Options for rendering. Who knew?
There are many benefits to rendering a house, either to cover up existing ugly brickwork or just because you fancy a more modern contemporary finish on your house. Whatever your reasons for rendering, it is important to be well-informed on the different types of rendering options and to be able to make an informed decision when it comes to the right one for your self-build project.
The aim of applying render to a new building is to provide external walls with a strong, and visually attractive finish. More importantly, when it comes to Building Regulation requirements, render can offer an extra layer of water protection and also improve the Fire Rating of a building. However it is important to note that not all renders are designed to be waterproof.
Traditional Rendering Methods - render can be prepared from a number of easily accessible materials on site such as cement, lime or clay. In the main these are not waterproof and by their design will absorb water and release moisture back into the atmosphere over time after rainfall.
Cement based render for example, was applied to buildings constructed in the 1900s, consisting of a mixture of water, cement and sand all materials were readily available on site, meaning the method of preparing and creating a smooth, aesthetically pleasing finish to walls was low cost. Applying render was also relatively simple, often applied using a trowel in thin layers providing a strong and hard finish to a wall.
The downside of using traditional renders was that the render often took up to 28 days to dry and that in the main these are not waterproof and by their design will absorb water and release moisture back into the atmosphere over time after rainfall.
You may be “forced down” this route if say the building is listed but to “finish” the render, a paint system needs to be applied to provide the waterproof finish. Although the finish was strong, render often proved to be inflexible, prone to cracking due to weathering or shrinkage of the building.
New Technologies – today, modern methods of construction have seen advanced render products become readily available to the market offering vast improvements concerning the problems associated with traditional renders as described above.
However, these come with their own problems. The most notable of these improvements is that the drying time of the render once applied has now dramatically reduced, with some ‘ready-made’ mixes taking as little as twenty-four hours to dry. The advantage of this is two-fold, with a reduced drying time works on site can finish quicker and the impact of the weather on drying render is diminished as the timeframe of exposure for drying has greatly decreased. Modern renders are also now available in a range of colours, negating the requirement to paint over the top of dried render, again saving on time and labour costs. Technology in the render (for example silicon) has now made the product more porous and flexible, allowing the building to ‘breathe’ reducing the possibility of cracking. Beading can be used at corners, around doors and windows (stop beads) and finishing the render above the DPC (bellcast beading). so as to stop bridging and water ingress.
What to watch out for:
Ensure the render you are using is suitable for not only the property but also its location and environment.Traditional renders do still have their place.
Ensure the render is compatible with the backing material such as render boards, and the board is compatible with the substrate.Ensure the system has some form of testing criteria such as Agrément certificate.These are issues by the British Board of Agrément after substantial testing and will test the system as a whole.Many Warranty providers will require this.
If the render is designed to be porous, ensure the backing material is also designed to be porous or there is an open cavity. Design in the fact that the moisture will need to go somewhere!
Incorrect backing materials can act as sponges soaking the boards and over time water penetrating through to the cavity. On a timber framed buildings this essentially begins the process of rotting the frame of the building from the inside out causing structural failure.
Design in movement joists, stop beads and castings to deflect water away from the structure so as to reduce water ingress.
With any render, use an experienced or specialist contractor who fully understands both the product, the building and what you are trying to achieve.The majority of warranty claims are failures as a result of poor workmanship and design and not the product.Often these Contractors are approved by the material supplier and will apply the render according to their instructions.