Modern renders

In both new construction and refurbishment, houses can be rendered for one or more of the following reasons:

   to prevent damp penetration
   to provide a decorative finish
   to hide poor quality bricks, blocks or stonework
   to improve thermal insulation.

Modern renders are a mix of binders (cement/lime) and aggregates (sand), applied in one, two or three coats. The number of coats is dependent on the choice of render system, the nature of the background and the exposure of the building. The top coat can have a smooth finish, a textured finish or can contain a coarse aggregate to give a variety of decorative effects. Chemicals can be added to the mix to provide increased plasticity, flexibility or improved waterproofing qualities.

Rendering is a highly skilled trade, requiring not only a high level of technique but also a thorough knowledge of materials, together with an understanding of how these materials will perform in what is often a very exposed situation. Concerns regarding consistency, efficiency and long-term durability of self-mixed renders have led to the development of pre-mixed polymer renders and synthetic thin coatings. Although they still require a high level of skill in application, their use has reduced the risk of inappropriate or ill-informed material and proportion selection inherent in self-mixed renders. Pre mixed renders are detailed towards the end of this chapter. The materials and principles of rendering are considered in the following section.