Plaster beads (guides)

Plaster beads (guide screeds or "tell-tales") are guides (metal, plastic or mortar) set to level and plumb before plastering or screeding. They fix the plane and the layer thickness: the straightedge runs along them, the mix is cut level with them, and the result is a flat surface rather than "however the hand went". Plastering and screeding to beads is the quality standard for homes.

How they are set. First the most protruding point of the wall is found and the layer thickness is set from it. End beads are placed vertically at a distance from corners, ceiling and floor, then intermediate ones between them. According to tradespeople, the spacing on vertical surfaces is chosen so that the straightedge rests on two neighbouring beads, and about 30-40 cm is left from corners, ceiling and floor. Verticality is checked with a level, plumb line or laser. Mortar or gypsum mix is applied between the beads and levelled with the straightedge from bottom to top.

Types. Galvanised metal profiles are the most common; they are rigid and hold geometry. Plastic (PVC) beads, including 6 mm high ones, suit thin layers and do not rust. For screed, pipes or profiles on mortar dabs serve as guides. The choice depends on layer thickness, the material (cement or gypsum) and room humidity.

What to do afterwards. Beads should not stay in the layer where they can rust or crack. Metal beads in a damp room rust and can show through paint or filler as stains, so in wet zones plastic ones are better, or metal ones are removed after the mortar sets and the grooves filled. In the brief for rough works we write this point out separately: what is left and what is removed.

When they are needed. If walls are crooked and you need a flat surface for paint, wallpaper, large-format tile or built-in furniture. If the geometry is acceptable, filler or plasterboard on a frame is enough. Plaster to beads is thicker and heavier than levelling with filler, but gives a true plane and saves on later layers. A 2 m straightedge and a level are used to check flatness.

Typical mistakes: setting beads by eye, without level and plumb; too wide a spacing so that the straightedge sags; leaving metal beads in a wet zone; plastering immediately without letting the beads set; not checking the walls after drying. Flatness tolerances depend on the type of finish and are usually set by the technology; without a verified standard we do not quote numbers, and in the project we state flatness requirements in the wall finishes schedule.