Cement render
Cement render or cement plaster is the application of a mortar mix of sand and cement, (optionally lime) and water to brick, concrete, stone, or mud brick. It is often textured, colored, or painted after application. It is generally used on exterior walls but can be used to feature an interior wall. Depending on the 'look' required, rendering can be fine or coarse, textured or smooth, natural or colored, pigmented or painted. The cement rendering of brick, concrete and mud houses has been used for centuries to improve the appearance (and sometimes weather resistance) of exterior walls. It can be seen in different forms all over southern Europe. Different countries have their own styles and traditional colors. In the United Kingdom, cement is optional. In other countries, lime is optional. The cement in render hydrates the same way it does in concrete. Render finishes Different finishes can be created by using different tools such as trowels, sponges, or brushes. The art in traditional rendering is (apart from getting the mix right) the appearance of the top coat. Different tradesmen have different finishing styles and are able to produce different textures and decorative effects. Some of these special finishing effects may need to be created with a thin finishing top coat or a finishing wash. Traditional rendering Cement render consists of 6 parts clean sharp fine sand, 1 part cement, and 1 part lime in some parts of the world. The lime makes the render more workable and reduces cracking when the render dries. Any general purpose cement can be used. Various additives can be added to the mix to increase adhesion. Coarser sand is used in the base layer and slightly finer sand in the top layer. The application process resembles the process of applying paint. To ensure adhesion, the surface to be rendered is initially hosed off to ensure it is free of any dirt and loose particles. Old paint or old render is scraped away. The surface is roughened to improve adhesion. For large areas, vertical battens are fixed to the wall every 1 to 1.5 meters, to keep the render flat and even. Acrylic rendering There is also a wide variety of premixed renders commercially available for different situations. Some have a polymer additive added to the traditional cement, lime and sand mix for enhanced water resistance, flexibility and adhesion. Acrylic premixed renders have superior water resistance and strength. They can be used on a wider variety of surfaces than cement render, including concrete, cement blocks, and AAC concrete paneling. These acrylic modified renders may still be too brittle and cannot be applied over substrates like fiber cement sheeting, as they will crack on the joints and can allow water to enter the sheet and cause delamination of the coatings. The newer technology polymer exterior cladding such as expanded polystyrene (EPS) can have these acrylic modified renders applied to them with the inclusion of an alkali resistant mesh encapsulated between the render coats. Some premixed acrylic renders