Render and plaster beads explained: types and sizes
On this page
Render and plaster beads are the PVC or metal profiles that form and protect the edges of a render or plaster finish. The five you meet most are angle beads (straight external corners), stop beads (a clean stopped edge), bellcast or drip beads (throw water off at the base), expansion beads (movement joints) and APU or window reveal beads (a neat edge where render meets a frame). The number in the size, 10mm, 15mm, 20mm, is the render depth the bead is built for, so match it to your coat thickness. Use PVC for external and damp work, galvanised steel for internal thin-coat plaster, and stainless for premium or exposed jobs.
What is a render or plaster bead, and why use one?
A bead is a preformed profile you fix to the wall before rendering or plastering. It does two jobs: it forms a straight, accurate edge or corner for you to work to, and it protects that edge from cracking and knocks once the finish has set. Render and plaster are strong in the middle of a wall and weak at every edge and corner, the bead is what makes the edge as tough as the rest.
They come in different profiles for different edges, and in different depths to match how thick your render or plaster is. Get the profile and the depth right and the finish lines are dead straight and stay put. Get them wrong and you are chasing cracked arrises and wavy edges. Here is each type, what it does, and when to reach for it.
What is an angle bead?
An angle bead forms and reinforces a straight external corner (the arris) where two rendered or plastered faces meet. It gives you a crisp, plumb line to rule the finish to, and a hard-wearing nose that shrugs off the knocks a bare plaster corner never would. For internal plaster and thin-coat work you will usually want a galvanised thin-coat angle bead; for external render, a PVC render angle bead in the right depth.
What is a stop bead?
A stop bead forms a clean, stopped edge where the render or plaster ends rather than turning a corner, against a window or door frame, at the top of a rendered panel, or where render meets a different material. It gives the finish a neat, straight termination instead of a ragged feathered edge. Thin-coat systems use a shallow render stop bead; there are galvanised versions too for internal plaster.
What is a bellcast (drip) bead?
A bellcast bead, also called a drip bead, goes at the base of the render, above the damp proof course and above openings. It kicks the bottom edge of the render out slightly and carries a drip groove, so rainwater runs to the edge and drops clear of the wall below instead of tracking back behind the render. It also gives a straight bottom edge and can be run at each storey as a shadow line feature. Our PVC bellcast beads are the standard choice here, PVC because this is exactly where water sits and a steel bead would rust.
What is an expansion bead?
An expansion bead is a movement joint built into the render. Large areas of render expand and contract with temperature, and without a joint that movement cracks the finish. The bead lets the two sides move independently. It must be run over any structural movement joint in the wall behind, and can also be used horizontally as a day-work joint. If you are rendering a big elevation, especially in monocouche or through-colour render, plan the expansion beads in before you start.
What is an APU or window reveal bead?
An APU bead (adaptable plaster upstand), also sold as a window or frameseal bead, gives a neat, protected edge where render or plaster meets a window or door frame. It reinforces the render right up to the reveal so it does not crack or chip along the frame, and many versions carry a mesh flange and a self-adhesive strip with a tear-off bead that leaves a clean shadow gap against the frame. Our APU window beads come with or without the mesh flange, from around £2.10 a length.
What do the bead sizes (10mm, 15mm, 20mm) mean?
The size is the depth of the bead nose, which is the thickness of render or plaster it is built to sit in. So a 15mm bead is made to finish flush with a 15mm render coat. Pick the depth to match your build, not at random:
| Bead depth | Suits | Typical use |
|---|---|---|
| 3 to 4mm | Thin-coat and skim systems | Internal plaster corners, thin-coat render |
| 6mm | Shallow reveal edges | APU window and reveal beads |
| 10mm | Thinner render builds | One-coat and thinner monocouche |
| 13 to 15mm | Standard render build | Two-coat sand and cement, monocouche |
| 20mm | Thick render | Heavy builds, dubbing out uneven walls |
If your bead is too shallow it sits proud and shows through the finish; too deep and the nose is buried and does nothing. Measure your intended coat thickness and buy to it.
PVC, galvanised or stainless: which material?
- PVC / uPVC will not corrode, so it is the safe choice for external render and any damp position, bellcast beads above the DPC especially. Most external render beads are PVC. Browse the PVC plaster and render beads.
- Galvanised steel suits internal thin-coat plaster and skim corners and edges, where it is dry and you want a rigid metal arris. See the galvanised plaster beads.
- Stainless steel is the premium option for exposed, coastal or high-value external work, where you want metal strength with no risk of rust bleeding through the finish. See the stainless steel beads.
The rule of thumb: anywhere it is wet or outside, do not use bare steel, use PVC or stainless.
How are beads fixed?
Two common methods, both fine when done properly:
- Dot and dab in adhesive mortar or render, pressed on and ruled straight, plumb and level, then left to set before you render over.
- Mechanical fixing with a non-corrosive wall plug and screw, especially on bellcast and expansion beads that need to hold a line under their own weight.
Whichever you use, get the bead dead plumb or level and set to the right depth, the finished render follows the bead, so a bead that is out is a wall that is out. Beads come in single lengths (2.4m, 2.5m or 3m) and in trade boxes of 34 or packs of 50 for bigger jobs.
Common mistakes to avoid
- Wrong depth for the render. A 10mm bead in a 15mm coat sits buried; a 15mm bead in a thin coat stands proud. Match the depth to the build.
- Bare steel outside. Galvanised beads in a wet or external position eventually rust and stain the render. Use PVC or stainless there.
- No bellcast above the DPC. Without a drip bead at the base, water tracks back behind the render. Always stop external render on a bellcast.
- Skipping expansion joints. Big render areas with no movement bead crack along the line of least resistance. Plan the joints in.
- Setting the bead out of plumb. The finish follows the bead. Rule every bead straight before you render.
The short version
Angle beads for external corners, stop beads for a clean stopped edge, bellcast beads to throw water off at the base, expansion beads for movement joints, and APU beads where render meets a frame. The size is the render depth, so match it to your coat, and use PVC or stainless anywhere wet, galvanised only for internal thin-coat. Browse the full angle and render beads range, or call the counter and describe the job.
By Steve, Builders Hardware Direct. Steve runs the BHD trade counter and has spent years supplying beads, render and plaster to plasterers and renderers across South Wales. Not sure which bead or depth? Call the counter on 01269 267030 or order online for fast UK delivery.
