Fitting Corner Beads - Vertical Edges of Corners or Around Windows

All corner beads do roughly the same job. They differ in material and in which layer they belong to. The choice always depends on the background and the conditions in the room.

Galvanised steel angle beads

A perforated profile made of galvanised sheet steel. It is mainly used in traditional lime, cement or gypsum plaster indoors. It is stiff, holds a line well and copes with hallways and stairwells where corners get knocked often. It is usually not chosen for damp rooms or outdoors: if the zinc coating gets damaged, the steel can rust over time and the stain can come through the paint.

Aluminium corner beads

Aluminium does not rust like steel, and it is light and fairly rigid. Aluminium beads are used on plasterboard and under skim coats, especially on long or heavily used corners where an accurate line over the full wall height matters.

PVC corner beads

PVC beads are more flexible, never rust and are easy to cut. They suit flats, corners that do not take many knocks, bathrooms and detailed plasterboard work such as niches and shelves. Under a hard knock they tend to bend rather than keep a perfectly sharp edge.

Corner beads with mesh

A PVC or aluminium profile with glass-fibre mesh attached. The mesh is bedded into adhesive or base coat and also reinforces the surface around the corner. These are typical for external wall insulation and window reveals. Outdoors, use the profiles the insulation system manufacturer approves for that system, not ordinary interior beads.

This job can mean two slightly different things, so it is worth knowing which one you are being offered.

• Fitting corner beads means setting the profile into fresh plaster or adhesive and lining it up. The bead then guides the next coat of plaster, which the plasterer or decorator applies as a separate step.
• Fitting and filling aluminium or PVC beads also includes filling the bead flush with the wall, usually in two or three thin coats, and a light sanding. The result is a corner ready for primer and paint. This version is common on plasterboard and under a skim coat.

When you compare quotes, check whether the tradesperson includes only fitting the bead, or filling and sanding as well. The difference in work is considerable.

The condition of the corner matters most. A straight, solid and clean background goes quickly. An old corner with loose plaster, layers of paint or a big lean out of vertical has to be knocked back, consolidated and built up first, which adds time and material.

• Height and length of the corner: an ordinary wall in a flat can be done from the floor or a small stepladder, while a tall stairwell or gable needs scaffolding.
• Number and type of corners: one long straight corner is quicker than lots of short edges around windows, niches and recesses, where beads have to be cut and joined precisely.
• Background: plasterboard needs fine filling in several coats, while plaster needs accurate guiding and control of thickness.
• Required surface quality: under a sheen paint or with side light from a window, the transition over the bead has to be flawless, otherwise it will show.

If you have a few corners at normal room height and the background is sound, you can do this yourself. You will need a spirit level or a long straight edge, tin snips, filling knives, a filler suitable for your background and a sanding mesh. Leave facades and work at height to a professional.

1. Remove loose plaster, dust and flaking paint from both sides of the corner.
2. Prime the corner as recommended by the filler manufacturer and let it dry.
3. Measure the height of the corner and cut the bead slightly shorter, so it does not press against the ceiling or floor.
4. Apply filler to both sides of the corner along the full length, not just in dabs.
5. Press the bead into the filler until it squeezes through the holes, then set it plumb with the spirit level.
6. Scrape off the excess filler and check the line straight away with the straight edge.
7. Once dry, apply a second, wider and thinner coat that covers the bead and feathers out onto the wall.
8. Apply a third finishing coat if needed and, when dry, sand lightly without exposing the nose of the bead.
9. Dust off, prime and only then paint.

• A crooked bead: if it is not checked with a level, the corner may look straight at first, but after painting every wave shows up in light and shadow. Filling will not fix a crooked bead.
• Voids behind the profile: with dabs of filler or weak pressing, hollow spots stay behind the bead. A knock then breaks the edge and the filler cracks around it.
• Thick coats in one go: thick filler shrinks and cracks. Thin coats with drying time as the manufacturer states work better.
• Sanding through to the metal: an exposed bead nose shows through the paint, and with aluminium or galvanised steel it can leave a dark line.
• The wrong material: an interior bead on a facade, plain steel in a damp room or a filler not suited to the background.

When you take over the work, look at each corner from the side in daylight and hold a long straight edge against it.

• The corner is plumb over its full height and the straight edge shows no gaps or waves
• The edge is sharp and runs evenly, with no nicks or dips
• The bead does not stick out or show through the filler anywhere
• Tapping the corner gives no hollow sound
• The filler blends smoothly into the wall with no visible band
• There are no hairline cracks along the bead
• At windows and doors the bead joints are clean and in line
• The surface is dust-free and ready for primer and paint