Laboratory testing was used to assess the performance of four proprietary external renders under UK conditions. Ready-mixed dry renders are supplied in bags and require only the addition of water before use. Ready-mixed (or premixed ) renders are also supplied dry, but require additions of both water and other material ( such as cement or sand ) prior to use. Retarded ready-to-use renders are delivered to site with water added and ready to use. The render samples, which included polymer-modified cement:sand, with and without fibre additions, were applied to walls of common clay brick and of low density lightweight aggregate concrete block. Compared with traditional site-mixed render, the proprietary materials exhibited enhanced bond strength, resistance to water penetration and freeze/thaw durability. However, the water vapour permeability was lower. 2 refs.