Preparing Plasterboard

In your residential or commercial painting job, small cracks, dents, holes or gouges in plaster walls or ceilings can be repaired with interior filler. To search for cracks and gaps that need repairing, hold a torch to the wall and run it over the surface to highlight any flaws that aren’t obvious in natural light. Circle the problem areas with a pencil.

Corner cracks
These cracks tend to indicate movement between the adjoining walls, and require caulking, which is flexible even with a bit of wall movement, preventing the crack from reappearing.
1. Squeeze a narrow bead of flexible gap sealant directly over the crack, around 3 mm in diameter, but don’t overfill as it can make the square corner appear rounded.
2. Mould the gap sealant into the crack with a wet finger.

Nail pops
Fasteners driven too far through plasterboard paper during installation or gaps between the plasterboard and the wall stud can result in nail pops. Movement of the timber makes the Filler over the area pop out from the wall. 1. Add a screw near the first to hold the plasterboard firm. Tap on the pop with the handle of a broadknife to recess a hole,
2. then cover over both nail and screw heads with some wall filler.

External corners
Metal corner angles sometimes pop through the surface plaster. In other cases, vertical hairline cracks form slightly beyond the corner, usually because the angle wasn’t nailed securely or covered in tape.
1. Secure with extra 30 mm plasterboard nails through the loose edges of the corner angle to hold it flat to the wall.
2. Centre tape over the entire length of the angle and cover with two coats of joint compound.

Loose tape
Plasterboard joint tape tends to blister and peel when there isn’t enough joint compound under the tape to anchor it to the plasterboard.
1. Cut and peel the loose tape beyond the evident crack, and fill the hole with fast setting wall filler and leave to dry.
2. Embed a strip of paper tape into the joint compound to cover the patch, then overlay two wide applications of joint compound to blend the patch into the wall.

Damaged areas
If significant damage has been made to a large part of the wall, the damaged area should be skim-coated in a thin layer of joint compound. Begin by removing loose plasterboard poper then prime the remaining raw paper.
Use a brush to saturate the paper with paint and wipe any runs. When dry, lightly sand any raised nubs.
1. Trowel on the joint compound using overlapping vertical strokes.
2. Finish with overlapping horizontal strokes.


Bad butt joints
The joints between plasterboard ends can leave humps caused by poorly feathered edges and build up from badly taped walls.
1. Overlay a wide layer of joint compound to blend the hump with the surrounding wall surface, working from the bottom up.
2. For a clean finish, drag a wide broadknife over the wet compound to smooth the edges immediately after applying the coat of joint compound.
Joint cracks
These cracks usually occur at the corner of windows and door openings, usually the weakest points of the framing.
1. In the centre of the crack, carve out a 10 x 10 mm V-shape with a utility knife, then apply a fast-setting wall filler.
2. Embed paper tape in joint compound, position it directly over the patch then overlay it with two wide layers of joint compound.
There is a range of products on the market, both hand sanding materials and mechanical devices. For hand sanding there are abrasive papers, sanding pads and sponge sanding blocks, in grades ranging from fine to very coarse. Match the grade of paper to the job at hand. Mechanical devices include orbital, belt and disc sanders. Disc sanders are particularly abrasive, and should be used with care.
Many mechanical sanders are fitted with dust collection units.
Scrapers or stripping knives have a flat, slightly sprung blade, which may be broad or narrow. Broad scrapers are used for stripping wallpaper. Other scrapers are used to remove softened paint from flat surfaces.
Tungsten scrapers, shave hooks, with triangular or curved blades set at right angles to the handle, are used to strip paint from moulded woodwork such as window and door frames.
You may be able to buy a scraper with a long handle for leverage and strong, sharp replaceable blades.
Filling knife
A filling knife is like a scraper with a more flexible blade. Use it to press filler into holes and cracks and to level it flush with the surface.
Wire brush

Used to remove loose or flaking material, they are available as a hand tool or as a fitting for an electric drill.
Hot-air guns
Hot-air guns have largely superseded blowtorches to soften paint before stripping. They work like a superheated hair dryer and are much safer than blowtorches as there is no naked flame.
This is the most efficient tool for stripping wallpaper or papered surfaces that have previously been painted over.
It consists of a water reservoir and a hose, which is connected to a steam plate. When the water heats up, steam is forced up the hose and out through the plate. This penetrates the wall covering and softens the adhesive underneath (painted paper must first be scored). Strippers are widely available from hire companies.

Each year thousands of injuries are caused by falls from heights or insecure ladders, rust particles or tile chips flying into eyes or burns from paint stripping chemicals. Wear safety goggles to protect your eyes, wear a face mask if there is a lot of dust; protect your hands with suitable gloves; keep dirt out of your hair with a cap on scarf; and don ear protection for noisy jobs.
Assemble a safety kit before embarking on DIY. For many jobs you’ll need safety goggles and a face mask.