Home Decorative coving

Materials

Coving is available in three materials: gyp(the same substance as plasterboard), expanded polystyrene foam, and timber. Timber coving, which also has other uses in carpenty and joinery, is known as scotia.
The most commonly used type is gypsum coving. This is hard, and so unlikely to be damaged, and can be expected to last for years. It is also, and perhaps surprisingly, slightly flexible, so that it can be curved to fit against an out-of-true ceiling. Gypsum in long strips is, however, easy to snap, so that you have to be careful carrying it about. It should be carried on edge to resist the pull of gravity.
Gypsum coving can be fastened on with either adhesive or screws, as described below. Its price is between that of the other two types.
Expanded polystyrene coving is very cheap and light, flexible and easy to put up with adhesive (though it should not be nailed or screwed). When properly installed, its appearance is as good as that of any other type. But it does have disadvantages. The foam plastic it is made out of is easyto dent and chip,so great care has to be taken not to damage it when carrying it and putting it up. For the same reason, it cannot be fixed with nails or screws; and when you change your wallpaper, stripping off the old paper will probably damage it so much that it has to be replaced. The surface is attacked by cellulose and spirit-based paints (though in practice, no ordinary decorating paint is of this type).
Timber scotia is the most robust type of coving, and also the most expensive. It is, obviously, not fragile. It can be nailed or screwed on, which makes it suitable for fixing to stud walls and saves you from having to use messy adhesive. This type of coving makes a perfect finish for the top of timber-boarded walls; it can be used to hide any gaps between the tops of the boards and the ceiling, and it can be varnished to match the rest of the wood.
Gypsum and expanded polystyrene coving are sold by DIY shops in make-up packs containing various lengths, and can be bought by the yard from builder's merchants. It is normally 4in. or 100mm wide, though 5in. or 125mm wide coving suitable for larger rooms can generally be ordered from builder's merchants only.

Preparations for fixing

The surfaces that coving is to be fixed to must always be marked out and prepared in a suitable way for the fixing method you plan to use.
It is particularly important to remove anything underneath the coving that would stop it from being fastened on properly. Normally, you will be installing the coving at the same time as you are redecorating the room, so you will be stripping off old wallpaper anyway. But if you are putting it up later, and planning to stick it on with coving adhesive, all old wallpaper should be stripped right down to the plaster.
To do this, you have to know exactly where the coving is to go and how far it will reach across the ceiling and down the walls. This applies equally to coving fixed on with nails or screws, and the walls and ceiling should be marked out in the same way in each case.
Standard 4in. or 100mm wide coving reaches 28in. or 71mm from the corner of ceiling and

wall in both directions. So a line this distance from the corner should be drawn along both wall and ceiling wherever the coving is to be fitted. This is slightly more complicated than it sounds, since walls and ceilings are hardly ever quite straight.
The method you use to mark the lines depends largely on how irregular the walls and ceiling are. If they are very lumpy, as they might be in an old house, the coving will not fit right into the corner and will have to be set on top of the most prominent parts and the gaps behind filled with coving adhesive. In this case, the chalk line method described below should be used to draw a perfectly straight line.

If, however, the walls and ceiling are smooth but just slightly out of true, the coving should be fitted along this gentle curve for the best appearance. If you want to do this, scribe a line a constant distance from the corner with a pencil and wood block cut to the correct thickness.
If the walls and ceiling are both grossly irregular and thoroughly out of true, coving is probably an unsuitable finish for your room and you should use another finishing method that disguises the top corners of the room, such as finishing the wallpaper a few inches below the ceiling and trimming its top edge with a strip of narrow wood bead to look like a picture rail.

To mark a wall with a chalk line, take a piece of string at least as long as the wall and chalk it thoroughly with chalk of a colour that will contrast with the wall (you can buy coloured chalk powder from DIY and hardware stores). Then, in the case of a perfectly straight and true ceiling, mark a line down the wall at each end 28in. or the appropriate distance down from the corner at each end. If the ceiling is irregular, mark points 28in. below each of the most prominent lumps, directly under them on the wall whereverthey occur.
Now get somebody to help you. He or she should stand at one end of the wall, holding the end of the string. Now go to the other end of thewall with the other end of the string, and (for a straight, regular wall) get your helperto hold the string firmly against the mark. Stretch the string taut and hold your end against your mark, then reach towards the middle of the string with your other hand, pull it out a couple of inches and let it snap back against the wall, marking a neat, perfectly straight chalk line.

