Plasterboard is usually employed to make new ceilings, but it can also be used to replace an old lathand-plaster ceiling which has deteriorated beyond repair.
Fixing the plasterboard in place and finishing its surface ready for decorating can be tackled by a competent amateur, but applying wet-plaster to a boarded ceiling should be left to a skilled tradesman — it is strenuous work and extremely difficult to perfect.
Start by stripping away all the old and damaged plaster and laths, and pull out all the nails.
This is a messy job, so wear protective clothing, a pair of goggles and a face mask while working. It is also a good idea to seal the gaps round doors in the room to prevent dust escaping into the rest of the house.
You will need to dispose of a surprising amount of waste material, so have a number of strong plastic sacks available to make it easier to handle, and hire a skip to have it removed.
If necessary, trim back the top of the wall plaster so that the edge of the ceiling plasterboard can be tucked in.
Inspect and treat the exposed joists for any signs of woodworm or rot.
FITTING NEW BOARDING
Measure the area of ceiling and select the most economical size of boards to cover it.
The boards should be fitted with their long paper-covered edges running at right angles to the joists. The butt joints between the ends of the boards should be staggered on each row and supported by a joist in every case.
Skew-nail perimeter noggings between the joists against the walls, and fit intermediate ones in lines across the ceiling to support the long edges of the boards. It is not always necessary to fit intermediate noggings if the boards are going to be plastered, but they will ensure a sound ceiling. The intermediate noggings should be at least 50mm (2in) thick and should be fitted so that the edges of the boards will fall along their centre lines.
If necessary, trim the length of the boards to ensure that their ends fall on the centre lines of the joists.
Start fixing the boards, working from one corner of the room. Plasterboard is a relatively heavy material and it normally takes two people to support a large and awkward sheet while it is being fixed . However, if you have to work on your own, use support battens and props, called ‘dead-men’, to hold the boards in place while you are nailing them (see far left).
Make a pair of props that are slightly longer than the overall height of the room (1) from 50 x 50mm (2 x tin) softwood. Nail a cross piece and braces to one end of each prop. You will need to nail a 50 x 25mm (2 x 1 in) temporary batten close to the top of the wall to support the long edges of the first row of boards (2). Supportthe next row with a batten that overlaps the edges of the first boards and is nailed to the joists (3). Fit packing under the batten to provide the necessary clearance for the new boards.
Use galvanized plasterboard nails to fix each board, working from the middle outwards and nailing at 150mm (6in) centres. This prevents the boards from sagging in the middle, which is likely to happen if their edges are nailed first.
If the boards are to be plastered, leave 3mm (Vein) gaps between the cut ends and the paper-covered edges. For direct decoration, however, butt the paper-covered edges, but leave 3mm (1/4in) gaps at the ends of each board.
Finish the joints, using this method:
A plaster cornice or a simple caving are used to finish the edges of a ceiling where it meets the walls. Ready-made gypsum coving is widely available, generally in a fairly limited range of profile sizes and in various lengths. However, you can buy any number of period-style fibrous-plaster cornices, many of which are exact copies of Georgian and Victorian originals.
This sequence describes how to make a coved ceiling, but you can use the same method to fit a cornice.
Start by marking parallel lines along the wall and ceiling, setting them off from the angle at the distance specified in the manufacturer’s instructions, then scratch the plastered surfaces within the lines in order to provide a good key for the adhesive (1).
Measure the wall and cut the coving to fit, using the template to saw the mitre . Remember that when you are cutting mitres for outside corners, the coving must be longer than the wall, and must extend up to the line of the return angle drawn on the ceiling. Cut the coving with a fine-toothed saw, sawing from the face side.
Prepare the special adhesive by mixing the powder with clean water and stirring it to a creamy consistency. The adhesive should remain usable for about 30 minutes, but it is best to aim at making just enough for one length of coving at a time. Use a filling knife to apply the adhesive liberally to the back faces of the coving which will be in contact with the wall and ceiling.
Templates are sometimes provided by the makers which are intended to be used as guides when you are cutting the internal and external mitre joints.
Dry, bare plaster must be dampened just before the coving is put in place. Press it into the angle and level it with the guidelines (2). If a piece of coving is more than about 2m (6ft 6in) long, two people should fit it. Should it tend to sag when in place, support it with a couple of nails driven temporarily into the wall under its bottom edge and remove them when the adhesive has set.
Scrape away any beads of surplus adhesive before it sets and use it to fill the mitre joints as the work progresses. Use your finger to apply the adhesive to internal mitres if you find it easier, but finish off all joints with a filling knife to leave a sharp corner (3).
Wipe along the edges of the coving with a damp brush or sponge to remove any traces of adhesive. When it dries, prime the coving for painting.
Some makers of plaster coving and cornice supply a cardboard template with their product, which enables you to cut mitred corners more easily.
Mark the coving or cornice to length on one edge, bearing in mind whether you are mitring for an external corner or an internal one. Trim and fold the template and place it over the coving in line with the measured mark, then press it down so that it moulds itself to the curve of the material. Use the appropriate edge of the template — for an external or an internal mitre — and, with a soft pencil, draw the cutting line along it on the face and edges of the coving, tracing the template’s edge.
Cut the mitre with a fine-toothed saw, following the marked angle.
If you use plaster coving or cornice right through the house, it is worth making a mitre block as a jig to help you cut the joints accurately.
Cut a baseboard from 18mm (3Ain) plywood or chipboard about 200mm (8in) wide and 450mm (1ft 6in) long. Cut a piece of 100 x 50mm (4 x 2in) planed softwood to the same length for a fence.
Glue the fence to the baseboard flush with one long edge. When the adhesive has set, mark out and make three saw cuts, one at right angles to the face of the fence and two at 45 degrees in opposite directions. Nail a stop batten to the baseboard at a distance from the fence which will allow the coving to fit snugly between them for cutting.
The baseboard of the mitre block represents the ceiling and the fence represents the wall. Lay the coving in the jig with the end to be cut in the right direction for either an external or an internal mitre.