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External Rendering specialists - what you need to know

There are few building services that create such an instant and striking impact on the look of your home as rendering. Even the most dated of facades can be revamped and modernised in a matter of days with a smart newly rendered finish.

While any home can be rendered, you (and your rendering professional) will need to consider a few factors before the new surface can be applied. First, take a look at the existing substrate – the material that your render will sit on top of. The main consideration here will be whether that substrate provides enough adhesion to render onto.

Next, have a think about the type of finish you’re looking for. Different types of render offer specific styles – some more traditional, some more contemporary. It’s usually sensible not to “force” a style on your home, by trying to make a more modern property look older, or vice versa.

And finally, speaking of the age of your home, that comes into play too. As well as steering the type of finish that’s most appropriate, it will also determine how much preparation and ongoing upkeep may be required, and how much substrate movement your new rendered surface will need to handle.

Cost of external rendering

Rendering jobs are typically priced according to the surface area that needs to be covered. But the type of render you opt for will also affect the overall price.

• Standard sand and cement rendering should cost anywhere from £30–£50 per sqm.
• K Rend (a more resilient and smoother render) and other silicone or acrylic renders are pricier, with costs ranging from £45–£75 per sqm.

How to render an external wall

Trusted, reliable rendering experts know that there’s no shortcut to the perfect finish. So, they’ll usually follow this five-step process:

1. Scaffolding – your tradesperson will need a base to work from, so they’ll begin by putting up scaffolding with a few levels, so they can access all areas of each wall to be rendered. They should then protect your windows by covering them with plastic sheeting.
2. Remove old render – the next step (which will only be necessary if you’re covering an existing rendered surface) is to get rid of any old render. Your tradesperson will usually do this with a dedicated vibrating tool.
3. Keying – to provide maximum grip and adhesion, your pro will then key the existing surface. Keying simply involves making grooves in the substrate.
4. First render layer – your renderer can then apply the first coat. This layer is referred to as the “scratch layer” because it’s scratched to give a rough surface that provides adhesion. The scratch layer consists of a 4-to-1 sand and cement mix, and is usually around 7–8mm deep.
5. Final render layer – once dry, the second topcoat render layer can then be applied. Like the first layer, it will be around 7-mm thick but this time your pro will probably use a 5-1 sand and cement mixture. This final layer will be screeded and wiped a few times to help ensure a smooth finish.

Types of external wall render

• Sand and cement render. The most common and cost-effective option. Made using Portland Cement, it’s also a strong, resilient render. However, because it’s so tough, sand and cement render is prone to cracking when applied to substrates which move or flex. For that reason, cement renders usually aren’t recommended for older buildings. Cement renders aren’t waterproof either, so they usually need a waterproof masonry paint applied to protect against moisture penetration.
• Lime render. This render has two main advantages over cement – it’s both breathable and very flexible. That makes it well suited to older homes, which can suffer from substrate movement. Lime render isn’t waterproof, but it can provide an effective moisture barrier as it absorbs water and stops it from passing through the wall. And, because lime render is breathable, the moisture then gradually evaporates.
• K Rend and polymer renders. You might have read about or heard the name K Rend mentioned when researching render options. K Rend is the product name of one of the leading modern render finishes. Like competitor products, K Rend is essentially a cement-based mix which incorporates specially engineered polymers to improve the durability and finish. In the case of K Rend, silicone water repellents help to block out moisture while retaining breathability. That means the surface keeps its freshly rendered appearance for longer, and is more resistant to algae growth and lime bloom (a natural discolouring). As well as silicone-based options like K Rend, alternative nylon and glass fibre options deliver stronger coats while ensuring breathability.

The qualifications your external rendering expert needs

Rendering is essentially another form of plastering. City & Guilds qualifications, apprenticeships and diplomas in plastering and rendering are useful in showing your tradesperson has invested in their skills, but formal qualifications are not required to become a plasterer.  

The most important consideration when seeking out a rendering professional is experience and evidence of completing similar jobs to a high standard previously.

Insurance for external rendering

While renderers won’t need to enter your home, that doesn’t mean things can’t go awry. With scaffolding going up, and your windows, vehicles and garden furniture all at risk (not to mention the tradesperson’s own safety), it’s crucial that your pro holds full public liability insurance. Ask for a copy of their cover before your tradesperson begins work.

Questions you should ask your external rendering expert

• What type of render would they recommend using, and why?
• Is K Rend an option for your home? If so, how much extra will it cost?
• Will they organise scaffolding for you, or do you need to arrange this?
• Will they paint the render (if necessary), or is this down to you?
• What ongoing maintenance will your rendered surface require?