Generally speaking the only time that most people have to get involved with the external finish of their home is when they are conducting some form of repair or maintenance. While this is a very important job and a sound understanding of the finish that you are dealing with will help, we believe that there is more to external finishes.
Due to the size of the average house any external alterations will inevitably involve quite a bit of work, but it is now possible to alter the look of your home dramatically with your choice of external finish, without it being the monumental job it used to be. We encourage people to do this if they have grown tired of the outside of their home.
Having said this, it is important to ensure that you are not going to contravene any restrictions placed on properties that are listed or in conservation areas and councils do have powers to revoke your right to finish your home’s exterior if it has received enough complaints. See below for exterior finishes that don’t work!
Factors Affecting your Choices for Exterior Homes Finishes and Renders
There are a number of factors that will affect your options when it comes to choosing your exterior finish. If you are aware of these you will be able to make a more suitable choice, but ultimately it comes down to your taste and how your choice will work in the setting that your home is in. Some of the most important factors include:
- Existing Substrate – This is the material that will be under the finish of your choice. This is particularly important when using a render as the render will have to adhere to this surface and move with it
- Age of the property – Not only will this affect the ascetical setting, the substrate and the method of construction, it will also have a bearing on the amount of preparation, repair and ongoing maintenance that you will likely have to do to the exterior of your home
- Your desired colour and finish effect – Unless you are in a listed property, this is the factor that should carry the most weight. You must ensure that your property is finished in a way that you find attractive and is in keeping with it’s environment. You don’t want to fall out with the neighbours
Homes are typically rendered because it is not possible to achieve a suitably attractive and weatherproof finish with the stone or brick work. Renders are also used when the exterior wall has been damaged and this is the cheapest way to make it weatherproof again. In some cases it is possible to rectify and recover brick and stone work, so that is looks authentic and attractive, there are several products on the market at current.
Broadly speaking there are three main types of exterior finish that you can apply to your home, and you may use one of more on a single property. These are the main types on finish:
Within these categories of exterior finish, there are numerous options available and we will cover these main options next – cladding will be covered in a separate project.
Finishing a Home with Render
Within the category of rendered finishes to a home, there are two distinct options; Traditional Renders and Special or Modern Finishes. They are much as they sound; the traditional renders are those that have been used on houses for a long time, some for hundreds of years with very little change, and the more modern ones are those that have been invented using new materials, techniques and technologies.
The term Stucco is often used to describe render, particularly in North America. This can be applied to all forms of render from lime renders and cement to more modern types of render all of which we discuss here.
Stucco, thought to be of Germanic origin, was widely and most popularly used in Italy where mortars and renders were lime based, reinforced with horse hair and applied in several coats forming the bases of what is now known as Venetian plastering.
The word Stucco has, over the years, been applied to almost every form of render but it is fair to say that originally it referred to the lime based pastes that were used, either in a smooth finish or a textured coat, to provide an attractive finished surface on an otherwise plain wall.
The key difference between the plaster that you can use on the interior of your home and the plaster or render that is used in the exterior is that the exterior render must be weather proof – It has to provide protection from the elements, particularly driving rain and it should be able to withstand temperature changes and fluctuation of moisture levels that an interior plaster does not need to.
The Components of Renders
Renders are made up of a variety of components, and the varying amounts will determine the type of render and its properties and characteristics. The name of the render will reflect the proportions of these constituent parts. The components of a render are:
- Binding Agent: This is the compound that acts as the adhesive and holds the render together providing its strength, moisture resistance and permeability. Typically it is cement, lime, clay or gypsum
- Structural Filler: This is the ‘volume’ that makes up the bulk of the plaster. Sand is the most common, but other aggregates are often used also
- Water: Water is use to work the render and typically activates the binding agent
- Fibre: These can be added to the render to provide strength and ‘stretch’, or tensile reinforcement and improved elastic performance. Traditionally this was horse hair, but hemp, straw and reed fibres have been used. More commonly fibreglass fibres or a plastic (nylon) mesh is used nowadays and even steel fibres can be used
- Additives: These are chemicals that are added to the mortar mix to alter the characteristics of the render. Common additives include silicon, polymers and acrylic. These are added to change the properties of the render, particularly the workability, elasticity, durability and the colour
The mixture of these component parts will determine the properties of the render.
Types of Traditional Render Finishes
The most common traditional render finishes include:
This is a render that is made with lime and it has the huge advantage of being both breathable and very flexible. This means that it is particularly suited to building which experience a lot of movement, such as timber framed buildings and older, traditional buildings.
