Render is a coating of mortar or proprietary material applied to the external face of a masonry wall to provide weather protection, improve appearance, and cover a substrate that is either unattractive or too porous to be left exposed. Traditional sand-and-cement render is applied in two or three coats. Modern proprietary systems include monocouche (one-coat) render applied in a single thick coat, silicone-modified render (highly flexible and water-repellent), and acrylic thin-coat systems applied over an insulated external wall insulation (EWI) carrier board.

What is the difference between render and plaster?

Render is an external wall coating applied to the outside face of a building to provide weatherproofing. Plaster is an internal wall coating applied to the inside face to provide a smooth, paintable surface. Both are applied in similar ways and use similar materials - but render mixes are typically coarser and stronger to resist weather, while internal plaster is finer and lighter. In everyday speech, 'plastering' often refers to both, and internal browning coat (undercoat) plaster is sometimes called 'floating coat' or 'render' internally.

What is monocouche render?

Monocouche (meaning 'single coat' in French) render is a factory-blended through-coloured cement-lime-sand mix applied in a single coat of 12-20mm. The colour is integral rather than painted, so it does not peel or need repainting - the colour weathers gracefully. It is applied by machine or by hand, scratched with a devil float to texture it, and requires no finishing coat. Monocouche is popular for new-build housing and extensions where a coloured render finish is wanted without the maintenance of paint.

How long does external render last?

Well-applied traditional sand-and-cement render that is painted regularly can last 20-30 years. Monocouche render, being through-coloured, can last longer without repainting - 25-40 years. Silicone and acrylic thin-coat renders have a design life of 25-30 years. Render life depends heavily on substrate preparation, mix design, curing, and regular inspection and maintenance of any cracks - small cracks allow water ingress that causes the render to delaminate from behind.

Finishes noun / verb

Render

/ ˈrɛndə /

Also known as: external render, sand-and-cement render, monocouche, roughcast, pebbledash

Definition

Render is a coating of mortar or proprietary material applied to the external face of a masonry or timber-frame wall to provide weatherproofing, improve appearance, and protect the substrate. Traditional render is a two- or three-coat application of Portland cement and sand. Proprietary systems include single-coat monocouche render, flexible silicone render, and thin-coat acrylic finishes over external wall insulation boards.

In practice

Traditional sand-and-cement render uses a scratch coat (1:3 to 1:4 cement:sand, 10-12mm), keyed before setting, then a float coat (1:4 to 1:5, 8-10mm) to level the surface, and optionally a finishing coat (fine-textured, 3-5mm) or a paint finish. The mix must be weaker in each successive coat - a stronger outer coat over a weaker base will delaminate. Mesh reinforcement (alkaline-resistant fibreglass mesh) bedded in the scratch coat significantly reduces cracking on timber frame and at wall openings.

Monocouche render is applied in a single 15-20mm coat using a factory-mixed through-coloured material - no paint required. Silicone render incorporates silicone to increase flexibility and water repellency, reducing cracking and algae growth. For external wall insulation systems, a thin 5-8mm reinforced basecoat embeds the carrier mesh and a 1.5-3mm decorative topcoat provides the final finish. All rendered surfaces need movement joints at large-format panels and at all openings.

Building Regulations

Relevant PartPart C - Resistance to weather and ground moisture

Conservation areasRender colour and finish may require planning permission

Fire (EWI systems)Part B - Combustibility of render carrier boards above 18 m

Approved Document C requires external walls to resist weather. Render is one of the recognised methods of achieving weather resistance for masonry walls. On buildings above 18m in height, Approved Document B introduced restrictions on combustible materials in external wall systems following the Grenfell Tower fire, which affects EWI systems incorporating combustible insulation or carrier boards. In conservation areas, changes to render colour or finish may require planning permission.

Full Building Regulations guidance

Related Calculators

Render & Plaster Calculator

Render

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