Renders consist of a variety of ingredients, the amounts of which will determine its eventual characteristics and application. Usually, the render’s name will reflect the main ingredient.
Individual components of render are:
- Binding Agent: Usually derived from lime, cement, clay or gypsum, the binding agent acts as the glue that holds the render together. It provides strength, permeability and offers resistance to moisture.
- Filler: Typically sand is used as well as other aggregates and makes up the largest part of the final render.
- Water: Creates an applicable format to the render and activates the binding agent.
- Fibre: Added to create elasticity and strength, ‘fibres’ are added. Traditionally these would have been horse hair or straw, although modern renders will use fibreglass or nylon and in some instances steel fibres.
- Additives: Modern renders contain additives to alter the properties to make it suit a particular function. These can include silicon which makes it more elastic, durable and waterproof. Colour is also an additive and can drastically alter the final effect.
The mixture of these component parts will determine the properties of the render.