Basics of Rendering A Wall with Sand & Cement
If you’re looking to protect your walls against the elements, and let’s face it, here in the UK we do get some pretty harsh weather conditions, applying render is a pretty good way of doing so. Not only will it protect the wall against harsh weather, it will also provide an aesthetic appeal and will help to really improve the appearance of the wall itself. Small scale rendering can be done yourself, although it’s highly recommended that you speak to a professional builder and get their opinion, and perhaps their help, before you take on any rendering work yourself. Here’s a very basic step by step guide on how to render a wall using the traditional sand and cement/lime method.
Prepare the wall for rendering – If it has been rendered in the past, and that is now chipping and falling away, remove as much of the old material as you possibly can. Once you’re happy that all of the previous render has been removed, use a hosepipe or pressure washer and remove as much of the dust and debris as possible.
Now would be a good time to examine what you will be rendering. Are the bricks soft and crumbly? Are there lots of cracks in the brickwork? You should take the time to prepare the base properly and do any remedial repairs before continuing. Do not skimp or try to save money on this stage as it will only cost you more time and money in the long run. Cracks can be repaired with mesh or specialist methods before rendering over. New rendering should not be applied directly to ‘dry’ surfaces which have not been coated with PVA or Gripbond type liquids which stop the render drying out too quickly and helps adhesion.
Mixing Render – Render actually only contains three ingredients, and they are lime (stone, not the fruit!), water, and sand. Occasionally however, Portland cement is substituted in place of the lime, which will make it stronger, but slightly less breathable. Hydrated lime should be used, with 1 part lime being mixed with 3 parts sand. Ensure that the sand used has sharp and angular grains, rather than fine and smooth grains. Masonry or plasterers sand is by far the best. There are also many additives available for waterproofing and plasticising (making the mixture more workable) speak to your builders merchant for recommendations.
Great care should be taken when mixing and the ‘ingredients’ should be properly gauged to ensure correct amounts are used and thoroughly mixed using a cement mixer.
Apply a scratch coat of render – Render should be applied in 2 layers, and the very first layer is what is known as the scratch coat. Apply it carefully to ensure that it really sticks to the wall as efficiently as it can. Using a trowel, smooth it as evenly as possible across the wall followed by a ‘Darby’ or straight edge to ensure the first coats is a flat as possible. This will make it easier to apply the next coat and get it looking nice and smooth.
As soon as the first layer is applied, but not yet set, you should scratch the wall using a rendering comb for large areas or a piece of wood with nails knocked through for a small area to get the surface ready for the next layer. This will provide a rough surface for the next layer to adhere itself to.
Apply the finish layer – When the first layer is set and has been scratched up, you should again wet the wall and apply the next layer in the same way as you did the last. This layer of render should be a weaker mix than the first. But this time you should finish off the rendering with a plastic or wooded float before it has gone off completely if you are trying to achieve a smooth finish.
This is only a very, very basic guide and although it may sound simple enough to render a wall. Rendering can be very heavy work and difficult to achieve a good finish that will last years. Weather conditions also play a big part in successful rendering and should not be done either in freezing or hot weather.
It really is worth getting expert advice from a professional before you undertake any work you’ve never done before.