Lime render is sometimes referred to as Traditional Natural Hydraulic Lime Render and has been traditionally applied to walls that have been built out of low quality stone or rubble, porous bricks, or where walls are exposed to driving wind and rain. The lime render does not create a barrier for the moisture but acts like a sponge and absorbs the water, stopping it passing through the wall by ‘sucking’ it up. This moisture will then evaporate from the lime render into the outside air when the weather turns.
Because traditional buildings that have been lime rendered have the moisture removed from them in this way, they can often tend to experience penetrating damp when the lime render is removed or replaced with cement render.
To strengthen the render, chopped hair was traditionally added and casein (an extract from cow’s milk) can be used as a plasticiser on difficult substrates. It is also possible to colour lime render to a wide variety of colours and shades. Lime render is seen as an eco friendly product as the curing process absorbs CO2 from the air as the render ‘sets’ to a limestone state.
There are a variety of ways that Lime render can be applied and these will be determined in part by the substrate and in part by the finish required.
In traditional buildings the render might be applied in a single coat, over a very rough and uneven substrate. In this case the render is almost used as very full flush pointing, with thick covering over the hollows and thin or sometimes no render over the stones of the wall themselves. To create a smarter and flatter finish more coats can be added and worked into a flat, even surface.
It is possible to use lime renders on a huge range of substrates including earth, stone, brick, timber framed buildings, stone or rubble filled walls, and straw bale walls. It can also be used on new builds that use all sorts of blocks, bricks, metal and fibre boards. It is very versatile as an external finish, and can also be used on interior walls too.
The Pros and Cons of using Lime Render
|Pros of using Lime Render||Cons of Using Lime Render|
Note that you should not confuse lime render with hydrated lime products which are used as a cement additive.
Sand and Cement Renders
These are renders that are typically made using Portland Cement (OPC – Old Portland Cement) and are much stronger and harder than any lime render. This type of render is typically painted.
Cement renders are not suitable for older buildings as the building construction tends to result in more movement which quickly causes cracking in the render. Additives (such as hydrated lime) can be used in the cement to increase the flexibility and durability but because this type of render is so hard it is always prone to cracking.
Like a lime render, cement renders are not waterproof so they are generally finished with finishing coat, typically paint, for protective and decorative purposes. Cement renders have been traditionally mixed on site, but increasingly now it is possible to purchase pre-packaged renders. These have the advantages of ensuring that the render is consistent which will help to reduce cracking, they are also easier to handle and can even be machine applied saving time and effort.
The huge advantages that a sand and cement render has is that they are cheap and they are also quick and relatively easy to apply. This makes them a popular choice, particularly in new build homes, where the movement is less and the substrates are firmer so reducing the propensity to cracking.
As a result of the potential for cracking there is more maintenance generally required with a cement based render. If there is any movement in the substrate or any moisture build up in the render it will cause the finish, typically paint, to become damaged and peel or flake away.
The pro’s and con’s of using sand and cement render can be summed up as follows:
|Pros of using Sand and Cement Render||Cons of using Sand and Cement Render|
Clay was the very first material to be used in renders and plasters and it is making resurgence lately due to its environmental credentials; it is very easy to produce and can often be locally sourced, although to ensure that the you use a render with predictable and consistent qualities it is wise to source a commercial clay render. There is minimal processing with makes a clay render much more environmentally friendly.
The characteristic that separates clay renders from the alternative cement or lime based renders is that it does not chemically cure (and therefore does not change its chemical composition ever once it goes off). As a result clay render can be re-activated by the addition of water, which means that it can be reworked; handy for repairs, but not so helpful as it will erode away.
Clay render will attract water and hold it. This is helpful if it is used against a wooden or straw substrate, however this can also prove a serious limitation should it be used with a modern substrate.
Traditionally binders such as straw can been added to the clay to improve its durability and resistance to erosion. To increase the ‘water proof-ness’ oils such as linseed oil can be added to the clay render. Adding an excessive amount of oil will reduce the water absorbency of the render and stop the permeability, preventing it from ‘breathing’.
The Pros and Cons of using Clay Render
|Pros of using Sand and Cement Render||Cons of using Sand and Cement Render|
Pebble dash does not specifically refer to the render but to the decorative finish that is applied to it. The wet mortar is coated with pebbles (sometimes called Spar although spar includes pebbles, chipping’s, shale and gravel) but the underlying mortar can vary.
Traditionally the mortar was a lime based, but it is more common now for cement to be used. There has been a growing use of polymer cements more recently but every type of mortar comes with various advantages or disadvantages over the other options.
The choice of mortar for pebble dashing will dependant on similar factors to those that affect the choice of a render that in not going to be coated.
Lime renders will be used in traditional building which move more and need the extra flexibility, or aesthetically it would look odd to anything but the existing render. Cement can be used where the substrate is suitable and the budget is limited. Polymer mortars can be used where a wider range of colours is required to increase the options for the spar (pebbles) that can be used.
