Replacing an old plasterboard ceiling is a messy task, but can often be necessary one. Ceilings, especially those on the ground floor, can be subject to a lot of stresses over time and can often crack. You can patch smaller cracks with filler, but if the cracks are being caused by an underlying problem, this will only be a short-term fix. You can read more on filling cracks and holes in plaster here.
Removing the Existing Plasterboard
As we have mentioned, removing an old plasterboard ceiling is a messy and dusty job, so a mask and goggles are essential. Clear the room you are working in and open all the windows and external doors. If possible, keep internal doors closed to stop dust and debris spreading to the rest of the house. Ideally work like this should be done before any carpets are laid, but if they are already down, cover them with dustsheets. Using a chisel or crowbar, make holes in the plaster to locate the joists. It is likely that the old ceiling will be lath and plaster, so start to pull the laths free of the joists and let them drop to the floor. Make sure you remove any nails from the joists, and then inspect them for damage or rot, etc. Assuming they are all sound, you are ready to start fixing the new plasterboard.
Preparing to Fix New Plasterboards
If your joists are up to 450mm apart, you can use the thinner 9.5mm plasterboard, if the joists are further apart, it is better to use the thicker 12.7mm boards to avoid sagging. If you are replacing the plasterboard in a top storey room, consider buying insulated plasterboard. Fitting plasterboard alone is a hard task, so get someone to help you. However, even with an extra pair of hands, it is a good idea to make yourself a “deadman”. This is a piece of batten, etc, slightly longer then the height of the room with a cross member nailed to the top to form a T shape. This can be used to hold the plasterboard in place after you have lifted it up against the joists. Alternatively, you can hire a Panel Lifter from most hire shops. Panel Lifters can also be used to hold plasterboard sheets whilst they are fixed to walls and sloping ceilings.
The First Board
Start in a corner of the room and with your helper and the Deadman ready, lift the first board up against the joists and slide it firmly into the corner. Use your Deadman to hold it in place and start to nail it to the joists using galvanised plasterboard nails. Leave a 3mm gap between this and all subsequent boards.
Plasterboard nails have a jagged shank to grip the material and are coated in Zinc to stop corrosion. If you are using the thinner type of plasterboard, you can safely use 30mm nails. The thicker type of board will need 40mm nails. Once a board is in place, start nailing the board to the joists in the middle. Working your way out to the edges in this way will help to avoid sagging in the boards. Space the nails out by about 150mm all the way along the joist. The boards should always end in the middle of a joist to give the ends support. Try to keep any nails at least 13mm back from the edge.
Filling the Joints
Once you have all the boards firmly nailed in place, you need to start filling the joints. For this you should use joint filler covered with 53mm paper jointing tape (both available from all good DIY stores). Mix up your filler and apply in a continuous band (about 50mm wide) all the way along the joint. Now apply the paper over the top and press it firmly onto the filler. Smooth this out, taking care to squeeze out any air bubbles. Leave it to dry for a while and then apply another layer of filler over the top to hide the tape. When this has stiffened slightly, smooth the edges of the filler with a slightly damp sponge and then leave it to set fully. You then need to apply a very thin coat of joint finish (again, available from most DIY stores) over the joint, using a metal plasterers trowel to get a nice flat finish.
Before the joint finish has completely hardened, you need to smooth the edges. You can either use a purpose made tool for finishing joints or a smooth plastic sponge. Use circular motions to spread the almost dry finish to a very thin layer. Let this set and apply a second layer. Repeat the smoothing steps above once this is partially set. The final thing to do is fill the holes made by the nails. Apply the filler and when it has set, apply a thin coating of finish over the top. Feather this off with a damp sponge as before.
Covering Gaps Between Wall and Ceiling
Whilst you should try your best to avoid leaving gaps around the edge of the ceiling where it meets the wall, if you do find that you have cut a plasterboard slightly too short or nailed it in slightly the wrong place, you don’t have to rip everything down and start again. The simple solution is to fit coving around the room to cover the gap. Coving is available in several types (including wooden, plaster, polystyrene and plastic) and is very easy to fit. It covers a variety of sins and will add a bit of character to your room (particularly nice if you live in a modern house). You can read more about fitting coving in our guide here.