How to specify plaster beads
What a plaster bead clause has to say for angle, stop and movement beads inside and out, the decisions behind it, the standards to cite, and how to write it in CAWS and in Uniclass.
Photo: Achim Hering, CC BY 3.0, via Wikimedia Commons.
How do you specify plaster beads?
To specify plaster beads, say which bead goes where (angle beads at external corners, stop beads at abutments and edges, movement beads at control joints, feature beads at openings), give a depth that matches the plaster or render thickness, and choose a material for the exposure: galvanised steel inside, stainless steel or PVC-U outside. Cite BS EN 13658-1 or -2 for metal beads, state how they are fixed, and check the reaction to fire of PVC-U beads on external walls.
Beads are the cheapest items in a plastering package and the ones that decide whether the finished walls look crisp. They set the line of every corner and edge, and the depth of the plaster against them. Most clauses simply say "beads as necessary", which leaves the plasterer to choose the bead, its depth and its material. The result is usually galvanised beads in external render that rust through within a few winters, or stop beads butted across a structural joint that cracks straight along the line.
This guide covers Uniclass Pr_35_90_07_63 Plaster beads, for beads in wet plaster. Neighbouring codes cover the related products: Pr_35_90_07_72 Render beads and Pr_35_90_07_73 Render stops for external render, Pr_35_90_07_88 Thin-coat plaster beads for skim over plasterboard, and Pr_35_90_07_24 Dry lining beads for taped and jointed board.
What does a plaster bead clause need to cover?
Some properties are specific to plaster beads. Others belong in every product clause. A clause that leaves either out gives the contractor room to substitute.
Properties of plaster beads
- Nominal sizeLength and wing width to suit the background.
- FixingsPlaster dabs internally; mechanical fixing for external render.
- Finish depthMatched to the total plaster or render thickness.
- FinishPlain metal, or coloured where the bead nose stays visible.
- Material gradeCoated steel or stainless grade, or PVC-U formulation.
- Corrosion protectionGalvanising is for interiors and sheltered positions only.
- Reaction to fire classificationNever guessPVC-U beads are combustible; check external walls.
- Product typeWhich bead at which edge, corner or joint.
What every product clause needs
- Manufacturer and product referenceNamed bead range and reference for each bead type.
- Product standardBS EN 13658-1 inside, BS EN 13658-2 outside, for metal beads.
- Installation methodFixing, mitring and cleaning as the M20 general clauses.
- Technical submittalsData sheets for each bead; BBA certificate for PVC-U.
- Operation and maintenance informationBead references for patch repairs later.
- MaterialGalvanised steel, stainless steel or PVC-U.
- ProfileAngle, stop, movement, bellcast or feature section.
Uniclass Pr_35_90_07_63 Plaster beads. Not every property applies to every project; where one does not, say so rather than leaving it blank.
Fields marked Never guess (reaction to fire classification) depend on the project and should never be filled from a default or a previous job. If the information is not available yet, the clause should say so with a TBC and a reason.
Which decisions does the clause depend on?
Most properties follow from the product you choose. These depend on the project, so they need a decision from the designer before the clause is written.
- 01
Which bead goes where
Bead typesEach edge condition has its own bead. Angle beads form and protect external corners. Stop beads finish plaster cleanly at openings, abutments with other materials and changes of background. Feature or architrave beads give a shadow gap at door linings and window boards instead of a timber architrave. Movement beads form a control joint in the plaster. Outside, a bellcast bead at the bottom of render throws water off the face. A real M20 specification lists each condition separately in the beads clause, and that is the easiest way to make sure none is missed.
How to decide
- List the conditions on the project: external corners, abutments, openings, base of render, control joints.
- Assign one bead type to each, with a manufacturer reference or a description.
- Decide whether openings get feature beads or timber architraves, and keep it consistent with the joinery schedule.
- Show any exceptions on the drawings rather than relying on "as necessary".
