In the UK we often think of weather issues as being something at the other end of the spectrum – too cold, too wet or too windy to work – rarely do we ever highlight the fact that it's too sunny! It’s important to keep an eye on temperatures when working outdoors as keeping yourself and your materials cool is essential on any project.
Hot weather in particular can cause cementitious materials to go off much quicker than usual. Render that stiffens too quickly can become weakened, as the cement has not given time to hydrate fully and reach its full strength. For Weber renders, application should not be carried out at temperatures above 30°C, and it’s important to check the temperature of the substrate before applying – not just the air temperature as retained heat will affect freshly applied mortar.
If the substrate needs cooling, this can be done by giving it an even mist of clean water. Be careful to avoid saturating the substrate, as this can lead to cracking, and a poor bond of the render to the blockwork.
If rendering in the heat, application should always be carried out in the shade, making sure you follow the sun around the building. In hot, breezy and rapid drying conditions, it may be necessary to actively cure the render by misting it twice daily for three days after application.