Render keeps rain off a wall and can hide poor brickwork underneath, but the type matters more than the colour. A silicone render sheds water and needs little upkeep, which suits most modern cavity-wall houses well. Put the same coat on an old solid wall and it can hold in moisture that used to escape through the face, turning a smart finish into a damp problem behind the plaster.
Render systems compared: sand and cement, monocouche, silicone and lime
Traditional sand-and-cement render goes on in two or three coats, built up over several days to a thickness a plasterer judges by eye and experience. Pebbledash render is a variant of this: the same sand-and-cement base coat, but with small stones thrown onto it while still wet, common on British houses from the early twentieth century. Monocouche render is a factory-mixed, through-coloured product applied as a single system, usually in two passes despite the name, and it needs no painting afterwards because the colour runs through the material. Silicone-based renders are a type of thin-coat, one coat render with added resins that make the surface water-repellent while still letting some vapour escape, which is what has made them popular on modern houses. Lime render works differently again: it hardens slowly by absorbing carbon dioxide from the air rather than curing like cement, and the result is soft, breathable and flexible enough to move with an old wall instead of cracking.
Which render suits which wall: why breathability matters
An old solid-brick or stone wall, broadly one built before around 1920, has no cavity to stop rain: it copes by letting damp that soaks into the face evaporate again, with the lime mortar in the joints doing much of that work. Wrap a wall like that in a render that is largely waterproof, and moisture can get trapped inside instead of on the surface, with nowhere to go but further into the brick, where frost and salts do the damage over a few winters. SPAB’s guidance on lime and cement renders spells out how it happens with hard cement render: a coat more rigid than the wall behind it forms hairline cracks, and those cracks draw in rain that then cannot dry out. A house built from around the 1920s onwards usually has a cavity wall, and the cavity does the job of keeping the inner leaf dry, so a water-repellent render on the outer leaf carries much less risk, the same logic by which a mortar mix has to suit the brick it is laid with.
Silicone render is a system, not a tub of paste
A silicone or monocouche render is sold as a system, not a single product: a primer or bonding coat, the render itself, a reinforcing mesh where the substrate needs it, and sometimes a top seal, all specified by one manufacturer to work together. Weber, Parex, K Rend, Sto and Baumit are among the manufacturers active in the UK, and each publishes technical data sheets and only guarantees its own complete system. Mixing a base coat from one maker with a top coat from another voids that guarantee, and plasterers who cut corners this way are a common cause of render failing years before it should. Drying and curing times vary by product and by weather: a silicone render can cure within a week or two in mild, dry conditions and take substantially longer in a cold, damp autumn. Whoever quotes should be able to name the system, supply its data sheet and put the guarantee in writing; silicone render is not one interchangeable product.
What a render job costs, and what drives the price
Preparation is usually the biggest variable in a render job, not the render itself. Hacking off old, failed render, raking out and repairing cracked or soft brickwork underneath, and boxing in pipes and cables can take as long as applying the new coat, and a wall in poor condition adds substantially to the price. Across the main trade cost guides, a straightforward monocouche or silicone render on sound cavity walls comes to roughly £45 to £90 per square metre, labour and materials included, with prices highest in and around London. Lime render tends to cost more, both because the material is more specialist and because it takes longer to apply and cure properly, and a specialist finish such as brick slips or render over external insulation costs more again. With a band that wide, the useful comparison is line by line: the preparation, the render system and the drying time each quote allows.
Cracks in render, and how to clean it safely
A hairline crack in render is most often cosmetic and worth watching rather than acting on straight away. A crack that keeps widening, runs in a straight diagonal line, or lets water track down the wall behind it is a different matter, and the render is rarely the real cause: differential settlement, thermal movement or a fault in the coat underneath is the likelier culprit, so it is worth a builder’s or surveyor’s opinion rather than a quick sealant fix. Colour plays a part too: a dark render on a south-facing wall heats and cools more than a pale one, and that wider swing in temperature opens hairline cracks a lighter colour would not show. Cleaning carries its own risk. High-pressure jet washing can strip the surface of render and old mortar alike, especially anything already soft or previously painted, and once that surface layer is gone the render weathers faster underneath. A soft wash or a gentle hose is safer on anything older than a few years, with a small test patch first.
When a change of render needs permission
Re-rendering a wall in a similar colour and finish to what was there before is usually treated as maintenance and needs no permission. That changes if the property is listed, where consent is generally needed for work affecting its character, including render over previously bare brick or a marked change of colour, or if it sits in a conservation area under an Article 4 direction, which can withdraw the normal right to render, clad or paint a wall without asking first. Building Regulations sit alongside planning, not in place of it: renovating render over a large enough share of a single wall’s surface can trigger a requirement to bring its insulation up to a current standard, even where the wall itself was never going to be touched. Routine patch repairs sit outside all of this. A change of colour or type, or re-rendering more than a small area, is a question for the local planning authority before the scaffold goes up, because undoing it costs far more than asking.
