RENDER BOARDS

Render board is a solid and durable external construction panel with backing surface designed for thin polymer coat render systems such as K-rend, made to withstand the extreme weathering effects of wind, rain and snow. In fact, render boards create better substrate than blockwork or brickwork and are mostly used on treated timber and steel frame buildings. Render carrier boards are popular due to high bending strength of 17N/mm2, however, thick coat renders such as ‘sand and cement’ are not compatible with external render boards. Sand & Cement Render is a heavyweight (more than 45kg per m2) top coat finish which can easily weaken the construction and therefore should not be used with render carrier boards. Thin coat render carrier boards start from thicknesses 6mm, 9mm, 12mm up to 20mm and can withstand a thin coat plaster of up to 2mm. Regardless of the brand, it is strongly recommended using a 12mm thick render carrier board to ensure extra strength and stability. When a project has a render board specified, it should be a board that has the capability to be directly rendered to and hold a third-party accreditation (namely a BBA certification) for the intended application or meet the harmonised standard BS EN12467:2012. Render boards, being impact-resistant, dimensionally stable and weatherproof are specifically formulated to achieve a strong key between basecoats and top coat K-rend renders. Boards are also easy to work with as they can be cut onsite. These features make them a popular rendering solution. You will typically find that the render carrier boards on the UK market come in two popular thicknesses of 9mm and 12mm. Only Siniat Bluclad board comes as a 10mm board. Render boards are typically supplied as ivory and grey boards in 4’x 8’ panels with coverage of 2.88m2. Product can last for many years without losing effectiveness and is more than capable of resisting potential hazards such as mould and time-induced wear. It has a thermal conductivity of 0.12W/mk which makes this product a high insulator throughout the year.

RENDER BOARD APPLICATIONS

Render board is suitable for receiving a wide range of finishes including various render types, paint, thin coat plaster and brick slips, making it the ideal choice for both internal and external applications such as fascias or bargeboard. It is also ideal for use as part of an exterior wall cladding render systems, timber frames, leisure buildings, park home board, stud partitioning, flooring, ceilings and dry lining. Sheets are designed to be used as a render carrier board, where there is no insulation applied to the board prior to rendering. It is recommended to isolate the board from the inside.

RENDER BOARDS MANUFACTURERS | PRODUCTS

Different render carrier board manufacturers create boards with different properties, however render carrier boards are often characterised by high tensile strength which resists bending to prevent cracking and deformity. Boards are made by many leading manufacturers such as Knauf, Siniat, Fermacell, RCM, Cembrit, STS, Econic or Magply. Some boards are lighter and easier to cut when others don't offer 'score and snap' cutting technique. However, most of them offer class A1 (non-combustibility). The most common Render Boards on the UK market are Renderflex, Aquapanels, STS and Siniat boards. Render boards are widely available, you can buy them easily in stores such as Wickes or Jewsons.

The  boards are available in a range of sizes to suit your individual requirements. This render board range includes the following readily available product thicknesses: 
6mm ǀ 9mm ǀ 10mm ǀ 12mm ǀ 12.5mm ǀ 15mm ǀ 20mm
Other thicknesses can be supplied on request. 

All boards are easily applicable measuring 2400mm x 1200mm, 2400mm x 900mm, 2600mm x 1200mm and 1200mm x 900mm.

PRODUCTS

• Knauf Aquapanel
• Siniat Bluclad
• Fermacell PowerPanel H2O
• RCM Multipurpose
• RCM Renderflex Render Carrier Board
• RCM Y-Wall 
• RCM SILTECH
• Magply Render Carrier Board
• STS Render Carrier Board
• Cembrit Permabase Render Board

RENDER BOARDS PRICES

Because render boards can be used in so many different situations, it is important to know you’re getting the best price, particularly if you’re working within a tight budget. If you are looking for the render-boarding cost per m2 – you would be looking for £26.40 per m2 (as of 2022 - based on 12mm render board). Full sheet board would cost you £76.04 (2.88m2). On the top of that you will be hit with render boards accessories costs such as Knauf Aquapanel Exterior Stainless Steel Screws/SN40 – £35.42, Knauf Reinforcing Mesh – £198.40, Knauf AQUAPANEL Board Primer – £67.15, Knauf AQUAPANEL Joint Filler and Skim Coating –  £71.42, Knauf AQUAPANEL Tape – £38.12.

RENDER BOARDS BUILDING REGULATIONS

According to current building regulations render onto board backgrounds shall be suitable for the intended use and detailed to provide satisfactory performance. Issues to be taken into account include:

1. Provision of a system manual

Where render is applied to a board background, the render manufacturer should clearly define the system in a manual, including:

• materials and components,
• common details,
• design guidance,
• installation guidance.

The system should be used in full accordance with the manufacturer’s guidance and recommendations.

2. Compatibility between the render and background

The background should be appropriate for its intended use. Issues to be taken into account include:

• compatibility between the board and render, 
• durability classification of the board and its suitability for use in exterior conditions, including resistance to weather prior to the render being applied.

