A GUIDE TO FITTING PAPER BOUND CORNICE
First things first, you need to make the walls and ceiling as flat/level as you can, this can easily be done with some bonding and a feather edge, you might not need to do this on every job but i find when doing a re-skim this normally helps allot.
next thing to do is mark the room out, check the box and it will state the depth and projection of the cornice on the wall edge and the ceiling edge, there are a few different sizes but to make this guide a bit more simple then we will just say that it is going to project 3 inches down the wall and 3 inches into the ceiling.
you then need to ping a line with your chalk line 3 inches down from the ceiling all around the room, you then need to ping a line all around the ceiling 3 inches in from the walls.
now you will need to cut your cornice to size, cut all of the lengths of cornice to the exact size of each wall and try each one op to make sure they fit nice and snug (dont worry about the mitres yet), if you have any external corners the just measure past them by about 5 inches (it would only have to be three inches but if you leave a bit on it will make it easier to cut)
ok now for the mitres.... you can buy a template to do these but i would advise not to as if the walls are not at exactly 90 degrees to each other then you will spend a long time building up the mitres in plaster, so what i like to do is mark each piece of cornice individually as you will always get a better mitre this way. you need to hold the cornice up to the wall, make sure it is sitting perfectly inside the guide lines. then mark the cornice on the ceiling edge where the guide lines intersect (if you are working on an external corner then you will need to mark the wall edge section of the cornice at the point where the wall ends).
now to cut the mitres.... the best way i have found to do this is to build a block for your cornice to sit in whilst you cut it, to do this you will need to nail two short scaffold planks together side by side at a right angle so that it looks like a L shape if you look at it end on (this is an imitation ceiling line). the plank that lays flat is the imitation ceiling and the plank that sits on its side is the imitation wall (when the cornice is in the block it will be upside down)
you might want to read that again just to clarify what i am saying as it is quite hard to explain without diagrams.
now on the imitation ceiling edge of the block you will need to attach a projection rule, so if your cornice projects 3 inches into the ceiling from the wall you will need to attach your projection rule 3 inches in from your imitation wall on your block (the projection rule will be attached to the bottom plank). a piece of roof batten will be fine to use as your projection rule. now when you put the cornice in the block it will lock its self in place under its own weight against the projection rule.
once you have your cornice locked in place just slide one end out and cut through the cornice from the tip of the corner to the mark on the ceiling edge or if it is an external corner you will cut from one mark to the other, be shure to keep your saw plumb when you are doing this.
once you have cut all of your mitres you can start to stick the lengths of cornice up.
first though you will need to prepare the background, where you have marked the ceiling and wall with the chalk line you should go around with a stanly knife and score just inside these lines in a criss cross manner to provide key, then you can start to apply the adhesive to the cornice, you need to apply a bead of adhesive down both sides of the cornice, the section that touches the wall and the section that touches the ceiling, for you to do this the cornice will need to be face down on a bench and and up close to the edge so that you can apply the adhesive with a downward stroke of the trowel without the bench being in the way, then move it to the other side of the bench and apply the adhesive to the other side of the cornice.
the next step is to fit the cornice to the wall, simply push the cornice into the guide lines and scrape off any overspill of adhesive, then wipe it down with a damp sponge. repeat this fore each piece of cornice.
you can start to touch up the mitres now, they should all be quite snug and only need a minimal amount of adhesive to finish them.
on the internals you should use a small tool to push the adhesive into the mitre then use a joint rule to cut it out to shape, then fore external mitres you should use the same technique unly when you are cutting the shape with a joint rule be sure to pull away from the mitre and not into it as the joint rule will pull the adhesive out of the mitre.
NEVER FINISH MITRES WITH A BRUSH! if you aren't happy with them just let them set and go over them again ontitt they are full and true.
this is not the fastest way to fit cornice but it will give you a very good result, although there are many other ways to do this i think that this is the best way as the mitres will not need much work done to them to finish them