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Sand and Cement Render: Experts in External Rendering | Colourful Monocouche Solutions

Updated July 9, 2024
Perfect for UK homeowners looking to enhance their home's exterior with durable and attractive rendering.

Sand and Cement Render

Reflect on these four scenes:

  1. Majestic Roman houses and temples from millennia ago.
  2. Sparkling rows of white homes on breath-taking Greek islands.
  3. Charming cottages in pink, white, blue, or yellow in idyllic English villages.
  4. Modern homes with walls in crisp, clean hues.

What ties these scenes together? They all feature render to enhance their appearance! However, rendering is not solely for aesthetics. From ancient Roman times to today, sand and cement render has been a reliable method to shield buildings from severe weather conditions.

Temperature changes make walls expand and contract, leading to cracks that let moisture in. Freezing weather makes this worse by forming ice that widens the cracks. Porous materials like brick, stone, or concrete blocks allow water to seep through, causing dampness inside. Problems such as mold, mildew, rising/penetrating damp, and rot can arise.

Applying a layer of render to your home adds a protective barrier that prevents weather damage and lowers the risk of damp issues, while also improving insulation. Rendering also boosts curb appeal, adds value to your home, and hides unsightly wall surfaces.

If you're considering rendering your home, this guide will give you an overview of what to expect. Small projects can be handled independently, but seeking professional advice is wise. For larger projects, it’s best to hire experts like Midrender to ensure optimal results.

The Rendering Process

Preparing the Walls


Existing walls may have old render that is chipped and cracked with bare patches. Unrendered walls might be dirty, have plants and algae, or spots of grease, oil, and paint. These must be fully stripped and thoroughly cleaned. The wall should be hosed or sprayed to remove debris and dust.

Inspect the wall for crumbling bricks or masonry. Remove loose mortar, brick, and other materials, and fill gaps and cracks to create a level surface for the render.

Preparing the Mix


The traditional render mix uses 6 parts sand, 1 part cement, and 1 part hydrated lime. Lime adds elasticity, preventing cracks and crumbling once dried (or cured).

The sand and cement type affects the mix’s strength, efficiency, and final appearance. Building sand causes shrinkage and cracking; use sharp sand or rendering/plastering sand instead. Adding a waterproofing agent increases protection and extends the render mix's working time, useful for large areas. Some prefer a mortar plasticizer over lime, but both improve workability. Lime is often preferred as it adapts with the building, is more breathable, and naturally fills hairline cracks.

For cement, any general-purpose brand from builders merchants works, but better quality ensures better results.

Preparing the Mix

The traditional render mix uses 6 parts sand, 1 part cement, and 1 part hydrated lime. Lime adds elasticity, preventing cracks and crumbling once dried (or cured). It's essential to get the right mix; too wet and it will run, too dry and it will be hard to work with. Add water in small amounts until the mix has the right consistency.

The sand and cement type affects the mix’s strength, efficiency, and final appearance. Building sand causes shrinkage and cracking; use sharp sand or rendering/plastering sand instead. Adding a waterproofing agent increases protection and extends the render mix's working time, useful for large areas. Some prefer a mortar plasticizer over lime, but both improve workability. Lime is often preferred as it adapts with the building, is more breathable, and naturally fills hairline cracks.

For cement, any general-purpose brand from builders merchants works, but better quality ensures better results.

Applying the Render

Begin with a thin base coat, or scratch coat. Apply by hand with a trowel or spray, pushing it tightly into gaps and cracks, ideally 3 to 5 mm thick. Use a straight edge (Darby) to smooth the surface. Before the mixture dries, scrape the surface with a rendering comb.

After the first layer sets (usually one or two days), apply the next coat with a weaker mixture. Lightly spray the dried surface with water before applying the render to help the second coat adhere. Trowel on the mixture and smooth it down with a rendering float.

