Table of Contents
Rendering your house is a way of making it waterproof by enclosing the structural components such as brick, stone or concrete block (or even mud!) with a shell made from mixing cement, sand and lime with water. There are quite a few different types of render which can mostly be differentiated by the texture of the surface and how they are applied.
What is the difference between plaster & render?
You will probably have heard of these terms and know approximately what they mean. But did you know that plastering and rendering are basically the same processes? Although both rendering and plastering are designed to provide a smooth surface on which you can decorate, one is exterior and one is interior. Because exterior wall rendering is exposed to the wet weather it needs a different proportion of its ingredients to make it weatherproof. Interior plastering is not exposed to the weather so its primary purpose is to produce a smooth and hard surface. The following table shows the relative proportions of ingredients in plaster and render and will probably give more of an idea as to why they are different. (Figures are given by the Civil Engineering Portal.)
|Parts By Volume|
|Top finish coat||1||12||30|
|Top finish coat||1||3||6|
As you can see, proportionally, render has more cement in its mix, and plaster has more lime and sand. Render also uses coarse sand while plaster uses fine sand so that a plaster finish is smoother.
To summarise the similarities and differences between plaster and render:
- They both serve as a covering for walls to give a smooth and hard protective surface.
- Rendering protects an outside wall while plastering protects an inside wall.
- The exterior render mix contains more cement because the purpose of the covering is to provide a weatherproof and secure shell.
- The interior plaster mix contains less cement because it doesn’t have to be weatherproof.
- A render mix for external walls uses coarser sand than an internal plaster mix.
How Much Does Rendering Cost?
Sand and cement are relatively cheap commodities compared to other construction materials, so the largest proportion of the cost to render a house comes from labour charges and scaffolding.
Full scaffolding will always be necessary when working on a house of more than one storey because to produce a professional and weatherproof render coat, it is essential to apply the render without stretching the body unnecessarily. To successfully apply render the professional needs to exert a continual and strong pressure to ensure the render bonds together. There is no way that this can happen if the professional is working on tip-toes, from a single scaffold tower or a ladder.
Typical house rendering prices will always vary depending on a number of factors.
- Ease of access.
- Rendering cannot be done in severe rain (rain will wash the cement out of the mix) or in temperatures below 4 degrees centigrade (the water will form ice crystals and expand, interfering with the chemical reaction between cement and sand).
- Rendering cannot be done in the full heat of the sun because the water in the mix will evaporate before it has a chance to complete the chemical reaction.
- Size of house.
- Whether any preparation work or repairs have to be done before the render coat is applied.
- Whether the top coat is smooth or textured.
- Which part of the country you are in. London and the South East will always be more expensive than elsewhere.
|House size||Price range||Duration|
|2 bedroom bungalow||£2,500 to £3,500||4 to 6 days|
|3 bedroom semi-detached house||£4,200 to £5,500||6 to 9 days|
|4 bedroom detached house||$6,700 to £8,300||7 to 14 days|
A bungalow does not need full scaffolding for access to the walls. However, depending on his or her physique, the professional may need to have a platform made from scaffold boards resting on two or three concrete blocks placed at intervals along the boards. All buildings with more than one storey will need scaffolding to provide a safe working platform. In the table above, scaffolding costs are not included for the bungalow but are included for the houses.
An important point that needs consideration is that if there is any existing render, it will have been waterproofed either by a coat of exterior grade paint or by some other means. The waterproofing substance will prevent the correct bonding between the new and existing render so all the existing render must be removed. The prices given are therefore for:
- Removal of existing render.
- Repoint and key existing brickwork.
- Application of new render.
- Smooth sponge finish to new render.
Prices do not include the application of exterior paint and any other exterior render textured finish.
Other textured finishes
Smoothcast or smooth sponge finished render (so-called because a wet sponge is drawn across the surface to provide its characteristic texture) has its advantages but can be boring to look at. You may find that planning constraints restrict your choice of textured finish on any external render. What rendered finish is allowed may depend on the traditional finish of the buildings in your locality or whether your building is subject to a conservation order.
Another common finish to give some interesting texture is known as pebble dash render. The surface is produced by throwing gravel onto the wet render topcoat using a shovel. Once all the surface has been covered, the pebbles will be gently pressed to ensure a good bond between the gravel and the render. Pebbledashing might sound simple but it requires the gravel to be thrown with a consistent force against the wall. It also requires the base render to be at precisely the correct stage in its chemical reaction and drying process. If the render is too wet the gravel will knock the render from the wall. If the render is set too much then the gravel will not stick. Having said this, pebble dashing was very popular during the late 1940s and 1950s as the construction industry suffered from a skills shortage and pebbledash was a way to disguise low-quality rendering.
