Working with Plasterboard - cutting and fixing
1. A straight line.
Use a pencil to mark on the front (white) side of the plasterboard where you want to cut it. With the plasterboard sheet flat on a firm surface, lay a steel straight edge against the marks (hold the straight edge on the piece of plasterboard that you want to use so that if your knife runs off line, it will go into the waste material) and firmly draw a craft knife along the straight edge cutting both the paper covering and into the plaster.
- Turn the sheet onto its edge and give the board on one side of the cut a sharp push towards the back of the plasterboard. One
problem with this method is that a 1.2m wide sheet may sag, so getting a clean, sharp push may be difficult.
- Move the sheet so that the backing is against a flat surface and with the cut line over an edge, then give the part of the board extending over the edge, a sharp push towards the back.
Whichever method is used, the plaster core should break fairly cleaning and then it is just a case of slicing through the grey backing along the line of the break with a craft knife.
Remove any paper burrs using fine sandpaper.
2. A cutout
For an 'L' shaped cutout, draw the lines on the front paper and drill a small hole (slow speed) through the plasterboard where they meet.
With the sheet on a firm flat surface and using a steel straight edge as a guide, cut from the hole to the edge of the plasterboard along each line in turn using a craft knife, again hold the straight edge on the piece of plasterboard that you want to use so that if your knife runs off line, it will go into the waste material.
Now cut the plasterboard across the waste along a line bisecting the two previous cuts from the hole to the edge of the plasterboard. Repeat this cut further into the plasterboard, turn the plasterboard over and cut through the backing paper along the line.
You now effectively have two triangular pieces of waste, each attached by one edge to the plasterboard you want to use. Firmly hold one of the pieces of waste and pull it sharply towards the back of the plasterboard, the plaster core should break cleanly and then cut through the backing paper to detach the waste piece. Repeat with the other piece of waste.
You may find that the plaster core has not broken cleanly near where the two lines meet, you may need to tidy this up using the craft knife.
Remove any paper burrs using fine sandpaper.
Other shapes can be cut out using variations on the above, where an enclosed hole is required in a plasterboard sheet (such as for around an electrical socket), this can be cut out using a fine toothed padsaw having first drilled a shall hole in each corner and a larger hole in the waste to accept the pad saw blade.
Plasterboard should be positioned with a small gap between each sheet - no greater than 3mm.
There are two options when fixing plasterboard to stud partitioning, either to use galvanised nails or plasterboard screws. The choice is really personal preference although when cladding both sides of a stud partition, using screws reduces the amount of hammering required.
Whichever method is used, make sure that you know what is behind the plasterboard and avoid pipes, electric cables etc before fixing the plasterboard.
When using nails, they should be galvanised nails, about 30mm (1¼ inch) long for 9.5mm thick plasterboard or 40mm (1½ inch) long for 12.5mm thick plasterboard. Fixing centres should be about 150mm (6 inches). Nails should be hammered home until the nail head is flush with the surface. Care needs to be taken not to over hammer the nails as this can cause the plaster core to break - this is especially important when nailing the edges of a sheet where nails should not be nearer than 12mm (½ inch) to the edge.
Plasterboard screws are usually black with pozidrive, countersunk heads. The screw length should be such that the screw penetrates the timber by about 25mm (1 inch) i.e. for 9.5mm thick plasterboard use 32mm long screws, or for 12.5mm thick plasterboard use 38mm long screws. Fixing centres should be about 150mm (6 inches). These is no need to pilot drill holes when using normal plasterboard and the screws should be screwed home until the head is just under the surface level of the front paper. Care needs to be taken not to over drive the screws as this can cause the plaster core to break - this is especially important when fixing the edges of a sheet where the screws should not be nearer than 12mm (½ inch) to the edge.
Fixing plasterboard to brickwork and masonry is normally done by 'dry lining', this technique involves the application of 'dabs' of plaster adhesive to the wall and then the plasterboard is bedded onto them. The full technique will be explained elsewhere.