When it comes to the different types of pebble dash that are used, there are a few. In recent times the practice of pebble dashing has fallen out of favour so none of these methods are used frequently any more, but these are the more commonly used:
- Wet Dash: Also known as roughcast. The chipping’s or spar are mixed into the final coat of the mortar which is then cast or sprayed on to the wall. This is one of the more traditional pebble dash type finished used in the UK
- Tyrolean Render: Tyrolean render is applied using a Tyrolean Gun to build up several layers. This is a cement based textured render which is ideal for covering old or poor brickwork. A Tyrolean Gun is a special bucket with a spindle in the middle rather like a hairbrush which can either be turned by hand or be powered
- Harl or Harling: This is a traditional render that is usually found in Scotland or Ireland. The harl is a mainly lime render so it cures rather than dries on the wall, is applied using a flicking method layering up until the desired effect is achieved. While the render is still wet pebbles are thrown into it and then pressed lightly into the render
Recently there have been technological advancements that have allowed new compounds to be used in renders. This allows you a wide range of finishes that have not been available before. Alongside these, new techniques have been developed that have altered the finishes that are available. Some of the most interesting are listed below.
Modern Polymer Render Finishes
These are cement based products into which specially developed polymers have been added to change to properties of the cement. There are two principle compounds that are used with polymer renders to improve their performance and increase their usability.
- Silicon: Silicon has a water repelling property that can be used to drive water away from the surface of the render but while still allowing the render and wall to ‘breath’ and let moisture pass through and out of the wall. Silicon water repellents are premixed into the cement or polymer render mix
- Nylon or Glass Fibre: Nylon and glass fibre is used in reinforced base coats, which provides a really strong base render before the finish coat is applied. A mesh, typically of nylon, is embedded into the base coat around the whole building. In some case this nylon base coat can be applied around stress points where cracking is likely, such as around windows and doors. The mesh is ‘breathable’ and quick to apply and provides the strength needed
There are some polymer renders that do not require a base coat. They are called monocouche or one coat renders. While they allow for quicker rendering there are limitations to the substrates that they can usually be applied to, typically only being used on lightweight or breeze blocks.
Modern Acrylic Render Finishes
Acrylic renders are finishing coat renders that are applied to achieve an attractive finish. It can be applied to a prepared substrate or to a base coat render and in some cases, to the existing render so long as it has been prepared properly.
These acrylic aggregates are added to the render mix to achieve an attractive finish in the desired colour. They can be sprayed on then applied with a float. Typically they will be applied to a base coat, but can also be used on well prepared brick and stone work.
Spraystone Render Finishes
Spraystone are typically acrylic exterior finishes that can be applied to any surface including glass and plastic (so you could even finish your pipe work to blend it with the render!) as they are highly flexible.
They are normally used for exterior finishes because they are breathable, like a porous paint, but they are light and can look exactly like a stone finish such as marble to granite. This means they can be used in places where a traditional stone finish would be too heavy or expensive, but they would produce exactly the same effect.
This is a relatively new type of idea and finish (certainly in respect to the UK market) so here follows a little more information on how it is applied:
Applying a Spraystone Finish
The substrate surfaces need to be carefully prepared and all windows and doors should be masked:
The prepared surface is then sprayed with a base coat that acts as a primer and provides the colour before the textured surface is applied.
Finally the textured surface coat is applied to create the desired effect. There are numerous effects that are available, mimicking almost all types of stone finish, both smooth and textured.
Benefits of a Spraystone Finish
The benefits of Spraystone are numerous; it is a highly flexible exterior finish that can be applied to almost any surface (even an old umbrella has been sprayed to create a granite effect!). It is also porous and breathable which means that it will not create issues with damp and moisture retention. The finish is incredible realistic, yet much lighter than real stone, meaning there are a lot of different applications that are available.
On the other hand, it is not really a DIY job as the application needs to be done carefully to ensure that the desired effect is achieved. While spraying is a quick way to apply the finish, it is vital that the preparation of the wall is thorough and any areas not to be sprayed must be masked properly.
For more information about applying less specialist render to the exterior of your home yourself, have a look at our project describing how to render exterior walls using more traditional methods.
External Wall Insulation
With more and more focus being put on saving energy, external wall insulation (EWI) is becoming a much discussed topic when exterior rendering is mentioned. By adding external wall insulation is it possible to reduce the heat that is lost from the building in cold weather (and gain in warm weather).
It does not take up space inside the building, as internal wall insulation does, so is seen as a popular choice when there are no cavities to fill with insulation. It is possible to use external wall insulation on a wall with a cavity, particularly if there is some reason that it is inappropriate to add insulation to the cavity.
