From Wikipedia, the free encyclopedia
Cement rendering is the application of a thin premixed surface ofsand, cement and lime to brick, cement, stone or mud brick. It isoften textured, coloured or painted after application. It isgenerally used on exterior walls but can be used to feature aninterior wall.
Depending on the 'look' required, rendering can be fine or coarse,textured or smooth, natural or coloured, pigmented or painted.
The cement rendering of brick, concrete and mud houses has been used forcenturies to improve the appearance (and sometimes weatherresistance) of exterior walls. It can be seen in different forms allover southern Europe. Different countries have their own style andtraditional colours.
Different finishes can be created by using different tools such as trowels ,sponges, or brushes. The art in traditional rendering is, (apartfrom getting the mix right), the appearance of the top coat.Different tradesmen will have different finishing styles and be ableto produce different textures and decorative effects. Some of thesespecial finishing effects may need to be created from a thinfinishing 'top coat' or from a finishing wash.
There are also a wide variety of premixed renders for different situations.Some have a polymer additive to the traditional cement, lime and sand mixfor enhanced water resistance, flexibility and adhesion.
Acrylic premixed renders have superior water resistance andstrength. They can be used on a wider variety of surfaces, includingconcrete, cement blocks, and AAC concrete panelling. With the rightpreparation, they can be used on smoother surfaces like cement sheeting,new high tech polymer exterior cladding such asUni-Base, and expanded Polystyrene. A few of these require activationwith cement just prior to application.
Some of these premixed acrylic renders have a smoother complexion thantraditional renders. Others can even be spayed on.
There are also a wide variety of acrylic bound pigmented 'designer'finishing coats that can be applied over acrylic render. Dependingupon the product, they can be rolled, trowelled or sponged on. Alimited number can also be spayed on. Various finishes, patterns andtextures are possible such as sand, sandstone, marble, stone, stonechip, lime wash or clay like finishes. There are stipple, glisteningfinishes, and those with enhanced water resistance and anti fungalproperties. Acrylic renders take only 2 days to dry and cure - muchfaster than the 28 days for traditional render.
To ensure adhesion, the surface to be rendered is initially hosed off to ensureit is free of any dirt and loose particles. Old paint or old renderis scraped away. The surface is roughened to improve adhesion. For largeareas vertical battens are fixed to the wallevery 1 to 1.5 metres, to keep the render flat and even.
Cement render consists of 6 parts clean sharp fine sand, 1 part cement and 1part lime. The lime makes the render more workable and reducescracking when the render dries. Any general purpose cement can beused. various additives can be added to the mix for increasing adhesion.Coarser sand is used as the base layer and slightly finer sand for the toplayer.
- Plaster, Render, Paint and Coatings: Details, Products, Case Studies (Detail Practice) by Alexander Reichel, Annette Hochberg, and Christine Köpke (Jun 28, 2005)