Various finishes can be created with different tools and techniques:

  • Textured finish: Add coarse sand to the final mix.
  • Sponge finish: Use a sponge to dab the surface (ensure it’s not too wet to avoid streaks).
  • Patterned finish: Roll a balled hessian bag across the damp surface.
  • Trowel finish: Use a wooden float for a fine, smooth finish.
  • Roughcast finish: Flick the mix onto the wall, sometimes adding crushed aggregates. Traditional Pebbledash is similar but adds aggregates to wet cement rendering afterwards.

Do I Need A Scratch Coat?

Most experts agree that a scratch coat is essential. A scratch coat is a thin layer of plaster, render, or mortar (no more than 5 mm thick) applied to the wall surface and scraped with a comb to form grooves before it dries. These grooves help subsequent layers adhere, forming a strong bond that adds strength and stability when dry. Without it, the render might slip while curing or form air gaps, leading to cracks and detachment.

Is A Cement Mixer Best?

Using a cement mixer ensures the sand and cement render is mixed evenly. Mixing in wheelbarrows is less effective and can leave unmixed sand or cement at the bottom. A spot board keeps the wet mix accessible while working, reducing trips to the mixer.

Take care when mixing anything with lime or cement, as these can pose health hazards.

What Makes The Best Mix For Rendering?

A commonly used mix is a 6:1:1 ratio of sand, cement, and lime for external rendering. Some prefer a 4:1:1 mortar mix, though it’s less common for exterior walls. Building sand isn’t suitable, though a small amount can be added to the base coat, but not the topcoat. Plastering sand and sharp sand are stronger choices. Lime adds elasticity, allowing for building movement, and makes the mix self-curing and breathable, preventing moisture build-up. Lime also creates a creamy mix for a smooth, flat finish and straight edges.

Sand & Cement Render Vs. Acrylic Render

The choice of render depends on factors like local climate, house age, building materials, and budget. Recent innovations have improved render quality, with options that are waterproof, breathable, self-cleaning, through-colored, algae/fungi resistant, and UV resistant. Each type has pros and cons, but all are excellent investments.

Acrylic render doesn’t always need painting as tinted mixes are available, unlike cement and sand render. However, it is generally more expensive and harder to apply, though often premade and ready to use. It dries in a few days, while traditional cement renders can take a month or more. Acrylic render lacks the breathability of traditional renders, though some modern versions address this with ongoing improvements.

Final Thoughts

Sand and cement render has been a trusted method for centuries, providing excellent protection and adding value and appeal to properties. Modern additives have extended the life of renders to 20, 30, or even 50 years. The variety of renders available today is broader than ever, with new types continually added. Traditional sand and cement (and lime) render remains in use, often as a base for modern 'thin coat' types like mineral and silicone renders.

For guidance and advice, consult Midrender. With many products available, choosing the right one can be overwhelming. Rendering a property is a cost-effective alternative to moving or expensive renovations, avoiding stress and upheaval. Rendering is relatively quick and painless, weather permitting, with stunning results. This technique, combined with cladding, creates a beautiful contemporary look, increasing property value, protecting against weather damage, and improving energy efficiency.

Expert Frequently Asked Questions

Sand and cement render is a mixture applied to exterior walls to protect them from weather damage and improve their appearance. It typically consists of sand, cement, and lime.

The traditional mix ratio is 6 parts sand : 1 part cement : 1 part lime.

Lime makes the mix more elastic, allowing for building movement and reducing the likelihood of cracking. It also improves breathability and workability.

No, building sand is generally unsuitable. It's best to use sharp sand or rendering/plastering sand for optimal results.

Traditional sand and cement render can take up to a month to dry fully. Modern alternatives like acrylic render may dry in just a few days.

Sand and cement render is more traditional, breathable, and usually requires painting. Acrylic render often comes pre-colored, dries faster, but is generally less breathable and more expensive.

Yes, render can improve your home's insulation, potentially reducing energy costs.

It's generally best to remove old render before applying new render to ensure proper adhesion and avoid future issues.

Author:

Richard Renderman, your trusted rendering expert at MidRender, is passionate about the art of rendering. With years of experience,he crafts…

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