In the case of an irregular wall, the string should be adjusted so that it falls on the most prominent lumps, and so follows the line the coving will actually take. In either case, the chalk line should immediately be pencilled in along a straight edge before it is smeared, and the ceiling should be marked in the same way.
If you plan to fix your coving on with adhesive, all wallpaper, flaking paint or soft distemper should be removed from between the lines, and the surface well scratched with a special scratcher or an ordinary fork to provide a 'key' for the adhesive. Then any resulting dust or loose particles should be brushed off.

To support the coving while the adhesive is drying, temporarily nail 6in. (150mm) lengths of batten at 3ft or 1 m intervals just under the line you have drawn on the wall. Use masonry nails knocked in part of the way, so that they are easy to remove.
If the coving is to be screwed on to a masonry wall, drill holes and insert fibre wall plugs at 1 6in. or 400mm intervals along the wall and a minimum of ;in. (19mm) from the pencil line. Also drill and plug holes in the ceiling at twice
this distance from each other and the same distance from the line.

Cutting and jointing

All types of coving should be cut with a very fine-toothed saw; a tenon saw is ideal for straight cuts, and a coping saw for the curved cuts that are needed for scribed joints. The coving should always be cut to the exact length of the wall before it is put up. On long walls, you may have to joint it somewhere along its length; the coving should be cut straight across to make a simple butt joint, which can be disguised by filling it with coving adhesive or cellulose filler. Always saw with the front of the coving facing you.
Inside corners should be formed by first cutting both pieces to the full length of the wall they lie against, then scribing one of them to fit the other as described for skirting boards in 'Marking for a true fit'

Outside corners, for example at the front corners of chimney breasts, should be mitred, using a tenon saw and a carpenter's mitre block (available very cheaply at DIY and hardware stores) to get the angle right. The length of the wall should be marked on the back of the coving; this mark should then be lined up against the appropriate 45' slot on the mitre block, making sure that the coving is properly angled into the corner of the block as it will lie against the wall (but the other way up).

Make absolutely sure that the coving and the slot are the right way round, then insert the saw blade in the slot and cut down into the coving, using a light pressure. The pressure should be particularly light in the case of polystyrene foam coving, which is easy to chip and tear.
If you have bay windows in your house, you will be faced with the difficult problem of cutting coving to fit around corners not at 90% both inside and outside. The way to do this is to mark the angle directly from the walls. First draw your pencil lines along the walls as accurately as possible-along these short runs, the chalk line method should not be used; just use a rule. Then, at each corner, draw a line straight out from the corner of the walls to the intersection of the pencil lines.

You can now transfer the angle directly on to the coving by holding it up in place and marking the position of the angle of the walls on to the back, and of the intersection of the pencil lines on to the front. Prop the coving up at the correct angle and hold the saw blade above it so that it lies between the two marks, then cut carefully straight down.
Inside corners should be cut before outside corners by this method, but for a piece of coving that runs between two inside corners, you will find it impossible because you can't hold an over-length piece up into the space. To overcome this, mark the angle of the walls on to a cardboard template, and use this to mark the coving.Great accuracy is not essential in cutting joints, because any gaps can be filled with adhesive or filler.

Sticking on coving

Coving adhesive is a stiff white adhesive
with very good gap-filling properties. It also dries quickly; this is deliberate, to stop the coving from falling off while the adhesive dries. But it does mean that you have to work very fast-most types only stay workable for 15 minutes. Gypsum coving adhesive comes in the form of a powder to be mixed with water. The type for polystyrene isgenerally ready- mixed. Both, however, are used in the same way.

Before starting work, ensure that all the lengths of coving are cut to length and arranged so that you can pick up the right one quickly, and that the wall and ceiling are fully prepared as described above. Damp the plaster to make the adhesive stick better. Have by you a square-ended metal spatula or cook's palette knife and a more flexible tool of the same shape such as a rubber saucepan-cleaning spatula or a plastic spatula fo the type supplied with some brands of cake mix.Now mix the adhesive if it needs it and spread it generously between the lines marked on wall and ceiling, using the metal spatula as if buttering bread. The more irregular the wall, the more adhesive you should put on. Don't mix more adhesive than you need immediately, or it will just dry up.

