Specifying the right beading for external rendering - Renderplas
Specifying the right beading for external rendering - Renderplas
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Specifying the right beading for the external rendering of residential housing and commercial buildings
- What is rendering and why is beading important?
- What are the various beading types on the market?
- Meeting the required standards
- Key criteria to look for when specifying beading solutions
- What makes beading made from recycled PVC the right choice?
Developments in rendering have, over the past 30 years, led to finishes widely recognised as distinctive and durable. They have provided opportunities for architects looking for innovative alternatives to cladding across a wide array of buildings. The importance of selecting the right rendering materials has grown alongside these ambitions.
Rendering beads are extruded components that are punched with holes to provide a strong key to fix the render material to the surface wall when it reaches ends, joints and corners. They create structurally sound well-defined edges, support bold aesthetic choices and prevent render damage.
Although their function seems relatively straightforward, it should not be assumed all rendering beads are the same. It is important to identify which options best suit the project specification, desired environmental and sustainability performance and overall safety objectives.
2. What is rendering and why is beading important?
Rendering is the process of applying a wet mixture, traditionally cement, water and an aggregate, to property walls to achieve the desired finish once dried. Today, acrylic polymers and silicone have joined minerals as base material options. These provide better waterproofing, cleanliness and resistance to algae and moulds. They also present the opportunity to add coloured pigments. Exposing aggregates within a render can create attractive effects. Scraping and trowelling can also add different textures to the choices available to architects.
Impactful use of rendering has become a feature of recent housing developments, major public buildings and commercial properties. Examples include sports stadia (London 2012 Aquatics Centre), luxury hotels (Wynn Palace Resort, Macau), cultural venues (The Victoria and Albert Museum, London) and high-profile residential developments (Chelsea Harbour Village, London).
Fixed to background walls, lengths of rendering beads provide necessary support for end, corner and joint reveals within any render material. Without beading, finished surfaces are not only unsightly but at significant risk of damage. While there are various beading variants available, the vast majority fall into four well-established categories.
• Corner beads, also known as angle beads
• Bellcast beads, also known as drip beads
• Expansion joints, also known as movement joints
• Stop beads
Stop beads mark points where the façade changes, including breaks for windows, doors and other building features. They provide a straight finish and protection against impact damage.
Corner beads finish corners and reveal a sharp, well-defined look and feel, as well as protecting them from impact damage and wear.
Bellcast beads finish the base of render material just above the damp proof course and reveals. They provide a straight edge, provide protection from impact damage and throw off water to prevent ingress. They owe their name to a slightly thicker render, said to resemble a bell in shape, which can also create a shadowing architectural effect.
Expansion joints allow for any thermal expansion or compression anticipated in the render material or structural movement in the background wall. Typically installed at regular (5m) intervals in any render, they are also often used between coloured or textured render panelling and provide a gentle shadowing effect.
Additional beading is available for more specialist applications such as interior dry lining, external wall insulation (EWI) systems and external thermal insulation composite systems (ETICS).
All beads provide additional protection to render at its most vulnerable points. They prevent impact and wear-and-tear damage from passing people and objects, spalling through freeze-thaw action and cracks caused by any structural movement.
Preparing the surface wall is a key initial task for any rendering contractor. Beading is then cut to length on site and fixed to the surface wall before the render application. Methods vary depending on the type of surface. Most beads need to be plumbed straight and set level onto blockwork with render for example. Adhesive mortar can be used if stronger bonds are required. Large profile wide-wing beads can be flexible enough to level out background blockwork themselves. In this case, non-corrosive mechanical fixings, such as nail clouts and hammer-in plugs may also be used. Mechanical fixings are best suited to timber frames and insulation systems providing they have been correctly levelled off.
The process of cutting to length depends on the material but a hacksaw or tin snips normally suffice. Where beading meets, compound mitres give the best finish, however, wings can be overlapped. Beads are normally rigid enough to be installed by a sole construction worker.
3. What are the various beading types on the market?
The market is dominated by beads made of stainless steel and PVC. Only steel and PVC are acceptable materials under current British Standards (BS EN 13914:2016). Zinc coated steel solutions, where galvanised steel has been hot dipped in zinc after fabrication, is a cost-effective alternative to stainless steel but not widely used in the UK. Due to the risk of corrosion, it is not recommended for damp, humid or salt-laden environments. Non-coated galvanised steel beads are often used to cut costs but present a significant corrosion risk whatever the environment. For this reason, they fall outside British Standards and their use is generally discouraged.
Polyvinyl Chloride (PVC) is a synthetic thermoplastic now widely used in the construction industry for windows and doors, fascias, weatherboarding, piping and cabling. PVC beading was introduced to the UK in 1990. Its cost is in line with zinc-coated galvanised steel beading, at roughly a third of the cost of stainless steel, but with zero risk of corrosion. PVC also resists impact well by absorbing shockwaves and will not permanently deform or bend. Pigments can be introduced to match the PVC beads to the colour of the render for a more professional and aesthetically pleasing finish. This is not possible with steel beading where the beads’ arris will be visible after scraping. This might make for a desirable architectural feature in some cases. If not, beads require painting to achieve the desired finish.
