The main components of bagged render are sand and cement. Water is added to not only mix the render, but also to create a chemical reaction. This is referred to as ‘hydration’. Once the render is applied to a substrate, the water assists in curing the render, and what is not needed for curing, evaporates into the atmosphere. However, in dry weather (even in cooler conditions), the render may dry too quickly and as a result, not have enough water retained within the render to cure properly. This lack of hydration can cause the render to become soft and powdery.
To avoid render not curing properly and becoming soft and powdery, ROCKCOTE recommends that applicators wet down walls prior to the application of cement-based renders and continue to re-hydrate the render once it is on the wall for 2-3 days after application. In dry weather the substrate draws the water from render faster than in more humid conditions, so wetting down the walls prior to application reduces this suction. In addition, once the render is applied and has begun to harden, applying a light mist of water will assist the hydration process. Re-hydrating the render at least once a day for 2-3 days after application will also help ensure that the cement-based render cures properly. This is particularly important in dry and/or windy weather conditions.
The time that it takes render to cure properly is commonly lengthened by cooler temperatures. For example, at 5°C it takes standard concrete 5 days to achieve the same strength as 1 day at 40°C. This should be taken into account when planning projects.
Acrylic render does not cure with a chemical reaction like cement-based render. However, acrylic renders can still take longer to dry than stated on the products’ TDS (based on 25°C, 50% relative humidity).
Selected ROCKCOTE Coloured Renders and acrylic textures are available in ‘Winter Grade’ formulations, which are advised for use in cold climates for reduced drying times. These Winter Grade formulations are available for: