There are many reasons people choose house rendering as a cladding option. Sometimes render might be the best option for houses with discoloured or unattractive brickwork, acting to cover them up with a fresh new coating.
Other times, house rendering is chosen as a whole-house option, perfect for sleek contemporary homes and more rustic renovation projects alike. Commonly render is also chosen as a partial covering, in combination with stone cladding, bricks and timber cladding.
Whatever your reasons for looking at house rendering as an option, it is important to know the different types of product out there and to be able to make an informed decision when it comes to the right one for your project.
House Rendering: What is it?
Render is used as a cladding option. It is applied to the exterior of a home, much like plaster is applied to the interior walls. There are two reasons for applying render:
- to protect the underlying walling material from the effects of weathering and rainwater penetration
- to provide an attractive appearance to the house
These days there is a wide range of house rendering products, from the more traditional lime renders, popular with renovators, to those that also provide insulation and a through-coloured.
House Rendering Options
This is the standard or traditional render used on external walls. Cement render is usually mixed on site before being applied in two or three coats. The base coats (or scratch coats) are scored when they are still wet to give a key for the next layer. The top coat is applied more thinly and given a shiny finish, ready for painting.
Cement render tends to be cheap in terms of materials, but a little more expensive on labour due to the numerous coats. It also has a tendency to crack if the underlying structure should move.
Cement renders require regular repainting if they are to continue to look good.
Polymer renders are usually sold pre-mixed in bags with either white cement or lime as a base.
They have polymers and other plastic-based products added to them to make the render less prone to cracking. They are available in a variety of colours and are often through-coloured, which does away with the need for painting.
Acrylic renders are most often applied as a thin finish coat to seal and enhance the appearance or the underlying coat. They also bring colour and texture. Fibres are added to prevent cracking and give a durable, lasting finish.
Silicone is also used, promising even longer life and the capacity to be self-cleaning — some claim that when it rains, the silicone will allow rainwater to wash away any dirt.
‘Monocouche’ (French for ‘single layer’ or ‘bed’ renders) are relative newcomers to the world of house rendering. These products originated in Europe before spreading here, so many of the big names – Sto, Knauf Marmorit and Weber – are German.
Monocouche render is supplied in bags, ready for mixing with water. It can be applied by hand trowel or sprayed on.
Monocouche renders use white cement and are pre-coloured (in any colour you want). They can be applied in one coat (typically around 15mm thick), so are quicker and therefore less labour intensive than traditional house rendering products.
The main disadvantage of monocouche is the material cost. A 25kg bag costs between £8-£10 and only covers a m² of wall area. As a comparison, traditional cement render costs around around £1/m².
It is important to note though that monocouche render systems will save you on labour costs and maintenance — there is no need for re-painting.
Monocouche renders have additives which make them more flexible and help to eliminate cracking. They can even be ‘self cleaning’.
Although lime plastering fell from favour for some years, having been the traditional method for house rendering in this country, there has been a re-emergence of interest recently.
Although lime-based plaster tends to be a little harder to apply than regular Portland cement – meaning it is more commonly used in renovation projects and for conservation work – both Baumit and K Rend now supply polymer-enhanced lime renders which aim to overcome any related difficulties.
Lime plaster is a great option for those looking for a breathable house rendering system.
The advantages of lime render in include:
- It is more flexible than cement
- It is breathable so prevents problems with moisture getting trapped within the wall — a common problem where cement renders are applied to old walls.
- It looks very attractive and enhances the exterior of period homes in particular — though it does require regular coating with lime wash.
Lime house rendering products come in many different formats, including:
- Traditional lime putties (bought wet, by the tub)
- Bagged 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.
- Monocouche lime renders — try K-Rend (K-Lime) and Baumit
Lime render is a little more expensive than standard cement renders, but don’t usually take any longer to apply and are a must for many period properties if problems with damp are to be avoided.
Can I Mix Render with Cladding?
If you plan on using a combination of cladding materials on your house – great for visual appeal and to avoid a look that is too clinical on contemporary homes – there are a few factors to consider”
- The junction between two different cladding types give rise to potential waterproofing and airtightness problems
- It increases costs due to the requirement for separate suppliers and trades — it is also important to schedule each trade so they don’t overlap
- You need to consider the difference between those cladding which are self-supporting (brick and stone, for example) and those which need to be attached to something, such as render
Incorporating Insulation with Render
In the UK, much of the insulation upgrading has been done via the cavity wall, but cavity construction is uncommon in other countries. There the preference has been to add insulation to the outside of the existing walls and then render over the insulation.
In cases where there is no cavity wall insulation (and no way of adding it in this way, in houses with solid walls, for example) it is useful to consider external wall insulation (EWI) systems.
These are made up of insulation layers, meshes and top coat renders.
External wall insulation promises a modern, clean-looking finish and is a great idea for those worried about adding insulation internally to solid walls due reducing internal spaces.
While these new house rendering systems are more expensive than traditional cement renders, they can often be applied in one coat — greatly reducing labour costs. They can also be applied directly to blockwork or some other substrate and this has proved popular with those seeking a clean, contemporary finish.