Rendering walls is one of the UK’s most popular forms of finishing external walls – and for a good reason. Here’s how to get it right.
There’s a lot to be said for rendering walls. It’s part of our building heritage, it creates a subtle, uniform finish; it doesn’t require an additional foundation for support; done well, it keeps the rain out; and, in most comparisons, it’s highly cost-effective compared to its competitors brick, stone and timber cladding. Add in the fact that it can be coloured in any way imaginable, and you’ve got a flexible, stylish wall finish.
Poorly done, or in the wrong place, however, and it can be a high-maintenance problem you can’t avoid. It can lose that fresh look within months with cracks, bubbles and mould all appearing and making that cost-saving look like a poor investment. So it’s essential to approach a rendering project with care and consideration of the issues.
How much will render cost?
You should allow £30 – £60/m2 (of facing wall) for a rendered wall (which includes painting). So a typical three-bedroom semi-detached home with around 90m2 of walling might cost in the region of £2,700 – £5,400. The job might typically take up to two weeks, and you should allow £500 – £800 for scaffolding costs.
A smaller bungalow, which has less wall area and will require less scaffolding, will cost £1,500 – £3,000.
Using a monocouche render will be more expensive, but there are long term savings on maintenance to be enjoyed. Typical costs (including labour) are in the region of £50 – £80/m2.
What is render?
One way to think of render is similar to internal plasterwork, where a mix of sand and cement (and occasionally lime) are mixed together, applied, and then dry off on the wall. It can be installed to provide a smooth finish, or mixed with aggregates to a rougher, (commonly known as roughcast or pebbledash) coat. It usually consists of two applied layers and then painted – although modern render solutions are single-coated, through-coloured and mixed with silicone.
Expert exterior wall rendering demonstrated by Ross Ashton of City Damp Solutions in Hampshire.
Render – planning permission & building regulations
Render is more common in some parts of the UK than others, but outside conservation areas and other specially-designated planning areas (such as Areas of Outstanding Natural Beauty), it’s usually considered a good option for people building houses from scratch. Existing homeowners looking to replace the whole existing external finish (e.g. brick) with render will find they can carry out this project under their permitted development rights – meaning it does not require planning approval.
Rendering at least 50% of any wall, or over 25% of the walls of the whole house, will make your rendering project subject to building regulations – in particular, the need to improve the thermal efficiency of the wall itself, through additional insulation (see below).
When should I avoid render?
Rendering doesn’t suit all houses, and it doesn’t suit all locations. Clearly, a home with a smooth render finish in a row of similar dwellings would look reasonably unusual – as would a house with a particular character such as a barn conversion.
One of the essential techniques to ensuring a good quality long lasting render is to ensure the render has the ability to dry out after getting wet – which means a combination of access to sunlight and movement of air. So render on part of an elevation (particularly the lower part) that is north facing (getting only very minimal early morning and late evening sun if at all), heavily shaded (by neighbours or trees) and very close to fencing or other buildings is going to struggle to survive many years without suffering from mould or algae. There are ways around this unhappy occurrence, but you need to pay particular attention to the application and maintenance.
Be careful, too, when you apply the render. Experienced renderers will not apply render in the colder months for fear of the water in the mix freezing and effectively blowing the whole coat off as the ice expands and contracts. Equally, rain is best avoided as it can literally wash newly applied render off walls and certainly affect your mix. Most renderers can handle hot weather, but warm sunny weather can make a poorly mixed render dry out too quickly before it has had a chance to take to the wall.
“Before” and “After” examples of professional rendering, showing the transformation of the exterior appearance. All project work credited to City Damp Solutions in Hampshire.
How is render applied?
- Every renderer has their own favourite mix – some use lime, others don’t – and most tend to slightly vary the mix between coats. A good starting point is a 1:2:2 mix of cement, building sand and sharp sand.
- Ensure the wall is damp but not soaking wet. Apply the render firmly but in a relatively thin coat, so that it is around half a centimetre thick. The point is that this first coat needs to suck into the wall. Too thin and it will be ineffective as a base – too thick, and it will fall off.
- Scratch the coat to open it up a bit before it dries – this is known as providing a key.
- Apply the second (final) coat, which should be twice the thickness of the first. While it’s still wet, run a level bit of timber over the render to get it even and smooth.
- With the render drying out but not totally dry (ideally within a couple of hours at the maximum), firmly move a float over the render. This is designed to close up any holes in the surface and provide a smooth finish. You can then go over the wall once more with a damp sponge to give that perfect finish.
- The render is then painted.
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What happens when render goes bad?