Write it asExternal corners: angle bead. At abutments with other materials: stop bead. Around door linings: engaging feature bead. Base of render: bellcast bead. - 02
Bead depth and plaster thickness
DepthA bead is a screed guide as well as an edge. Its depth sets the finished thickness of the plaster against it. A bead that is too shallow leaves the plasterer feathering out to nothing at every corner; one that is too deep leaves thick plaster at the edges and thin plaster mid-wall, or a bead nose standing proud. Two-coat plaster on masonry, skim on plasterboard and three-coat external render each need a different bead depth, so the bead line in the clause should refer to the thickness in the plastering or rendering type clause, not to a size picked from a catalogue.
How to decide
- Two-coat plaster on masonry: a standard plaster bead to suit the specified total thickness.
- Skim on plasterboard: thin-coat beads, which are a different product code.
- External render: render beads to suit the render system thickness, including any mesh layer.
- Where backgrounds are uneven, allow for dubbing out so the bead can still be set true.
Write it asDepth: To suit total plaster thickness in clause 200. Thin-coat beads to plasterboard skim, as clause 280. - 03
Galvanised, stainless or PVC-U
MaterialGalvanised steel beads are standard inside. Outside, galvanised steel rusts and stains through render, and manufacturers restrict even galvanised beads with a PVC nose to sheltered or moderate exposure. Stainless steel or PVC-U are the normal choices for external render, and in harsh coastal or industrial environments some manufacturers recommend PVC-U because stainless can still corrode. The bead also has to suit the plaster: at least one manufacturer advises that its stainless beads are for cement-based renders and should not be used with gypsum plasters unless supplied with a protective finish.
How to decide
- Internal gypsum plaster: galvanised steel beads.
- External render, normal exposure: stainless steel or PVC-U render beads.
- Coastal or aggressive environments: check the manufacturer's guidance; PVC-U may be preferred.
- Wet internal areas behind tiling: follow the plaster and bead manufacturers' joint recommendation.
Write it asMaterial: Internally, galvanised steel to BS EN 13658-1. Externally, stainless steel to BS EN 13658-2. - 04
Movement beads and structural joints
MovementMovement beads allow a small amount of movement in the plaster face and are meant for control joints at changes of background or in long runs. They are not designed to cross structural movement joints, and manufacturers say so. Where a structural or expansion joint runs through the wall, the plaster or render has to stop either side of it with a pair of stop beads and a sealant joint between them, as real M20 specifications do in a separate sealant movement joint clause. Junctions between dissimilar backgrounds that do not need a joint get crack control mesh instead.
How to decide
- Structural and expansion joints: two stop beads with a sealant joint between, centred over the joint.
- Control joints in long runs or at changes of background: movement beads, at positions shown on drawings.
- Junctions of dissimilar solid backgrounds with no joint: crack control mesh as the M20 clause.
- Mark every joint position on the elevations and internal elevations.
Write it asMovement joints: At structural joints, stop beads either side with sealant joint as clause 653. Movement beads only at control joints shown on drawings. - 05
Reaction to fire of PVC-U beads
Never guessSteel beads are non-combustible and rarely raise a fire question. PVC-U beads are combustible. BBA certificates for PVC-U render beads state that they are not non-combustible and that the regulation on materials in external walls restricts their use in some cases. Where regulation 7(2) applies to a building, every material that becomes part of the external wall needs to be class A2-s1,d0 or A1 unless it falls within an exemption, so the choice between stainless steel and PVC-U beads has to be confirmed with the fire engineer and building control rather than left to the plasterer.
How to decide
- Relevant buildings under regulation 7(2): specify stainless steel beads unless the fire engineer and building control accept PVC-U in writing.
- Other external walls: check the Approved Document B route the fire strategy uses before accepting PVC-U.
- Internal linings: metal beads raise no lining class issue; check PVC-U beads against the lining class where the fire strategy is strict.
Write it asReaction to fire: External render beads in stainless steel, non-combustible. PVC-U beads not permitted on this building without fire engineer's written acceptance.
The values under "Write it as" are examples. The right value depends on the location, the use and the fire strategy.
Which standards should the clause cite?
Cite the product standard the declaration of performance refers to, the code of practice for installation, and the test method behind each value you set. A value without its test method cannot be checked against a submittal.
- BS EN 13658-1
- Metal lath and beads. Definitions, requirements and test methods. Internal plastering
Definitions and requirements for metal beads and lath used in internal plastering.
