Paints & Renders Explained

External renders and paints give your home personality, while insulating and weatherproofing it
by Build It
26th November 2012

Change the external skin of your house, and you change its entire character. From a pebbledash terrace to a bright white Art Deco house, paints and renders can make a world of difference to your home’s aesthetics, with renders carrying the additional benefits of weatherproofing and insulation.

But bear in mind that while a (relatively) cheap-and-cheerful coat of paint on the exterior of your building is a quick way to give it a facelift, you may be missing out on some easy-maintenance, hi-tech products that can help to improve both breathability and durability.

Although render has been used as a building material for centuries, the neat, tailored look of smoothly rendered surfaces are now a particularly popular choice for contemporary homes. It’s also a common look for seaside homes or buildings in exposed places, because it brings an extra layer of protection from the elements. Mix rendered surfaces with other textures such as masonry or timber cladding, and you can add architectural interest to your build; Victorian terraced houses are often left bare brick at the front, but rendered at the rear.

For extensions, an all-over render can be a great way to unify your old and new space. If you’re a self-builder, you may not have a say in whether or not to use render – in certain areas of the country where it’s considered the vernacular style, such as in rural Scotland and much of Ireland, it’s practically a prerequisite to receiving planning permission. You may also be restricted in the type of render you can use, and its colour.

Coat of many colours

A coat of paint is the quickest way to change the character of any masonry building’s exterior. Painting bare brickwork is pretty much a no-going-back arrangement, however, so think hard about whether you’d be happy with your choice long-term, and check the paint is suitable for your type of brick.

Start with clean walls with no mould or plant life attached and then choose between a smooth or textured finish (textured finishes are especially good for covering minor cracks); most masonry paints will require a couple of coats, but there are one-coat products available.

Although flexible and vapour-permeable, these paints are unsuitable for historic buildings that have been built using lime mortar (typically those dating from before the 19th century). Opt instead for lime-based or breathable water-based products.

Rendered habitable

Thanks to the Romans, rendered buildings have existed in this country for centuries. In years gone by, a mixture of sand and lime was used to coat the outside of buildings, which was gradually replaced by sand and cement in the 20th century. Now, there is an amazing variety of styles to choose from, including smooth and textured finishes, a ‘dry dash’ (aka pebbledash) finish and a ‘wet dash’ (aka roughcast, where small pebbles and render are sprayed on together). Render can also be combined with external insulation to dramatically improve the thermal performance of your home.

The problem with concrete render – especially if used with a traditional lime-mortar masonry substrate – is that it is impermeable and can lead to damp and rot. It’s also inflexible, which in a new building that may need time to ‘settle’ can have damaging consequences.

New breeds of ready-mixed silicon-based render – flexible, breathable and virtually maintenance-free – are a vast improvement on concrete. “All the materials we use are synthetic, so they can deal with the movement,” says Terry. They can be specified in any colour and usually consist of a basecoat and a top-coat, which together are still much thinner and lighter than concrete and therefore less likely to affect the stability of your home. Silicon renders are also fully breathable, so are suitable for historic buildings, as long as listed building consent or local planners don’t specify ‘like-for-like’ lime render – if in doubt, check with planners that your product is correct.

Silicon’s disadvantage is that conditions have to be right for its application – it’s not good to apply it in damp and wet weather with a dropping thermometer, or on a scorching hot day (not that these are ideal for working with any sort of render).

DIY-ers beware: rendering, just like plastering, is highly skilled and not something to tackle on your own. Most manufacturers’ warranties (typically five to 10 years) will be invalid unless you use an approved contractor. Some renders are sprayed-on using specialist equipment, making doing it yourself impossible in any case.

Match your build system

With such variety on the market, you need to know what will work best with your type of build. For example, if you wanted to render an existing pebbledash building as well as a new-build extension, you’ll need a product that suits a one-size-fits-all approach. Different build systems – masonry, insulated concrete formwork and expanded polystyrene for example – all have their optimum products.

More timber-frame buildings are using cement board as a substrate, and as insulated render becomes more popular many manufacturers offer all-in-one systems so you don’t have to worry about whether your insulation will work with your basecoat and topcoat of render.

Ease of maintenance is another point in favour of silicon renders. There are no ‘pores’ for dust and dirt to sink into, so it stays on the surface and gets washed away, and because no moisture stays on the surface it’s less prone to algae growth (although most standard renders will include an algae inhibitor).

If the walls do need a clean, specialist cleaning products are available from individual manufacturers, but a jet-wash or a scrub with some water and washing-up liquid should be enough.

The natural alternative

There is still a place for traditional lime render, in new builds as well as historic houses. If you are very eco-aware you may be more comfortable with the idea of using a natural rather than a synthetic product. Lime render can be used on earth, straw-bale and wattle-and-daub walls as well as more well-known build systems such as masonry, and its ‘imperfect’ appearance is just right for rural, vernacular styles of architecture, for example.

Just like its hi-tech synthetic cousin, lime render requires a subtly different mix of ingredients to suit the substrate and climate, and it should be applied in favourable conditions, ie not when it’s too hot or too cold.

Main image: The Malcolmsons’ self-build is clad in crisp white render, contrasting grey timber and glass

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