Press the lengths of coving into place, pushing them gently into the adhesive so that a little of it is squeezed out above and below. Then scrape along the top and bottom quickly with the metal spatula to remove excess adhesive; this can be pressed into the joints. Never mind about the sections covered by the supporting battens, because the battens themselves will shape the edge of the adhesive. But clean up the open sections thoroughly, as the adhesive dries very hard and is difficult to sand down. Still working fast, finish off the ragged edges of the adhesive by smoothing them with the flexible spatula. This completes the job, and you can paint the coving as soon as the adhesive dries.
Screwing or nailing coving.

If you plan to screw on your coving, cut each section to exact length as described above, then hold it to the wall just below the pencil lines and transfer the position of the fibre plugs accurately on to the coving. Repeat this for the plugs in the ceiling.
Now drill the coving to take your screws, which should be about 14in. or 30mm long. Use a drill -countersinker if possible and counterbore the coving so that the screw heads can be sunk completely below the surface. This will make it possible to fill over them invisibly. Make sure that the holes are drilled at the right angle, so that they will sink straight into the wall plugs at right angles.
It is a wise precaution to use sherardized or japanned screws, since any moisture in the walls might cause rusty marks to appear above ordinary steel ones.

When all the holes are drilled, simply screw the coving in place. Then fill over the screw heads, and also fill any gaps behind or above the coving, with cellulose filler. Coving adhesive can also be used and is probably better, because it is stronger when it dries.
Coving can also be nailed if there is a suitable backing to nail it into (though polystyrene foam
coving cannot be either nailed or screwed).

This method may be found convenient in a stud wall ; you can nail the coving to the studs in the wall and to the ceiling joists, both of which will usually be found at 16in. or 400mm centres. Drill test holes where the coving will later hide them to confirm this. Mark the position of the studs and joists lightly on the wall and ceiling in pencil outside the marked lines for the coving.
Nail the coving in place with 1;in. or 30mm small-headed galvanized wallboard nails in the case of gypsum coving, or sherardized lost head nails of the same size for timber scotia. Punch the heads below the surface (on gypsum, great care must be taken) then fill over the heads and behind the coving where there are gaps as before.


Other uses for coving

Gypsum coving has a very useful feature: it absorbs sound better than any other material in the same price range. Flat-dwellers will find it invaluable in the construction of a soundproof ceiling that will work both in absorbing the noise they create themselves and, to a slightly lesser extent, in damping the noise of the people above walking over their floor and moving furniture.
The same technique can be used to create a soundproof wall, though some people may find the rather overwhelming appearance of the coving-covered panels too bold for a wall while it may be acceptable on a ceiling.
A cutaway diagram of the arrangement is shown Battens of 2in. x l in. or 50mm x 25mm timber are nailed to the ceiling at 20in. or 500mm centres, preferably across the line of the joists as this will make them easier to fix. It this is not possible, you may have to plug and screw them to the plaster between the joists.

Fibreglass insulating blanket of the type used for lofts is then laid between them and supported by strips of dark-coloured hessian or some similar cheap, open-weave fabric tacked to the battens. Finally, the coving is nailed across the line of the battens with its flat, chamfered back resting against them. There should be a gap of ;in. (19mm) between each piece of coving for the best sound insulation.
Coving of any type also makes an attractive cornice to trim the top of a wooden pelmet. If used this way it should be nailed on through its lower edge only, so that it is fastened in the same position as if it rested against a flat ceiling.

Gypsum coving, which is completely noninflammable, can be fastened to the wall a short way below the ceiling with fluorescent tubes inserted in the triangular space behind it so as to be invisible from below. This gives a very soft indirect lighting in a room, since all the light that reaches the room is 'bounced' off the wall and ceiling first.

Don't use any other type of coving for this and make sure that the light fitting doesn't touch the coving at any point.
Coving is also useful for covering pipes and cables running down the corner of the walls of a room. If painted or papered to match the walls, it makes an unobtrusive alternative to ugly pipework. Only gypsum or timber should be used for this, as polystyrene foam is too easily dented to use below head height.

Home Decorative coving