In the clause "Beads: galvanised steel to BS EN 13658-1."
- BS EN 13658-2
- Metal lath and beads. Definitions, requirements and test methods. External rendering
The same for metal beads and lath used in external rendering, where corrosion resistance matters most.
In the clause "Render beads: stainless steel to BS EN 13658-2."
- BS EN 13914-2
- Design, preparation and application of external rendering and internal plastering. Internal plastering
The design and workmanship code for internal plastering, including the use of beads at corners, edges and joints.
In the clause "Plastering, including beads and stops: to BS EN 13914-2."
- BS EN 13914-1
- Design, preparation and application of external rendering and internal plastering. External rendering
The design and workmanship code for external rendering, including render beads, bellcast beads and movement joints.
In the clause "Rendering, including beads and movement joints: to BS EN 13914-1."
- BS EN 13501-1
- Fire classification of construction products and building elements. Classification using data from reaction to fire tests
The Euroclass system used to check whether a bead material meets the class required for external walls.
In the clause "Render beads on external walls: Class A2-s1,d0 or A1 to BS EN 13501-1, or non-combustible steel."
- BS EN 15651-1
- Sealants for non-structural use in joints in buildings and pedestrian walkways. Sealants for facade elements
Facade sealants, used in the joint between pairs of stop beads at structural movement joints in render.
In the clause "Sealant between stop beads: to BS EN 15651-1, colour to match render."
Confirm the current edition of each standard at every issue. Avoice's State of UK Specifications 2026 found a withdrawn standard cited in 40% of specifications at contract issue.
For the regulations behind these choices, see Approved Document B explained, or search the Avoice Regulations library.
How do you write it in CAWS?
In CAWS, beads are written in M20 as their own clauses, not as a line in every plastering type clause. Real M20 specifications have one clause for beads and stops internally and another for beads and stops externally, each listing the condition and the bead for it, then a beads and stops generally clause for fixing and finishing. The plastering and rendering type clauses in the 100s and 200s simply say "beads, stops as clause 634".
Sealant joints at structural movement joints, with stop beads either side, usually have their own clause too, and crack control at junctions of dissimilar backgrounds sits in a further clause. Dry lining beads for taped and jointed plasterboard are written in K10, not here.
- Manufacturer
- Submit proposals
- Product reference
- Submit proposals for each bead below
- Product standard
- BS EN 13658-1
- Material
- Galvanised steel
- External corners
- Angle bead
- At abutments with other materials
- Stop bead
- Around door linings and window boards
- TBC Interior designer still choosing between engaging feature bead and timber architrave. Resolve before ordering.
- Control joints
- Movement bead, at positions shown on internal elevations
- Depth
- To suit total plaster thickness in clause 200
- Plasterboard skim
- Thin-coat beads, as clause 280
- Fixing
- Plaster dabs or mechanical fixing to manufacturer's recommendations, true to line and level
- Corners
- Neat mitres at return angles
- Reaction to fire
- Steel, non-combustible
- Finishing
- Surplus plaster removed from bead noses while wet
Illustrative, not from a real project. One property is left as a TBC with a reason so it can be tracked and closed before issue.
Clauses the type clause relies on
- M20/640
- Beads/ stops generally Locations, mitres, fixing in longest lengths plumb and true, mechanical fixing outside, cleaning off.
- M20/646
- Crack control at junctions between dissimilar solid substrates Mesh across junctions that do not need a movement joint.
- M20/653
- Sealant movement joints with stop bead edgings externally Stop beads centred over the substrate joint, sealant between.
- M20/710
- Application generally Plaster applied to the beads, with the finished surface flush with the bead nose.
- M20/715
- Flatness/ surface regularity Permitted deviation, which the bead line has to achieve at corners.
Clause numbers vary between NBS versions and practice masters. The numbers here follow a real NBS M20 tender specification; what matters is that the type clauses refer to bead clauses that exist in your M20.
How do you write it in Uniclass?
In Uniclass the bead is a component of the plaster system. Ss_32_46_65_55 Multicoat plaster systems describes the background, coats, thickness and finish, and lists the beads by condition, pointing to their product clauses.