The depth of render also needs to be considered. Steel beading is designed in standard sizes with the arris maintained at the right level by bending the bead wings as required. This can leave air gaps and opportunities for moisture to build. PVC beads are made to match specific render depths and their wings lie flush against the rendered surface.
As well as functionality, most building components are now assessed against a range of sustainability targets. Beading is no exception. Steel and PVC, in their raw states, have comparable environmental impact. This can easily be illustrated by the amount of carbon dioxide (CO2) released during their production. A figure of 2.3kg of CO2 per kg of finished steel was identified in a study for CSIRO minerals by the University of New South Wales and Commonwealth Scientific and Industrial Research Organisation. Figures for raw PVC reach 2.1kg according to a similar study from the European Climate Foundation. Processing can add significantly to greenhouse gas release. The CSIRO study found that the figure for stainless steel can reach 6.8kg of CO2 per kg of finished product depending on how it is made.
Rendering beads from recycled steel and PVC are widely available too. PVC can be readily recycled at the manufacturer’s premises. This can be done at a relatively low temperature of 180°C. Using recycled PVC in beading has been shown to deliver energy savings of over 80% (Ecopoint). Steel, in comparison, needs to be melted at around 1370°C, which is a significantly higher temperature than PVC. As a result, the process for steel requires significantly more infrastructure and transportation. Comparative figures for recycling stainless steel suggest only a 33% saving over new product (Yale University). PVC also supports energy conservation once installed by avoiding cold bridging effects associated with metal components.
The two beading options, steel and PVC, share a function yet have clear differences across a range of properties and characteristics. A working knowledge of these differences will lead to better specification and procurement decisions.
4. Meeting the required standards
The latest British Standard applicable to external rendering was published in March 2016. BS EN 13914:2016 covers the design, preparation and application of external rendering and internal plastering. It prescribes the appropriate tools, techniques, materials and equipment to use when undertaking projects. Experienced render contractors and plasterers will recognise the guidance as general best practice. The publication acts as a thorough introductory guide to external rendering procedures for others.
BS EN 13914:2016 addresses the selection of beading for external rendering and stipulates stainless steel and PVC as acceptable materials. Hot-dipped galvanised steel is also permitted with caveats related to the levels of salt in the environment and associated corrosion risks. Corrosion risk is also cited as the reason uncoated galvanised steel beading is not permissible as a material.
Failure to comply with BS EN 13914:2016 when selecting steel beading could have serious commercial and contractual implications should external rendering suffer from rust related discolouring, cracking, or adhesion failure at any point. PVC beading comes with no corrosion risk.
Alongside British Standards, those purchasing beads should also assess them against a range of other quality, operational, safety and environmental criteria.
5. Key criteria to look for when specifying beading solutions
In assessing the suitability of beading for any rendering project, the whole supply cycle from initial design considerations to onsite delivery and installation ought to be considered. For example, the selection of beading can have a significant impact on overall rendering costs. Bead unit costs vary by up to 300% depending on the material. Typical wastage rates through cutting to size need to be considered alongside any damage rates during transit and storage. Handling and cutting beading materials varies in practicality. Care must be taken to avoid bending steel beading out of form. It can also be challenging to cut on site without leaving a sharp edge.
Minimising the risk of injury during the handling and cutting of beading is a key consideration during installation. Long-term building safety, including fire protection, is also a key consideration. Products can vary significantly in safety performance and certification.
Components such as rendering beads also have a role to play in a building’s overall sustainability performance. As we have seen, levels of recycling and energy consumption involved in their manufacture vary significantly. Performance can be checked, prior to purchase, against a range of measures and certification schemes such as the British Board of Agrément (BBA) certification and BRE Green Guides.
Alongside practical considerations, it is worth remembering beading has a key role to play in fulfilling the architect’s aesthetic requirements. It may need to be matched to coloured render for example. Any visible arris may need to be reduced in size or painted. The likelihood of rusting, discolouring and cracking over time should also be assessed.
6. What makes beading made from recycled PVC the right choice?
PVC has been used to make rendering beads in the UK for 30 years. In this time, it has gained a proven track record of success. Light and robust, it reduces wastage by resisting damage and malformation during transit and installation. It does not form a sharp edge when cut to size with small hacksaws or tin snips. This makes PVC beading a valuable improvement to onsite safety, which is more important than ever. It is also ideal for use in plastering and rendering training too.
PVC beads are available in a range of colours giving architects the freedom to make vibrant choices, with no need to repaint. They will also not discolour or stain during drying or through water damage over time ensuring their aesthetics remain for the life of the building. PVC beads also absorb impact well and offer superior protection to edges and corners and they do not readily support combustion. Reputable beading solutions are certified as self-extinguishing upon the removal of a flame (BS 467 Class 1Y) and do not introduce additional hazards or contribute to the combustion of a system.
