Cladding Options: Buying Render

ABOVE: The render on this self build was applied as 'through-coloured', but it can also be painted in any shade desired. Read more about this self-build...

Houses have been getting their walls daubed with something or other ever since they first had walls. The reasons are twofold.

Firstly, to protect the actual walling material from the effects of weathering and rainwater penetration, and secondly, to make the walls look good — i.e. as a decorative effect. But what material is best? And how should it be applied?

There is now a range of choices. The standard practice has been to use cement renders, but there is a re-emergence of interest in lime and clay plasters — materials not widely used for 60 years or more. And coming up on the outside is a new and big push for what we are learning to call ‘monocouche’ renders. Monocouche is French for ‘single layer’ or ‘bed’, and that is the key to understanding these renders. Conventionally, both lime and cement renders have been mixed on site with sand and applied in a series of layers or coats, never less than two and sometimes three or more. In contrast, a monocouche render is supplied in bag form ready for mixing with water: it can be applied by hand trowel or sprayed on. It’s a practice which has spread here from the Continent and many of the big names in this field – Sto, Knauf Marmorit, Weber – are German.

These renders use white cement and are pre-coloured (in any colour you want) so that what you are applying is as much a decorative finish as weatherproofing layer. As they can be applied in one coat – typically around 15mm thick – they are much less labour intensive than traditional renders.

The downside is the material cost — a 25kg bag costs between £8-10 and only covers a square metre of wall area. This compares with a materials cost on a traditional cement render of around £1/m². However, monocouche render systems claw much of this added cost back through reduced labour, not to mention eliminating the need for subsequent painting.

Monocouche renders also have additives which make them more flexible and help to eliminate cracking. They can even be ‘selfcleaning’ (rain clings to the dirt; try Sto).

What about lime? Green builders love lime and it has some advantages over cement renders, in that it is inherently more flexible than cement and you are less likely to have problems with moisture getting trapped within the wall — a problem when cement renders are applied to old walls.

Lime also tends to look very appealing, though it does require frequent coats of limewash. Building limes are available in a variety of formats, from traditional lime putties (which are bought wet, by the tub) through to a number of bagged products – hydraulic limes – which behave rather like a weak cement. They need to be mixed on site with sand, and are hand-trowelled in the traditional way. Limes are a little more expensive than standard cement renders, but shouldn’t really take any longer to apply.

There are even lime-based monocouche renders. Try K-Rend (K-Lime) and Baumit.

Further Reading:

• A Guide to External Appearances
• Cut Costs Not Quality
• External Renders