Each bead material is then a product clause under Pr_35_90_07_63 Plaster beads, holding the range, standard, material and depth. External render beads are better written under Pr_35_90_07_72 Render beads and called up from the render system, so the stainless steel requirement stays with the render.
- Description
- Two-coat gypsum plaster to internal blockwork walls
- Background
- Dense concrete blockwork
- Coats
- Gypsum undercoat and finish coat, as plaster product clauses
- External corners
- Pr_35_90_07_63 Plaster beads (B01), angle beads
- Abutments and edges
- Pr_35_90_07_63 Plaster beads (B01), stop beads
- Control joints
- Movement beads at positions shown on internal elevations
- Flatness
- As BS EN 13914-2 for the specified finish
- Execution
- To BS EN 13914-2
- Manufacturer
- Submit proposals
- Product reference
- Submit proposals for each bead type
- Product standard
- BS EN 13658-1
- Material
- Galvanised steel
- Types
- Angle, stop and movement beads
- Feature beads at openings
- TBC Interior designer still choosing between engaging feature bead and timber architrave. Resolve before ordering.
- Depth
- To suit total plaster thickness in the plaster system clause
- Length
- Longest available lengths to minimise joints
- Reaction to fire
- Steel, non-combustible
Illustrative. Performance of the finished system sits in the system clause; properties of the product sit in the product clause.
In NBS Chorus the Uniclass product clause for plaster beads also carries the NBS reference 45-75-05/340. Use whichever your practice's masters use, but do not mix CAWS and Uniclass references in one specification.
What goes in the spec, and what goes in the schedule?
The specification defines each type once. The schedule and drawings say where each type goes.
In the specification
What the product is and how it performs and is installed. Written once per type.
In the schedule or drawings
Where each type goes and how much of it. Changes with every plan revision.
The bead clause says which bead goes on which condition; the drawings say where the conditions are. Mark movement and structural joint positions on the elevations, because a bead clause cannot locate them.
What are the common mistakes?
Most problems are a missing property, a property filled with the wrong kind of value, or a decision left silently open.
- "Beads as necessary". The plasterer chooses type, depth and material. List the bead for each condition.
- Galvanised beads in external render. They corrode and stain the render. Specify stainless steel or PVC-U.
- Movement bead across a structural joint. It cannot take the movement and the render cracks along it. Use stop beads with a sealant joint.
- Plaster beads under a skim coat. Standard beads are too deep for skim on plasterboard. Use thin-coat beads.
- PVC-U beads on a relevant building. They are combustible. Confirm the bead material against regulation 7(2) first.
- Joint positions left to site. Control joints end up where convenient, not where the background moves. Draw them.
How Avoice helps
Avoice's spec writer drafts bead clauses from your plastering and rendering information, and shows what it could not settle.
- Drafts from your drawings and schedules
It reads the plaster and render types from the finishes schedule and elevations, picks the M20 bead clauses or the Uniclass system and product headings, and lists the bead for each condition your information shows.
- Leaves a TBC with a reason
If the treatment at door openings has not been decided, or the building height means the render bead material needs fire engineer sign-off, the line says TBC and why. Every TBC joins one project register to close before tender.
- Writes in your format and style
Choose CAWS or Uniclass. Avoice adapts your practice's own M20 masters rather than replacing them with generic text.
- Checks the clause against everything else
QA/QC flags a render clause that calls up clause 635 when only 634 exists, galvanised beads in an external render type, or a movement joint shown on the elevations with no bead or sealant clause.
- Keeps product data in one place
Bead data sheets and BBA certificates sit in the Product Room, linked to the clause, so a substitute can be checked against the material and depth asked for.
Related guides: How to specify lime plaster, How to specify sand and cement render, How to specify plasterboard.
Software can draft and check. The designer still chooses the product and is responsible for the specification.
Draft your plaster bead clause in Avoice
Upload your drawings and schedules. Avoice drafts the clause in CAWS or Uniclass, cites the standards and flags anything your information does not settle.
This guide is for general education and is not professional advice. Check current editions of standards and Approved Documents, the manufacturer's data, and the requirements of your project before relying on any clause.