Plastering to Guide Beads: How Walls Are Made Straight

Plastering to guide beads is the technique used to make walls plumb and flat. Stages: survey, preparation, setting beads, applying plaster and inspection.

A wall that looks straight to the eye and a wall that is straight when measured with tools can be very different. The difference shows up when furniture goes in, tiles are laid, corner profiles are fitted or light falls across the wall from the side. Plastering to guide beads (screeds) is the technique used to make a wall not just smooth but plumb and flat in one plane.

What a guide bead is and why it is used

A guide bead is a profile fixed to the wall that defines the finished surface of the plaster coat. Galvanised metal or plastic profiles are usually used. The beads are set vertically along the wall, parallel to one another, with their front edges in the same plane.

Plaster is filled between the beads, and a long aluminium straightedge is drawn across the beads to remove excess material. The plaster surface therefore follows the plane created by the beads. Without beads, the plasterer levels the surface by eye with a short tool, leaving local waves and bows.

Measuring first

Work begins by measuring the wall. A laser level or plumb line reveals how far the wall leans, and where the hollows and bulges are. This answers two questions:

• what the minimum and maximum plaster thickness will be;
• which mix and how many coats are needed.

If the highest point of the wall leaves no room for a plaster coat, that area is sometimes cut back. For very large deviations, plasterboard lining may make more sense than plaster. Measuring all the walls of a room together is also important for getting square corners.

Surface preparation

Plaster adhesion depends on how the substrate is prepared:

• old, weak and crumbling plaster, paint, dust and dirt are removed;
• metal elements are protected from corrosion and protrusions are cut back;
• the surface is primed with a product suited to the substrate and the plaster mix;
• very smooth concrete gets a bonding primer with quartz grit;
• reinforcing mesh is embedded where different materials meet (brick and concrete, for example) and in zones at risk of cracking.

Electrical cables, socket boxes and plumbing outlets are installed before plastering, with box fronts set to the future plaster surface.

Setting the beads

Setting the beads is the most precise stage of plastering. They are aligned vertically with the laser beam and fixed to the wall with small dabs of the same mix. The spacing between beads is chosen slightly shorter than the straightedge so that it always rests on two beads.

Once set, the plane of the beads is checked again with a long straightedge or laser. The beads are not touched until the fixing mix has hardened, or they may shift.

Separate corner beads are used for external corners. They create a straight arris and protect the corner from knocks. Beads are also placed at window and door reveals so that the reveal meets the wall at the correct angle.

Applying and levelling the plaster

The mix is applied between the beads by hand or by machine, then the straightedge is drawn upwards from the bottom, resting on the beads. Gaps are filled and the straightedge is drawn again. Once the plaster has firmed up slightly, the surface is trowelled or dampened and polished according to the manufacturer's method.

What happens to metal beads is a separate issue. In cement plaster or damp rooms, galvanised beads may eventually cause rust marks, so it is often recommended to remove them once the plaster has set and fill the channels. Plastic beads reduce this risk. Which approach will be used should be agreed with the contractor in advance.

Inspection

The wall is inspected after the plaster has dried and before skim coating. Check:

• how large the gap is under a two-metre straightedge placed at different points and in different directions;
• how far the wall deviates from vertical;
• whether corners are square and arrises straight;
• whether there are cracks, voids, detached areas or rust marks.

The acceptance tolerance (the permitted deviation) should be written into the contract or project in advance. Stricter requirements apply if tiles, concealed doors or fitted furniture against the wall are planned.

In apartment and office renovations Zaferoğlu İnşaat prepares walls and ceilings to suit the finishes specified in the project. Requirements for wall flatness can be defined in advance together with the renovation plan.