Roughcast is another textured finish that is similar to pebbledash. Rather than using gravel, roughcasting a wall is done by throwing a pre-mixed mixture of mortar and stone chippings onto a smooth top coat of render.
Both pebbledash and roughcast are useful ways of :
- Providing very low maintenance decorative finishes.
- Disguising poor quality rendering.
- Providing a hardwearing surface.
- Improving ability to shed rainwater.
- Giving high impact resistance.
When pebbledash and roughcast surfaces are painted, the operation is very labour intensive. The uneven surface requires more care to ensure every part has been covered.
If you want a textured finish on a smoothcast or sponge finished surface but don’t want the extra expense of pebbledash, some exterior paints are available with a textured finish. These exterior paints are able to fill cracks in the surface and will soak into the render to provide a very good waterproof protection. Remember that all types of paint will wear off because of weather action so this will require regular maintenance and repainting. One way around this is to mix a mortar dye and a waterproofer in with the final top coat mix. This will give a colour of your choice that will not be affected by weathering and doesn’t need painting. You must take care to add the dye consistently in all the render mixes so that the wall is the same colour throughout.
Another method of giving a textured finish is to apply a Tyrolean finish (or Weber render) to the render. This is also known as an Alpine finish and is an ornamental render that originated in the Austrian Alps. This needs the standard base and top coats of render on the wall as usual. On top of this is placed the Tyrolean finish. It can be bought in a variety of colours and is mixed separately in a bucket. The cementitious render finish is preblended with its colouring so that the only necessity is to add water and apply. It is applied by means of a Tyrolean gun. This is a machine with a reservoir to hold the mix. The operator turns a handle which rotates a metal comb that flicks tiny lumps of finish onto the wall.
- The Tyrolean mix is pre-blended and only needs the addition of water on site.
- It is a durable covering and very weather resistant.
- The colouring is consistent throughout the mix and doesn’t require any subsequent painting.
- It can be applied indoors and out.
- It provides a sound absorbing finish to internal render.
Typical prices of Weber Cullamix Tyrolean render are about £45 per 25kg bag. Depending on the thickness of the Tyrolean coat, this bag will cover approximately 0.5m2.
Who will do the work?
As a general rule, there are two tradesmen who will be able to apply render to an outside wall.
- A plasterer.
- A bricklayer.
Both these trades will understand how to go about preparing and applying render in all its forms.
If you want to have a go at rendering a wall it won’t be easy. Not only must you ensure that full adhesion takes place, but you must also ensure the thickness of the layer remains the same all the way across the wall; make sure the surface is as smooth as possible; and remove any holes or cracks where water can get behind the render and lift it off when it freezes. A professional learns how to use the tools of his trade and how best to mix and properly apply the sand and cement during a long and structured training programme such as an apprenticeship. Don’t expect to learn to apply sand and cement render from watching a few YouTube videos, it just isn’t going to happen. Something like a rendered wall that is vital in keeping the inside of the house free from damp is not something to play around with. There are however small jobs that you can attempt yourself. Start with a small patch where the existing render has crumbled away. There are often plenty of those around a door or window frame, so start small and learn how to fix blemishes and repair cracks in the surface before you try anything more adventurous.
If you wish to find a professional who can apply render to your house, look locally for a plastering or building company that has many years of trading history in your area. Not only will you avoid the ‘fly-by-night’ cowboys that infest the construction industry but you will also have the benefit of contacting people who the company has worked for previously. You can inspect the rendering done in previous years and see how it stands up against the weather. Don’t forget to ask friends and family about bricklayers or plasterers that they might have used before.
Having the outside walls of your home covered with a mix of sand and cement render is a good way to waterproof the building if the existing brickwork is starting to crumble with age, and render looks good too. Choose the tradesman wisely and remember that both bricklayers and plasterers know how to apply render. If you choose a local company to do the work for you, they will often know if there are any planning constraints in your area that will restrict your rendering options.
Before your professional starts work, make sure you know exactly what you want. It isn’t any good changing your mind halfway through from wanting a sponge finish to a pebbledash finish.
Finally, when your new rendered walls have been completed, remember to look after them and maintain them according to the style you have chosen. You can then look forward to many years of trouble free service.