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HSNF made Renders
The rendering of exterior walls is a process that has taken place over hundreds of years and was certainly used by the ancient Romans. Most hand made renders consist of lime and sand and different sources of information do not always agree on the exact quantities of each. Very often hand made renders tend to be a process of trying things out until you find something that works, what most sources agree on is that you shouldn’t allow a lime render to dry to quickly as it may shrink and not provide adequate cover for your walls. Some sources recommend only one coat of render while others argue that two or three are needed. If you are getting involved in hand made renders then it is a good idea to do some research and find out all you can about plaster work as it is not always clearly defined.
Mixing and Preparation of Renders
You can either make an aggregate or mix of lime and fine pit sand but it is also possible to use lime on its own as it has been done that way for hundreds of years. Some renders are made of clay and mixings can be hard or soft depending on what you are trying to achieve with hand made renders. Your top coat should be finer than the base coat and don’t worry if there are cracks in the base coat as these are usually covered well with second and third coats. You need to make sure that the undercoat has dried before you apply extra layers. When done properly lime renders can help to protect your exterior walls from the weather and may also stem any rising damp. Before you begin to apply any of the hand made render to your exterior walls you need to ensure that the surfaces are thoroughly cleaned and well prepared. You should treat any mould spots with a fungicide before you apply your render to the surface.
Applying Hand Made Renders
You should not apply render to a dry surface. Make sure that the walls are damp when you make the application with either a brush or a trowel as this prevents the wet render from soaking into the substrata. If you find that the first coat of rendering is shrinking as it starts to dry, you can deal with this by using a plasterer’s float and damping the wall again.
Drying Lime Renders
You shouldn’t let lime renders dry too quickly or it will fail and may not adhere properly to the substrata. The second coat of render should be applied about a week after the first, before the initial one has completely dried out as this can help to strengthen the render as a whole – if you apply second and third coats too soon after the first this can result in more shrinkage and a render that is not properly attached to the substrata. The final coat should be between 5-7mms and no thicker.
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