Raw PVC does not normally present a danger to human health by inhalation, ingestion or contact with the skin and therefore, PVC beading has been certified as compliant within Registration, Evaluation, Authorisation and restriction of Chemicals (REACH) controls.
PVC beads also impact positively on energy conservation. They require less energy to manufacture than stainless steel beading from both virgin and recycled source material. They also remove ‘cold bridging’ weak spots in building insulation associated with metal components supporting compliance with Part L of English Building Regulations and the general schemes of the Building Regulations of Wales, Scotland and Northern Ireland.
PVC beads have also been designed to outlast metal equivalents. Examples have been guaranteed for the lifetime of the render and at least 25 years. At the end of their design life, the PVC can then be fully reclaimed and recycled up to 40 times.
100% recycled steel is not available. PVC beads made from 100% recycled material present the specifier with a level of sustainability that cannot be achieved by any other material permitted in the British and European standards. PVC beading is roughly a third of the cost of stainless-steel beading too. This, and other benefits over alternatives, explains the recent growth in its use across a broad range of housing, commercial and public buildings.
Beading specification impacts on every phase of a rendering project including initial cost, ease of installation, quality of finish, corrosion protection, energy conservation and long-term durability. There are clear benefits to undertaking product research and challenging the assumption all beading is the same. Leaving specification to the rendering contractor late into a project risks beading being selected because it is the cheapest or most easily available. It may not support the overall building goals as well as it could.
Does the chosen beading, for example, meet the architect’s requirement for render colour and texture? What impact will it have on a building’s sustainability targets? How long will it last? What are the corrosion risks? These questions, and more, ought to be considered at a project’s design phase. As rendering grows in sophistication and ambition, answers seem to increasingly lead towards PVC, preferably recycled PVC, becoming the beading material of choice. It is likely to be seen in many more commercial properties, homes and public buildings in the future.
8. Renderplas – Our solutions
Renderplas introduced PVC beading to the UK in 1990 and have, since then, been the country’s leading supplier to housing and commercial builders. They are also the only major supplier to commit to energy conservation and the removal of virgin PVC from their supply chain. Renderplas white beading is made from 100% recycled materials and across the whole range of colour variations produced, the recycled material content is 90-95% which is the highest level of recycled material available on the market.
The company also takes great pride in designing and delivering robust, plasterer-friendly products that offer a wide range of benefits to architects, contractors and end-users. Renderplas holds up to one million metres of stock across its expansive range at any given time. The range includes bellcast beads, corner beads, expansion joints, stop beads and dry lining beads. The company also supplies specialist render meshes, beads and fixings for External Wall Insulation (EWI) systems and External Thermal Insulation Composite Systems (ETICS). All are available direct from Renderplas through UK next day delivery or via a range of global stockists.
Renderplas offer a wide range of profiles for straight durable joints, sharp lines and clean corners for render and plaster depths between 4mm and 22mm. Nine colours are available from terracotta to sky blue. Each option and has been carefully selected to colour-match render from leading suppliers including K Rend, Parex, Ecorend and Weber.
All Renderplas PVC beading is manufactured in the UK and conforms to BS EN 13914:2016, the standard for external rendering. It has been awarded an ‘Excellent’ rating by BRE’s Green Guide, complies with COSSH and REACH legislation and is approved by the BBA. This includes fire safety as per BS 476-4:1970 and BS EN 13501-1:2007. Renderplas products are guaranteed for the life of the render or at least 25 years. The beads that make it into your project have the highest possible quality and sustainability credentials when they come from Renderplas.
All orders are supported by a friendly and dedicated team of knowledgeable Renderplas staff. They can provide architects and contractors with product design information and CAD drawings as well as technical advice and customer service. This all benefits from a range of practical project experience including the following examples.
Projects using Renderplas solutions
Historic Seafront Renovation
Due to the wet and salty environment, Renderplas’s PVC beading was the only product that could ensure no rust or unsightly bleed-through would occur during the renovation of a Grade 2 listed Victorian property on Brighton’s seafront.
Harsh Environment Luxury Resort
Renderplas exterior beading supported the dynamic design for the Kingdom of Bahrain’s first high-end open-air mall complex, which included shops, restaurants and an art gallery. PVC beads were selected, rather than steel, due to the harsh environment. Their edges were designed to be visible as an enhancement to the building’s striking aesthetic.
Modern Weather Resistant Timber Framed Housing
Renderplas bellcast beads have been used to weather-proof oak timber framed houses by a leading specialist UK builder. PVC beads proved easier to fix to timber frames than metal alternatives. They have the flexibility to match the frame contours while offering high weather resistance. Renderplas also supplied beading in a range of colours that matched project and planning requirements.
Stylish Country House Hotel and Conference Centre
Renderplas recycled external beading provided a durable cost-effective solution for a 37 room two-storey hotel extension project in Aberdeenshire. Renderplas beading, used with a spray applied silicone-based render, helped provide a low maintenance, high-quality water-resistant finish that complemented the main building’s architectural style. Renderplas beads meant no additional painting was required despite the use of through-colour render. This, together with ease of installation, cutting and fixing, helped the contractor achieve a tight schedule.