The Best Weather Conditions for Rendering

Things don’t always go according to plan when working on a construction site, and sometimes, weather conditions can affect your ability to start rendering. The ideal temperatures for installing render vary between manufacturers. For EWI Pro renders, the best weather conditions for rendering include temperatures between +5 and +25 degrees Celsius.

This isn’t to say that an unprecedented heatwave should halt all work, as temperatures can reach over 25 degrees in the summer. Renderers must find ways to work around the heat; the same goes when the weather’s cold.

So here’s our advice on what to do when the weather conditions aren’t ideal for rendering!

Weather conditions for rendering – hot weather

We always advise against using our materials in temperatures over 30 degrees. Most especially, if it’s a warm day, it’s best not to render it in direct sunlight. This is the most probable cause of the render drying out too fast, resulting in cracking, damage, or even a patchy finish. High temperatures can cause the render to dry too quickly. Fast drying can prevent the render from bonding properly with the substrate, leading to long-term durability issues. Moreover, if the render dries unevenly, it can result in a patchy appearance or visible cracking, compromising the finish’s structural integrity and aesthetic quality.

Tips for rendering in direct sunlight

• Start before the sun has fully risen
• Apply to walls in the shade
• Apply a water-based primer
• Use covers to provide shade
• Embed Fibreglass Mesh to the system

Start before the sun has fully risen

Many renderers use an old trick to start before the sun has fully risen (many of our installers start at around 5 a.m.!). Start by applying on a wall that is not exposed to sunlight. Then, follow the sun around the building, working on the walls in the shade. This allows you to continue to work in sunny weather but prevents issues with the render drying out too fast in direct sunlight.

Apply to walls in the shade and use covers

Erecting temporary screens or scaffolding with protective sheeting can shield the render from direct sunlight. This control over exposure is crucial to prevent the rapid evaporation of water from the render. Besides physical covers, ensuring the rendered surface remains moist can aid in proper curing. Regular misting with water can be effective, especially after the initial set.

Apply a water-based primer

A Water-Based Primer limits the substrate’s absorptive capacity. Ordinary masonry will have dried out during hot weather, and the substrate’s absorptive capacity will be extremely high. Using a primer prevents the substrate from absorbing too much water from the render, causing it to crack during curing.

Embed fibreglass mesh

We always advise using Fibreglass Mesh embedded within the basecoat layer for our thin coat render systems. We also advise that mesh is embedded within the first layer of Monocouche. This is even more essential when the weather conditions for rendering are not ideal, as the Fibreglass Mesh increases the tensile strength of the whole system. So, when the render shrinks during drying, the mesh will help prevent cracking. Use render mixes adjusted for high temperatures, which might include slower-curing additives that compensate for the quick drying caused by the heat.

Pro tips for professional results

• Monitoring Weather Conditions: Always monitor the day’s forecast and real-time temperatures. This will help you adjust your working practices and timings as needed.
• Hydration: Ensure all materials, especially the substrate, are sufficiently hydrated before application. This might mean pre-wetting the surface in extremely dry conditions.
• Professional Consultation: Consult manufacturers about the best products and practices for rendering in high temperatures specific to your region. They may recommend specific additives or mixes designed for such conditions.

Weather conditions for rendering – cold weather

The primary concern when rendering in cold weather is the effect of temperature on curing. Render needs a certain level of warmth to cure correctly; without it, the water in the render can freeze, expanding and causing the render to crack or flake off. Additionally, cold weather can make the substrate more brittle and less absorbent, which compromises the bond between the render and the wall.

Tips for rendering in cold weather

• Timing
• Material adjustments
• Use protective measures

Timing

Always monitor the weather forecasts to avoid rendering during sub-zero temperatures. It’s advisable only to apply render when the temperature is above 5 degrees Celsius and when no frost is predicted for at least the next 24 hours. Like with hot weather rendering, timing is crucial in the cold. Take advantage of the warmer daytime temperatures and natural sunlight, which can help in the initial curing of the render.

Material adjustments

Many render manufacturers offer products with accelerators ideal for use in colder temperatures. These accelerators help speed up the chemical reactions that cause the render to set and cure, reducing the risk of damage from freezing temperatures. For example, our EWI Pro Render Accelerator can cut overall working time in half! Storing render materials in a warm environment before use can prevent the shock of cold materials on a cold substrate, which can slow down curing times excessively.

Protective measures

Employing heating lamps or insulated covers can create a microenvironment conducive to curing. These tools can maintain a stable temperature around the newly applied render, shielding it from the cold and helping it to cure properly. In dry and cold conditions, substrates can become highly absorbent, pulling moisture out of the render too quickly and weakening the bond. Lightly dampening the substrate can help manage this issue.

Pro Tips for Professional Results

• Layer Thickness: Apply thinner layers of render. Thinner layers are less likely to retain moisture that can freeze, reducing the risk of frost damage.
• Continuous Monitoring: Using thermometers, constantly monitor the temperature of the air and the substrate to ensure conditions remain within safe limits.
• Consultation with Experts: Always consult render manufacturers about the best products and techniques for application in cold weather. They can provide guidance on specific mixes that are formulated to perform better under such conditions. The EWI Pro Technical Team is always available to assist with such queries.

So, what are the ideal weather conditions for rendering?

The ideal weather conditions for rendering are typically found in spring and autumn. These seasons often provide moderate temperatures and reduced intensity of sunlight that are optimal for rendering projects.

Temperatures between 5°C and 25°C are ideal for rendering. This range helps ensure that the render dries and cures at an appropriate rate, avoiding the rapid drying caused by higher temperatures that can lead to cracking and other defects. The cooler weather in spring and autumn helps maintain these moderate temperatures throughout the day.

Spring and autumn usually offer more consistent weather patterns without the extreme conditions often seen in summer and winter. This stability is crucial for allowing render to cure properly. Sudden temperature changes and extreme weather can negatively impact the curing process. The relative predictability of spring and autumn weather is a significant advantage.

The sun is less intense during spring and autumn, which is beneficial when rendering. Direct sunlight can cause the render to dry too quickly, leading to a patchy finish or even cracks, as the material doesn’t have enough time to bond properly with the substrate. The softer sunlight in these seasons helps prevent these issues.

While spring can sometimes be wet, periods of dry weather are also common, which are essential for rendering. Render needs time to dry without being washed away by rain. Autumn often offers dry spells, which are perfect for applying render. It’s important to check the local weather forecasts to choose the best dry period within these seasons.