A poor application can lead to all sorts of problems down the line. The most common issue is cracking, which is where hairline cracks in the surface begin to be invaded by rain which, in the winter freezes and expands, making the crack bigger. The root cause of this is something we can’t do much about – houses tend to move with the seasons and create pressure on a fixed surface like render (which is why lime adds a touch of much-needed flexibility). However, the topcoat of render needs to be properly floated with a sponge to ensure it is properly closed to water ingress.
Occasionally render will bubble – often caused by the topcoat being applied too soon after the first has had the chance to go off.
Mould (black) and algae growth (green) occur on darker parts of the wall, typically nearer the ground, where breezes and sun struggle to dry out a damp render (render, of course, gets wet all the time, and dries out thanks to the wind, sun and heat). Ironically, the better insulation the wall has, the less heat passing through the render and the less chance it has to dry out, too. Additionally, rough and pebbledash surfaces pick up grime by their nature. An excellent quality fungicidal wash should remove it, and conventional coatings prevent it recurring.
Pros of render
- Relatively cheap (mainly traditional render) compared to other finishing options
- Huge variety of colours
- Quick to apply
Cons of render
- Can result in high maintenance levels to maintain the appearance
- Doesn’t suit all situations
- Success is heavily dependent on the skill of the installer
Because of the many potential problems with render as outlined above, several new approaches to rendering have emerged. The most exciting is monocouche render which, as the name implies, is a pre-mixed render that requires just one coat to apply – saving installation costs – and, more importantly, includes both silicone and pigmentation in the mix (with a variety of colour options) – which means that the render coat is both flexible and through-coloured. This saves your painting costs but more critically ensures that the render will not crack or require painting in the years to come.
Monocouche render – lookout for experience with manufacturer’s names such as K-Rend in your preferred renderer’s profile – has a higher upfront cost than traditional sand and cement render but is increasingly the preferred route as it cancels out so many of render’s potential disadvantages and maintenance.
Rendering and Insulation
Re-rendering your home is an excellent opportunity to consider the energy performance of the exterior walls. Indeed, you may well have to: if you intend to replace or install render on 25% of your entire walls or 50% or more of any wall, building regulations stipulate that must ensure that the wall insulation meets current requirements.
If your home is one of the 20m households in the UK with a cavity wall, then you’ll be able to fill the cavity with an injected insulation. Note that fully-filled cavities are not always recommended in specific locations. Many energy companies offer free cavity wall insulation installation as part of their ROC programmes. If you have a single skin wall, you could use the rendering process to add boards to the outside of the house, which most experts agree is the better option compared to internal insulation as it moves the dewpoint outside the home’s envelope. This process is known as EWI (External Wall Insulation) and combines well with a render finish. It’s expensive and means altering the window reveals (meaning more prominent sills) and alterations to the junction with the roof.
How long will render last?
A well-installed traditional sand and cement render can last a few decades before it needs replacing, although it will need maintenance on a five-yearly cycle to ensure it looks as good as can be. In the meantime, cracks and bubbles will need to be repaired.
Modern monocouche renders are designed to last at least 30 years, although in theory should last much longer.
The Rendering Process Explained
- First of all, decide whether your rendering project needs planning or building regulations approval.
- Decide on which type of render you would like to use and the preferred colour.
- Engage with three local renderers you’ve found on Checkatrade.
- Get quotes for the project, along with suggested dates for the work. Ideally, the tradesperson will be able to give you guidance on the best colour and render type. Agree whether you or the renderer is responsible for scaffolding and/or materials.
- As with any significant building work on your house, it is worth informing your home insurance company, particularly if the house did not have a render finish before.
- Rendering commences and should take 2-3 weeks for a standard detached home, and 1-2 weeks for semi-detached or bungalow. A single house wall should be rendered within 3-5 days.
What about patch repair costs?
If there is a small amount of cracking on the render, it can be repaired using one of the pre-mixed render repair tubs available from the merchants. This can usually be done on a DIY basis, but if you want to hire a renderer to do the job, it will likely cost in the region of £100 – £200 for a small patch. Be aware that it is only ever likely to be a temporary repair and the finish will need to be of equal smoothness to the rest of the render to blend in well.
How can I save money on render?
While it’s best to leave the rendering to an experienced and skilled tradesperson. Smooth, long-lasting finishes are not easily achieved by beginners, You can save money by offering to paint a traditionally-rendered wall yourself. Again, it’s not for the faint-hearted but can be handled on a DIY basis. It costs around £400 – £600 for a week’s scaffold hire, depending on the size of the house, If your renderer has already hired out the scaffolding, it makes sense to get them to do it on the same hire. An additional week on a scaffold hire is much cheaper than a standalone week.
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