Render onto board backgrounds should:

• not be applied where the surface has contamination, dust or loose particles,
• consider the effects of solar radiation (colour, orientation and shading),
• be mixed to ensure colour consistency where coloured pigments are specified,
• be specified and used with the appropriate ancillary items, such as trims to form corners and returns.

3. Fixing back to the structure

Board backgrounds should be fixed back to the structure in accordance with the manufacturer’s recommendations.

The fixing design should consider:

• wind load,
• pull-out strength,
• pull-through resistance,
• anticipated movement.

Fixing battens and rails should be installed vertically and not block drainage paths. Timber battens should be suitably treated. To reduce the risk of damage from impact, especially at low level, where people have access around balconies and where cradle systems etc. can come into contact with the façade, appropriate precautions such as closer supports should be considered. Cavity barriers should be appropriately detailed to ensure satisfactory performance and:

• be provided in accordance with building regulations,
• not block ventilation or drainage paths,
• account for movement in the frame,
• be used in accordance with the manufacturer’s recommendations.

4. Weather resistance

Timber and steel framed backing walls should have a minimum 25mm cavity. Cavities to timber framed walls should be drained and vented, and cavities to steel framed walls should be drained.

5. Movement joints

Movement joints should be provided to accommodate movement in timber frame structures. Where board backgrounds are used, movement joints should be:

• formed in accordance with the system manufacturer’s recommendations,
• continued through the background board,
• positioned to accommodate calculated deflection or movement provided at floor zones.

6. Board backgrounds

Board backgrounds to be rendered should be external grade and recommended for use in the render manufacturer’s system manual. Boards should be set out in accordance with the system manufacturer’s recommendations, taking account of possible compression, deflection and alignment of joints in relation to openings in the external wall, such as windows and doors. The render should have alkali-resistant mesh embedded into the base coat across the whole surface. Edges of boards should be suitably treated to provide protection from weather during construction and to maintain durability after the render is completed.

RENDER BOARDS INSTALLATION PROCEDURE

Render boards can be drilled, screwed and nailed with conventional hand tools. When specifying a render board, the customer must always ensure they have conducted their own checks to ensure the specified board meets their performance requirements and that the correct fixing and installation works are completed in accordance with board supplier’s recommendations. All render carrier boards should be attached to either wooden battens or a steel frame in a staggered formation. Each board should also have a 3 – 5mm gap between them and their neighbouring board. Ensure that you use stainless steel screws because the rust will come through to the render over time if standard screws are used. Ensure the head of the screw fixing is flush with the board surface. Crooked screws that are not flush must be removed and replaced.
Using a basecoat, fill the 3mm joints between the boards, then apply render mesh over the joints and lightly trowel the mesh onto the adhesive basecoat surface. Once all the joints have been filled and meshed, apply a further adhesive basecoat to the entire surface with a minimum thickness of 3 mm. Lightly trowel render mesh to the surface of the 3mm coat. The individual render mesh lengths must be laid horizontally and must have a minimum overlap of 100mm. Once the entire area has been meshed add a further adhesive coat over the top of the entire meshed area troweling to a smooth finish.
Once the meshed basecoat has dried minimum 24h you can apply a primer to the surface of the meshed basecoat and allow it to touch dry before applying textured acrylic or silicone renders. All joints should be then protected with carrier board joint tape. All render boards require conventional mesh to be placed over the whole surface area of the boards. The mesh is generally pressed into the base layer of render however different render suppliers will have their own application instructions which must be followed. Render boards can be cut, drilled and worked with joinery machinery or a jig saw.

WHAT SIDE DO I RENDER ONTO?

All render carrier boards are dual faced. The smooth, unprinted site is for rendering applications. The textured side is on the reverse. 
We recommend that the 'smooth face' is rendered onto (smooth side out). If the boards have been installed rough side out, make a note of the batch number against the project name and render can be applied to the rough side. The batch number is on the rough side.

DO I NEED PLANNING PERMISSION TO ADD EXTERIOR FINISHES?

Changes to your home’s exterior appearance may be subject to planning rules set down by your local Council – so always check with them first. Your budget, the look of other houses nearby, or what your local Council approves will all influence the material you choose for your exterior.

WHAT IS THE DIFFERENCE BETWEEN CEMENT PARTICLE BOARDS AND RENDER CARRIER BOARDS?

While render carrier boards are not affected by weather and moisture, cement particle boards as a non-specialist boards, have elements within their composition that are highly susceptible to water penetration, retain moisture and swell which drastically affects their capability. Pull-off and pull through values will be wholly affected and all non-suitable boards will cause the render system to fail. A wood-based board, cement particle board or a non-approved board should not be used externally where render application is required.
Apart from initial construction difficulties, moisture retention under the right conditions provides the medium for mould to form and spread behind the render system. Cement patrice boards may also become unstable and if mould growth is apparent, could create health implications to the building occupants too.

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Video credit:https:https://www.youtube.com/watch?v=dGC_0xqHplU