Before the render is applied an ‘insulant’ is fixed to the wall, either with an adhesive or with fixings such as dowels and screws. The choice of insulant will depend of the level of insulation required, the thickness that is needed and your budget.
In some case it is necessary to extend the eves and overhangs to cater to the extra thickness being added to the walls.
The insulant or insulation is typically added in the form of boards or sheets, over which the render and finishing are applied. It is the render that provides the weather proofing and decorative covering.
Painting Exterior Walls on Your Home
Repainting your home or painting the render is a fantastic way to improve the look of the property relatively cheaply. It is an ideal DIY job say if you are getting ready to sell, or simply want to spruce the place up a little bit.
Generally there are no restrictions on painting a house as this is deemed a permitted development, however in some cases restrictions apply. If the house is listed the colour and style will be stipulated, if you live in a conservation area or National Park there can be restrictions and flats do not have permitted developments. If you do not own the freehold, you should check with the freeholder as they might have applied some restrictions.
Preparation for Painting Exterior Walls
The surface needs to be prepared before you paint. It must be stable and any blown brickwork or render will have to be repaired before you start. Prepare your wall for painting with these steps:
- Brush down the walls with a wire brush to remove any loose mortar, moss or mould. This should be easier if you have newly rendered the walls, but they will still need some preparation. All surface dirt, loose material or paint should be removed
- Fill all cracks with a suitable filler or render mix; the choice will depend of the render that has been used on the walls. For small cracks you can do this in one go with a filling knife which you can use to smooth off the surface. If the cracks are deeper than around 10mm then you should build up the filler in layers, allowing time for each layer to dry before applying the next layer. Once the filler has dried in the cracks it should be sanded back down so that it is smooth. If there are cracks that are sufficiently large or structural you should alert your building’s insurer
- Mask up the doors, windows and pipe work so that it doesn’t get covered accidentally while you’re painting the walls
- Priming the walls with a breathable primer is an important step. This is particularly important on porous and powdery surfaces so that you create a good surface for the paint to be applied. A breathable primer is necessary to ensure that the moisture in or coming through the wall and it’s render are allowed to escape. This is particularly important in solid walls as there is no cavity for this moisture to escape into.
How to Paint your Exterior Walls
Before you start any painting it is important to think about using ladders and safety while working at height. Please see our project on ladder safety here.
There are relatively few restrictions to the choice of paint that you are allowed, but it is important to ensure that the paint that you do select is breathable, which will not trap moisture underneath it inside the wall or the render. If the wall has been painted with an impermeable paint, and you are experiencing damp you will need to strip the walls before you apply a breathable paint.
As a general rule, textured paints are good for smooth renders, and a smooth paint is easier to apply to a rough surface, such as pebble-dash or Harling.
Steps for painting an exterior wall
- Check the weather forecast; you will need clear dry days in order to get the walls painted, so make sure that you have enough forecast so that you can get the whole job done in one go
- Divide the wall into manageable sections which you feel that you can complete in one session. Use features like downpipes and windows to guide you
- Lay out ground sheets and mask pipe work with newspaper before you start
- Get the right equipment:
- Masonry Brush – for cutting in and applying paint to areas the roller can’t reach
- Masonry roller – for tackling any large, flat areas with ease
- Extension pole – for attaching to roller to reach higher areas
- Paint kettle – for filling with paint to save on trying to hold large paint tins and containers
- Ladder or platform – for safely reaching higher area
- Start at the top of the wall and work down so that you are not splattering newly painted wall
- Use horizontal or vertical strokes to apply the paint. Apply the fully loaded brush to an unpainted part of the wall and then work back to the last painted part. Work over the painted surface in a variety of directions so that you get a good coverage and ensure that the surface is completely covered, particularly on a rough surface
- Stipple with the bush; on a rough surface the only way that you will be able to get the paint in to the texture of the wall is to hold it at right angles to the wall and then push the bristles, and paint, into the wall.
- Cut around downpipes and vent pipes. Ensure that you carefully paint behind the pipes with a brush
Dispose of any excess paint according to their instructions. See you local council website for how to dispose of paint correctly.
Exterior Finishes that Don’t Work
This candy stripped finish was ordered to be repainted after numerous complaints and mass coverage in the media. Kensington and Chelsea Council used section 215 under the Town and Country Act, usually invoked when a property’s “condition adversely affects the amenity of the area”.
Here are some more examples that are not regarded as hugely tasteful:
Changing your Home with External Finishes
There are numerous options available to the homeowner to improve their home with render and paint. Modern products have made it all the easier to achieve a dramatic finish without having to spend a small fortune. Improving your home’s exterior is a challenging but a very worthwhile project.
All project content written and produced by Mike Edwards