported with either nails or blocks of wood until the plaster sets. The moulding should be brushed off to get rid of any dirt and any excess plaster should be wiped away with either a busk or a joint rule.