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The render mixture can make or break how good a rendered surface turns out. Most render mixtures contain water, cement, sand and lime. However, how a render mixture turns out depends on various factors, including the ratio of the materials and the quality and texture of the sand and cement used.

Continue reading to learn more about the render mixture and how different factors can affect the quality of the render mixture.

Components of a Render Mixture

What makes up a render mixture?

  • The standard cement render mixture is made up of sand, cement, water and lime.
  • Acrylic renders are made of lime, sand, and acrylic resin.
  • Silicone renders combine a cement-based render with an addition of silicone resins.
  • Polymer-modified renders are made of acrylic resin and polymer.
  • Lime render is made from a combination of lime and sand.

What Are the Best Ratios for Render Mixtures?

The best ratios for render mixtures are six parts sand, one part cement and one part lime. Some renderers may neglect to add lime to their render mixtures, which can be a mistake.

Lime in render mixtures makes the render self-curing and holds up much better than plasticisers, which are used as an alternative.

A simple rule of thumb is to never make the rendering mix stronger than the material you are rendering. The render must bond well with the surface to be flexible enough to withstand the building’s natural movement over time without cracking.

The Ideal Thickness for a Render Mixture

The typical thickness of render mixtures ranges from 10-15 mm, but this can differ depending on multiple factors. A maximum thickness of 12.5 mm for a single-coat render is recommended, while a double-coat should be no more than 15 mm. The thickness of a render mixture can have an impact on the strength, durability and quality of the render.

Thinner render layers can result in cracks and reduced durability, while thicker layers can result in shrinkage or cracks. It is essential to use the correct thickness for the material you are applying the render to.

Ensure that you take climate and environmental factors into consideration.

Render Layers

The first render layer (base coat or scratch coat) should be applied at a thickness of 4-6 mm. After the first coat of render has been applied, it needs to be left alone to dry and cure before applying the second layer. Repeat the steps before applying a third coat (if desired).

Applying the render in multiple layers can result in a stronger bond with the surface and reduce the risk of cracks forming.

Naturally, if your render is textured or patterned, more than two render coats or thicker render layers may be required to achieve the desired effect.

Factors to Consider When Determining the Thickness of Render

Render Mix

Having a higher ratio of sand in the render mixture results in a stronger render, which means you only require a thinner coat. A higher cement ratio may result in a thicker coat for strength and durability.

Surface Material

Different surface materials require different render coats for the best outcomes.
Uneven surfaces or surfaces like bricks need a thicker render coat to cover up any imperfections or completely cover coarse surfaces. Meanwhile, evener and smoother surfaces require thinner coats of render.

Application Method

How the render is applied can also have an impact on the thickness of the render. Using the traditional, manual application method (a trowel and hawk) may result in differing layers of thickness.

Using more modern application methods like spray rendering may result in a more even, smoother surface.

Various tools like floats, sponges, and trowels can also help achieve thinner, smoother coats.

The Environment and Climate

In warmer climates with lower humidity levels, multiple thin coats of render may be necessary for better curing and hydration.

Wetter climates with higher humidity levels require thicker render layers for water resistance and durability.

Factors to Consider When Using Thinner Render Layers

If you’re planning on using thinner render coats, here are some important factors to consider:

  • Faster drying times: Thinner render layers naturally take quicker to dry due to the speed at which the moisture evaporates from the render.
  • Reduced curing time: Thinner render coats also require a shorter curing period, as the chemical reactions needed for curing can take place faster.
  • Structural strength: Thinner render layers put less pressure on the building’s structure, keeping it stable and strong.
  • May not provide enough protection or durability: Thinner render layers may not be as protective or durable as thicker render coats.
  • May not result in the desired effect: Thin render coats may not result in the desired effect, especially if you plan on having a textured or patterned render.
  • May be more susceptible to damage: Thinner coats of render may be more prone to damage or imperfections forming.

Factors to Consider When Using Thicker Render Layers

If you plan on using thicker render coats, here are some important factors to think about:

  • Longer drying times: Thicker render layers need more time to completely dry as there is more material to dry and moisture to escape from.
  • Longer curing period: It will also take longer for thicker render layers to cure due to the excess materials.
  • Impact on structural strength: Having thicker render layers can add extra weight to the building structure and have a higher risk of cracking or shrinking.
  • Less effective bonding: Thicker render layers can have more difficulty bonding with the surface and may need extra reinforcement or bonding agents.
  • Improved water resistance: Thicker renders have superior water resistance to thinner render layers. Thicker render layers provide a more effective barrier to water and moisture.
  • Requires more finishing work: Thicker render layers may require extra work and time to produce a more neat or uniform finish. Any imperfections are more noticeable.
  • More resistant: Generally, thicker render layers are more resistant to imperfections or damage.

At Sydney Cement Rendering, we take pride in being Sydney’s trusted rendering experts, providing our customers with the highest-quality rendering services. Contact us at 0402 704 984 or visit our website: https://sydneycementrendering.com/ to find out more about what we offer!