Wetdash (Roughcasting or Harling)

Produced by throwing a wet mix of granite chippings (usually 6mm to dust) and cement (1:1 mix) against the smooth towelled (but not floated) top coat of render whilst it is still green. The roughcast mix can be modified with sand to give the required consistency. Traditionally this mix was ‘knocked up’ first thing in the morning adding lime instead of sand. It was left to stand for around 2-3 hours whilst coating went ahead. The applicator then applied the cured mix to the wall. Roughcasting using wet products can prove to be a messy application requiring large amounts of on site cleaning after the application. Modern pre-mixed roughcast products are now available that require mixing with clean water to create a similar finish to the original products.

Smooth Float Finish

Produced by rubbing the towelled surface of the render using a wooden (or plastic) float or sponge to give a smooth finish. This is done after the top coat has taken up and become ‘green’. As the floating action draws the weak laitance (cemetitious liquid) to the surface, there is a tendency for cracking to occur while drying is taking place. For this reason float finish is usually associated with masonry paint finishes which fill the fissures (small cracks) and help prevent damage. The extent of cracking is usually related to the shrinkage characterises of the sand.

Pre Mixed Render Finishes

Pre-mixed renders are available in a wide range of colours. Often silicone and algae inhibitors are included within the mix at the factory production stage. Care should be taken to ensure the correct amount of clean water is added at the on site mixing process that involves blending the pre bagged render with water and mixing with a paddle mixer. It is essential that coloured render is used from the same batch (think matching wallpaper rolls!) to ensure the colour of each batch is the same. Usually this finish would be given a light textured or scraped textured finish using trowels designed for this purpose. Fibres of polycarbonate are sometimes used within the mix to improve crack resistance and integral strength. Polymers in the powder form to improve the bond strength and extensibility. The use of lightweight aggregates minimise the chances of shear problems and improve the application. The advantage of factory batched, dry bagged mortars are that they are easily used on site and maintain a constant standard of batching, pigmenting and purity.

Thin Coat Renders and Paints

Designed as a top coat finish that is from 1.5 to 3mm thick. Mainly specified on new build and commercial applications sharp clean finishes are enhanced with this type of finish. With the base coat applied by trowel finish the paint is applied by roller or brush. Many of the paints used contain high amounts of silicone that act as a water repellent helping the building to remain clean looking for longer. These products normally require application by specialist companies given the complexities of application. The rules that relate to what weather any render product can be applied especially applies to this type of render as sudden changes in temperature and moisture can affect how the product cures.